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Part 3:
Decontamination procedures

Chapter 1
Introduction

Decontamination is the combination of physical and chemical processes that kills or removes pathogenic microorganisms. Decontamination of premises where infected animals have been housed and other possible fomites reduces the risk of the spread of infectious diseases to new animals. It is thus an important part of the control and eradication of major exotic or emergency livestock diseases.

The interpretation of exotic/emergency in relation to a disease depends upon the country involved. For this reason, detailed discussion in this section is confined to the OIE List A diseases, all but one of which have a viral aetiology. These diseases are considered serious even in countries where they are presently endemic; eradication is always recommended where possible. It is recognized that many List B and even unlisted diseases have serious implications in countries where they occur and that they would have even more serious implications should they be introduced into countries presently free of them. Nevertheless, for the sake of consistency, the emphasis in this manual is on the List A diseases. The exceptions are rabies and bovine spongiform encephalopathy (BSE), List B diseases with such serious implications for human health that they have been included.

Thorough decontamination, which involves close cooperation between farmers and all personnel involved in the cleaning and disinfection procedures, reduces the period between slaughter and restocking on contaminated and affected properties.

This manual provides guidelines for the decontamination of premises where animals infected with a specified disease agent have been held.

Identification of the disease agent is fundamental for designing an appropriate decontamination strategy. A sound understanding of the agent's biological properties and the mechanisms of disease spread can then form the basis for strategic planning. The basic microbiological principles of isolation of the source of infection and decontamination of personnel, equipment, vehicles and sites are of major importance. Personal decontamination procedures, when properly carried out, permit the safe movement of personnel from property to property in the extensive surveillance activities that form a large and vital part of any eradication campaign. Preliminary cleaning is invariably needed before any chemical disinfectants are used; this aspect cannot be overemphasized. Mechanical brushing of surfaces with a detergent solution is highly effective in removing contaminating viruses and is fundamental for achieving effective chemical decontamination. The procedures described may appear simple and tedious but persistence and attention to detail are vital for successful elimination of the disease agent.

This manual concentrates on a relatively narrow range of disinfectants and other chemicals in six general groups:

All the above disinfectants are effective against a broad range of viruses. Consequently, disinfectants are recommended that are generally available in large quantities.

It should be noted that common chemical names are used because they are easily understood by all personnel with basic scientific knowledge. Clear instructions are given for the dilution and application of these disinfectants in Table 4.

How to use the decontamination procedures part of the manual

The decontamination part has a series of simple tables that clearly and simply set out information on cleaning, disinfection and safety precautions regarding specified animal disease agents.

Chapter 2
Know the enemy - the emergency disease agent

In order to eliminate disease viruses/agents from clothing, vehicles, tools, carcasses or the environment, there must be a good understanding of the general properties of each infectious agent and the subtle ways each may persist in the environment and infect other animals. The following tables and graphs quickly show the individual characteristics of each disease.

The set of tables and figures presented in this section categorize the viruses and agents according to their physical characteristics to show clearly which disinfectant is best used for inactivation.

DISINFECTANT SUSCEPTIBILITIES OF IMPORTANT DISEASE AGENTS

The viruses/disease agents responsible for serious/emergency diseases can be categorized according to their size and whether or not they contain lipid. On this basis two categories of viruses can be identified as follows:

Table 1 shows the virus families, species affected, main mode of transmission and category of the OIE List A animal virus diseases, rabies and bovine spongiform encephalopathy.

TABLE 1.1
Disinfectant susceptibilities of viruses

Virus familyStructure1DiseasesSpecies affectedTransmissionCategory of virus2
Asfaviridaelarge-sized dsDNA envelopedAfrican swine feverswineingestion, contact ticks (Ornithodoros)A
Bunyaviridaemoderate-sized ssRNA envelopedRift Valley fever3 Nairobi sheep diseaseruminants
humans
dogs
sheep
goats
insect vectorsA
Caliciviridaesmall-sized ssRNA non-envelopedvesicular exanthemaswineingestionB
Orthomyxo-Viridaemedium-sized ssRNA envelopedavian influenzaavian speciesaerosols, ingestionA
Paramyxoviridaemedium sized ssRNA envelopedNewcastle diseaseavian speciesaerosols, ingestionA
rinderpestruminants swineaerosols, ingestion
peste des petits ruminantssmall ruminantsaerosols, ingestion
Picornaviridaesmall-sized ssRNA non-envelopedfoot-and-mouth disease3ruminants swineaerosols, ingestionB
swine vesicular diseaseswineaerosols, ingestion
Poxviridaelarge-sized dsDNA envelopedsheep/goat pox lumpy skin diseasesheep and goats cattlecontact, insect vectorsA
Reoviridaemedium-sized dsRNA non-envelopedAfrican horse sickness3 bluetongueequidae dogs ruminantsinsect vectorsB
Rhabdoviridaemedium-sized ssRNA envelopedrabies rabies-like virusesall mammalian speciesinfected animals (mainly bites)A
vesicular stomatitisruminants, horses, swine, humansinsect vectors

1 ds = double stranded; ss = single stranded.
2 Category A - best disinfectants are detergents, hypochlorites, alkalis, Virkon®, glutaraldehyde.
Category B - best disinfectants are hypochlorites, alkalis, Virkon®, glutaraldehyde; acids effective for foot-and-mouth disease virus.
Classical bactericides like quaternary ammonium compounds and phenolics are not effective against these viruses.
Category C - these viruses fall between Categories A and B in sensitivity to the best disinfectants such as hypochlorites, alkalis,Virkon®, glutaraldehyde.

3 Acidic disinfectants have traditionally been used for these pathogens.
Note: Details of concentrations and applications of specific disinfectants are found in Table 4.

TABLE 1.2
Diseases caused by other agents

AgentDiseaseSpecies affectedTransmission
Prion1bovine spongiform encephalopathy (BSE)cattle
antelope
humans
cats
ingestion of nervous tissue and possibly certain other tissues of infected animals; transmission in cattle possibly transplacental.
Mycoplasma mycoides mycoides SC1contagious bovine pleuropneumonia2cattlecontact, aerosol

1 Special inactivation is required.
2 Decontamination is not usually necessary during a stamping-out campaign for CBPP. However, if necessary, the organism is inactivated by 1 percent phenol solution in 3 minutes. 0.05 formaldehyde solution in 30 seconds or 0.01 percent mercuric chloride solution in 1 minute.

DISINFECTANT/ CHEMICAL SELECTIONS FOR PARTICULAR VIRUSES

Tables 2.1 to 2.15 show how to select a disinfectant or chemical to disinfect a range of commonly contaminated items for each disease or group of diseases. The list of disinfectant groups has been kept as short and simple as possible. Where a common decontamination/disinfection strategy is recommended, diseases are grouped. Each disinfectant table gives a list of items that could be contaminated during a disease outbreak and lists the best disinfectants or procedures to be used. The list aims to give the operator more than one choice of disinfectant.

There are five groups of disinfectants:

These are explained in more detail in Part 3, Chapter 3. The sixth group, insecticides, only applies to diseases that are insect-vector borne.

A key to the recommended disinfectants/chemicals is shown at the end of Table 2. Diseases with similar disinfection procedures are grouped together.

TABLE 2.1
Disinfectant/chemical selections and procedures — African horse sickness; category B virus

Item to be disinfectedDisinfectant/chemical/procedure
Live animalsEuthanize if moribund, vaccinate, insect control (stabling at night)
CarcassesBury or render, not for pet food.
Animal housing/equipmentN/A
EnvironsN/A
HumansN/A
Electrical equipmentN/A
WaterKeep horses away from vector insect habitat (stables on high ground, insect-proof stables, stable horses from dusk until dawn).
FeedBury only if contaminated with blood.
Effluent, manureN/A
Human housingN/A
Machinery, vehiclesN/A
ClothingN/A
AircraftN/A

N/A = not applicable

TABLE 2.2
Disinfectant/chemical selections and procedures — African swine fever and classical swine fever; category A viruses

Item to be disinfectedDisinfectant/chemical/procedure
Live animalsEuthanization (ASF) or vaccination (CSF)
CarcassesBury or burn
Animal housing/equipment1,2a, 2b or 2c, 3
EnvironsConsider 6a or 6b for tick eradication or burn wooden structures, otherwise N/A.
Humans1
Electrical equipment5c
Water 
tanksDrain
damsN/A
FeedBury or burn
Effluent, manureBury or burn, 4, 3
Human housing1, 2a, 2b, or 2c
Machinery1, 3
Vechicles1, 3
Clothing1, 2a, 2b or 2c, 3
Aircraft1, 2c

N/A = not applicable

TABLE 2.3
Disinfectant/chemical selections and procedures — avian influenza and Newcastle disease; category A viruses

Item to be disinfectedDisinfectant/chemical/procedure
Live birdsEuthanization or vaccination
CarcassesBury or burn
Animal housing/equipment1, 2a, 2b, 2c, 3
EnvironsN/A
Humans1
Electrical equipment5c
Water 
tanksDrain to pasture where possible.
damsDrain to pasture if practicable, otherwise N/A.
FeedBury
Effluent, manureBury or burn 4,3
Human housing1, 2a, 2b, 2c
Machinery, vehicles1, 3
Clothing1, 2a, 2b, 2c, 3
Aircraft1, 2c

N/A = not applicable

TABLE 2.4
Disinfectant/chemical selections and procedures — bluetongue; category B virus

Item to be disinfectedDisinfectant/chemical/procedure
Live animalsVaccination
CarcassesBury or burn normally, but this has no effect on virus spread.
Animal housing/equipmentN/A
EnvironsDecrease or keep sheep away from vector insect habitats (low-lying marshy areas).
Humans1
Electrical equipmentN/A
WaterN/A
FeedN/A
Effluent, manureN/A
Human housingN/A
MachineryN/A
Vehicles, aircraft6a or 6b for aircraft disinfection if necessary
ClothingN/A

N/A = not applicable

TABLE 2.5
Disinfectant/chemical selections and procedures — BSE; non-viral disease agent: prions; special inactivation necessary

Item to be disinfectedDisinfectant/chemical/procedure
Live animalsQuarantine, then euthanize according to disease strategy.
CarcassesBury with care or burn.
Animal housing/equipmentBury or burn all contaminating birth materials, manure or carcasses. 1 then 2a
HumansEnsure that contamination does not occur - protective clothing, masks;
respirators when removing the brain.
Electrical equipmentN/A
WaterN/A
FeedBury; burn only if contaminated with birth material, manure or carcasses.
Effluent, manureBury or burn
Human housingN/A
Machinery, vehiclesN/A
ClothingBurn if heavily contaminated.
AircraftN/A

N/A = not applicable

TABLE 2.6
Disinfectant/chemical selections and procedures — foot-and-mouth disease, swine vesicular disease and vesicular exanthema; category B viruses 1

Item to be disinfectedDisinfectant/chemical/procedure2
Live animalsEuthanization or vaccination
CarcassesBury or burn; 3, 4
Animal housing/equipment2, 3
Environs3
Humans1, 4b
Electrical equipment5c
Watertanks, dams3
FeedBury or 5b
Effluent, manureBury or 4
Human housing2, 4b
Machinery2c, 3, 4
Vehicles2c, 3, 4
Clothing2, 2c, 3, 4b
Aircraft2c

1 All of these vesicular diseases are category B viruses.
2 Acids are usually preferred for FMDV.

TABLE 2.7
Disinfectant/chemical selections and procedures — lumpy skin disease and sheep and goat pox; category A viruses

Item to be disinfectedDisinfectant/chemical/procedure
Live animalsEuthanization or vaccination (LSD)
CarcassesBury or burn
Animal housing/equipment1 (to clean) followed by one of 2, 3, 4b or 5
Environs2, 3 or 4b
Humans1, 2, 3b or 4b
Electrical equipment5c
Watertanks, damsDecrease vector insect habitat
FeedBury or burn
Effluent, manureBury; 6a or 6b for insect control
Human housing1 followed by 2, 3 or 4b
Machinery, vehicles1 followed by 2, 3 or 4b
ClothingDestroy if not valuable, or 2, 3 or 4b
Aircraft1 followed by 2 or mild 3, or 4b

TABLE 2.8
Disinfectant/chemical selections and procedures — peste des petits ruminants and rinderpest; category A viruses

Item to be disinfectedDisinfectant/chemical/procedure
Live animalsEuthanization or vaccination
CarcassesBury or burn
Animal housing/equipment1 (to clean) followed by 2a, 2b, 2c or 3 if necessary
Environs2 or 3
Humans1, 2c or 4b
Electrical equipment5c
Watertanks, damsDrain to pasture where possible
FeedBury contaminated feed
Effluent, manure2, 3, 4 then bury
Human housing1 (to clean) followed by 2a, 2b, 2c or 3 if necessary
Machinery, vehicles1 (to clean) followed by 2a, 2b, 2c or 3 if necessary
Clothing1 (to clean) followed by 2a, 2b, 2c or 3 if necessary
Aircraft1 (to clean) followed by 2a, 2b, 2c or 3 if necessary

TABLE 2.9
Disinfectant/chemical selections and procedures — rabies; category A virus

Item to be disinfectedDisinfectant/chemical/procedure
Live animalsDestroy without damaging head; beware of being bitten.
Dead animalsSubmit head to a rabies diagnostic laboratory in an appropriate infectious goods container for confirmation of infection; burn or bury the remainder of the carcass.
Animal housing/equipment1 (to clean) followed by 2
EnvironsN/A
HumansBites should be thoroughly washed with 1 then cleaned with a disinfectant suitable for human wounds. The offending animal should be euthanized and the head sent for confirmation of infection. Unless the animal can be shown conclusively to be free from infection, a post-exposure course of human diploid cell vaccine (HDCV) and human immunoglobulin (RIGH) should be started.
Electrical equipmentN/A
and machinery 
Watertanks, damsN/A
Feed,N/A
Effluent/manureBurn or bury
Human housing, clothingN/A
Vehicles, aircraftN/A

N/A = not applicable

TABLE 2.10
Disinfectant/chemical selections and procedures — Rift Valley fever; category A virus

Item to be disinfectedDisinfectant/chemical/procedure
Live animalsQuarantine, then decrease insect vectors; 6a or 6b
CarcassesBury or burn. Take extreme care and guard against blood splash, aerosols, fomites contacting humans.
Animal housing/equipment1 (to clean) followed by 2 or 4
Environs2 or 4 and insect control 6a or 6b
Humans2c or 4b
Electrical equipment5 if necessary
Watertanks, damsDecrease vector insect habitat.
FeedBury feed contaminated by blood, aerosols, fomites.
Effluent/manureDrain to pit/bury and 6a or 6b for insect control.
Human housing, clothing1 (to clean) followed by 2 or 4
Machinery, vehicles1 (to clean) followed by 2 or 4
Aircraft1 (to clean) followed by 2 or 4

TABLE 2.11
Disinfectant/chemical selections and procedures — vesicular stomatitis; category A virus

Item to be disinfectedDisinfectant/chemical/procedure
Live animalsTreat those in buffer zone with 6c (to prevent insects breeding in manure) and 6a or 6b (to prevent insects biting).
CarcassesBury or burn
Animal housing/equipment6a, 6b (to kill insects); 1 (to remove virus); 2, 3 also effective.
Environs6a
Humans, clothing1
Electrical equipment5c
Watertanks, damsDrain to pasture where possible; decrease vector insect habitat.
Feed6d
Effluent, manureBury or 6a
Human housing6a, 6b (to kill insects); 1 (to remove virus)
Machinery, vehicles, aircraft6b (to kill insects); 1 (to remove virus)

Key to Tables 2.1 – 2.11

1 Soaps and detergents 
2 Oxidizing agents: 
a: Sodium hypochlorite
 
b: Calcium hypochlorite
 
c: Virkon®
 
3 Alkalis:Do not use with aluminium and similar alloys.
a: Sodium hydroxide (caustic soda, NaOH)
 
b: Sodium carbonate anhydrous (Na2CO3)
washing soda (Na2CO3.10H2O)
 
4 Acids: 
a: Hydrochloric acid
 
b: Citric acid
 
5 Aldehydes: 
a: Glutaraldehyde
Glutaraldehyde is not too corrosive on metals but must not be used on humans or animals.
b: Formalin
 
c: Formaldehyde gas
Gaseous formaldehyde is dangerous and subject to error; it should only be used by experienced personnel and in controlled conditions.
6 Insecticides: 
a: Organophosphates
 
b: Synthetic pyrethroids
 
c: Ivermectin
 
d: Phostoxin
 

EPIDEMIOLOGICAL CONSIDERATIONS AFFECTING DECONTAMINATION PROCEDURES FOR PARTICULAR VIRUSES

Tables 3.1–3.16 summarize epidemiological factors that govern the extent of procedures to be employed in removing the disease agent. The recommended disinfectants and chemicals applicable to elimination of each disease agent are listed in Tables 2.1–2.14 and appropriate procedures are in Chapters 3, 4 and 5.

TABLE 3.1
Epidemiological consideration - African horse sickness

Disease featuresEpidemiologyComments
Aetiology/general propertiesA peracute, acute, subacute or mild insect-borne viral disease affecting mainly Equidae. Horses are most susceptible, mules less so and in donkeys disease is usually subclinical. Dogs also susceptible. Reoviridae (category B virus) with 9 known serotypes. Optimal pH for survival of the virus is 7.0-8.5. Resistant to detergents. Acid disinfectants most suitable for decontamination.Disinfectants applicable to category B viruses (Chapter 3).

Table 2.1
Incubation periodUsually 5–7 days; may be as short as 2 days. Incubation periods up to 21 days have been recorded, but longer than 10 days is rare.Decontamination procedures are determined by an incubation period of 40 days (OIE Code).
TransmissionTransmitted between susceptible animals by biting midges. Dogs can become infected by eating infected fresh uncooked horse meat. 
Airborne spreadThere is no aerosol spread of AHS. There may be wind-borne spread of infected vectors. 
Persistence in the environmentVirus is stable outside the host. Not destroyed by putrefaction and may retain infectivity in putrid blood for more than 2 years.Chapter 4
WildlifeZebras are highly resistant to the pathogenic effects of the disease.1 
Arthropod vectorsBiting midges of the family Culicoides are the most important vectors. Experimentally, three species of mosquitoes, the brown dog tick and the camel tick have transmitted the virus.Chapter 3
ZoonosisHumans are not affected. 

1 Here and subsequently, there is no reason why feral domestic species should differ greatly in susceptibility from their captive cohorts and “wildlife” has a totally different implication.

TABLE 3.2
Epidemiological considerations - African swine fever

Disease featuresEpidemiologyComments
Aetiology/general propertiesA highly contagious, peracute, acute or (rarely) subacute viral disease of pigs. Asfaviridae (category A virus); stable over wide pH range from pH 4–10.Disinfectants applicable to category A viruses (Chapter 3).
Detergents, oxidizing agents and alkalis are the disinfectants of choice.
Incubation period5–15 daysDecontamination procedures are determined by an incubation period of 40 days (OIE Code).
TransmissionASF virus is excreted by infected domestic pigs in faeces, urine and all secretions in high concentration. Virus is transmitted readily by direct contact or ingestion of infected pig meat, e.g. by swill feeding or scavenging. Recovered animals will retain virus for 2–6 months. Transfer by fomites, e.g. infected vehicles, contaminated clothing, needles. 
Airborne spreadNot a factor; can occur over very short distances, e.g. in the same pig pen. 
Persistence in the environmentPigs that recover from ASF may remain carriers and may shed virus for up to 2 months. Virus survives for long periods in a protein environment: in serum at room temperature for 18 months, in refrigerated blood for at least 6 years, at 37°C for a month and at 55°C for 30 minutes; in raw and processed meat for several weeks to months, especially if frozen. Resistant to putrefaction, with persistence in faeces at room temperature for 11 days and decomposed serum for 15 weeks. Pig pens in the tropics without disinfection were not safe after 3 days; safe after 5 days.Chapter 4
WildlifeAll African wild porcines - warthogs, bush pigs and giant forest hogs - are susceptible to infection but completely resistant to the pathogenic effects of the virus. They act as reservoir hosts in the sylvatic cycle. European wild boar are fully susceptible and mortality rates are similar to those of domestic pigs. 
Arthropod vectorsSylvatic life cycle between warthogs and Ornithodoros moubata complex ticks, which can transmit virus to domestic pigs. A cycle between Ornithodoros and domestic pigs occurs in some areas. Mechanical transmission can occur by stable flies for 24–48 hours after ingestion of infected blood; other blood-sucking pig parasites may be implicated in the spread of ASF within pig herds but this is unproven.Where applicable, identify tick species and spray defined area with insecticide.
ZoonosisHumans are not affected. 

TABLE 3.3
Epidemiological considerations - avian influenza (fowl plague)

Disease featuresEpidemiologyComments
Aetiology/general propertiesA highly contagious generalized viral disease of poultry and other birds.
Orthomyxoviridae (category A virus) with strains of varying virulence.
Virus is relatively stable but is rapidly inactivated at extremes of pH.
Disinfectants applicable to category A viruses (Chapter 3).

Table 2.4
Incubation periodIncubation period is variable from a few hours to 3 days.Decontamination procedures are determined by an incubation period of 21 days (OIE Code).
TransmissionVirus is shed from the respiratory tract and in faeces for 30 days post infection in recovered birds.
The disease spreads rapidly within the flock by direct contact. Indirect spread occurs via contaminated people, articles, feed and vehicles.
 
Airborne spreadRapid within the flock but not important between flocks.Chapter 3
Persistence in the environmentRemains viable in water and faeces for 32 days and under a wide variety of environmental conditions at pH 7-8.Chapter 4
Persistence in productsAl virus survives only a few days in carcasses at ambient temperatures and up to 23 days when refrigerated. Packaging and drips from infected carcasses can be contaminated with virus.
Eggs laid in the early phase of disease could have Al virus in albumen, yolk and on the surface.
Al virus can penetrate intact eggshell and has been isolated from fertile eggs.
Poultry offal meals should be rendered but recontamination could be a problem.
 
Arthropod vectorsN/A 
Wild birdsWater fowl and many species of wild birds are reservoirs for the virus, without showing significant disease; the opportunity exists for mutation of virus to virulent pathogenic strains. 
ZoonosisHumans were until recently not thought to be affected but recently cases in humans, some fatal, have been diagnosed. 

N/A = not applicable

TABLE 3.4
Epidemiological considerations - bluetongue

Disease featuresEpidemiologyComments
Aetiology/general propertiesArthropod-borne viral disease of mainly sheep, goats and deer.
Reoviridae (category C virus); 24 serotypes comprising countless strains of varying virulence.
Infection of cattle, although usually subclinical, is of great epidemiological significance.
Unstable below pH 6.5 and at high temperatures, readily inactivated by acid and alkaline disinfectants.
There are no requirements for any procedures to be employed.
Incubation periodAbout 7 days with natural infection; 2–15 days but usually 4–6 days with experimental infection. 
TransmissionNot contagious; transmission mainly by arthropod vector but may be transmitted in semen or transplacentally by viraemic animals. 
Arthropod vectorsThe disease is transmitted by biting midges, (Culicoides spp.) Cattle are the main amplifying hosts.Disinfection would be impractical in most circumstances. Table 2.5
Airborne spreadAerosol spread is not a factor but wind-borne spread by aerial drift of infected Culicoides spp. may occur. 
WildlifeAfrican antelopes do not develop clinical disease and may act as amplifying hosts. Severe disease is reported in desert bighorn sheep. 
ZoonosisHumans are not affected. 

TABLE 3.5
Epidemiological considerations - bovine spongiform encephalopathy

Disease featuresEpidemiologyComments
Aetiology/general propertiesA transmissible spongiform encephalopathy of cattle caused by an unconventional agent.
Prion (special inactivation required).
Disinfectants are not effective.
Reported in domestic cats; other species can be infected experimentally.
Table 2.6
Incubation periodProlonged - 2 years or more in cattle; most cases occur in cattle aged between 3 and 7 years.OIE Code does not specify a maximum incubation period.
TransmissionIngestion of contaminated carcass meal that contains nervous tissue from affected animals or possibly from sheep with scrapie. 
Airborne spreadN/A 
Persistence in the environmentCan persist for very long periods in the environment; presumed to act in similar way to scrapie agent. 
WildlifeSpongiform encephalopathies have been reported in antelopes in British zoos and in large and small cats. 
Arthropod vectorsN/A 
ZoonosisThere is convincing evidence that the BSE agent causes a fatal transmissible encephalopathy, new variant Creuzfeld-Jakob disease, in humans. 

N/A = not applicable

TABLE 3.6
Epidemiological considerations - classical swine fever (hog cholera)

Disease featuresEpidemiologyComments
Aetiology/general propertiesContagious acute, subacute, chronic or inapparent viral disease of pigs.
Togaviridae (category A virus); strains of varying virulence. Virus is stable at pH 4-10 but rapidly inactivated below pH 3; relatively heat stable but sensitive to desiccation, ultraviolet light and putrefaction.
Disinfectants applicable to category A viruses
(Chapter 3).
Table 2.2
Incubation periodIncubation period for acute disease is usually 2–6 days.Decontamination procedures are determined by an incubation period of 40 days (OIE Code) and by epidemiology.
TransmissionDisseminated mainly by direct contact with infected pigs. Infected pigs excrete virus in faeces, urine, nasal and lachrymal secretions. Virus is shed before clinical signs are seen.
The disease can spread rapidly within pig populations. Carrier sows can infect piglets transplacentally and large amounts of virus are shed at farrowing.
Spread by movement of infected pigs via sales, fomites and contaminated vehicles, feeding of swill and multiple use of hypodermic needles and vaccine.
Discard needles and partially used bottles.
Airborne spreadN/A 
Persistence in the environmentSensitive to ultraviolet radiation; will survive in contaminated pig pens for only a few days.Chapter 4
Persistence in productsPigmeat products can maintain the virus for up to 2–4 months in salted or brined meat.
Pork products, fresh and frozen, can maintain infective CSF virus for months if kept cool and years if frozen; 2–4 months in salted or brined pork.
 
Wild animalsEuropean wild boar are an important reservoir host of the virus. 
VectorsGenerally unimportant. Mosquitoes and two species of stable fly have been shown to be capable of mechanical transmission of CSF virus. 
ZoonosisN/A 

N/A = not applicable

TABLE 3.7
Epidemiological considerations - contagious bovine pleuropneumonia (CBPP)

Disease featuresEpidemiologyComments
Aetiology/general propertiesAcute, subacute or chronic disease of cattle and water buffaloes.
Mycoplasma mycoides subsp. Mycoides SC (bovine biotype).
Mycoplasma has a low resistance to environmental factors and survives outside the host for less than 3 days in tropical conditions and less than 2 weeks in temperate conditions.
Decontamination procedures are generally not necessary in stamping-out campaigns for CBPP.
Incubation periodGenerally 3–6 weeks but may be as long as four months. 
TransmissionDisseminated by direct contact with infected cattle or water buffaloes. Infection is contracted by inhalation of infected droplets.
Chronic carrier animals are very important for persistence of the disease in an area and for its spread to new areas.
 
Airborne spreadVery important over short distances. 
Persistence in the environmentMycoplasma has a low resistance to environmental factors and survives outside the host for less than 3 days in tropical conditions and less than 2 weeks in temperate conditions. 
Persistence in productsN/A 
Wild animalsYaks and bison are susceptible. Antibodies have been found in some other species, e.g. camels and water buffaloes, but their significance is doubtful. 
VectorsN/A 
ZoonosisN/A 

N/A = not applicable

TABLE 3.8
Epidemiological considerations — foot-and-mouth disease

Disease strategiesEpidemiologyComments
Aetiology/general propertiesHighly contagious viral, vesicular disease of cloven-footed animals.
Picornaviridae (category B virus); 7 serotypes with 60+ subtypes.
The virus is varyingly stable at pH 6.7-9.5; rapidly inactivated below pH 5 and above pH 11.
The virus is stable at low temperatures and when the relative humidity is above 60%.
The virus is moderately susceptible to ultraviolet light and rapidly inactivated at temperatures above 50°C.
Disinfectants applicable to category B viruses (Chapter 3).
Acid, alkali and chlorine-based disinfectants can be used, provided care is taken that they are not mixed together. Table 2.8
Incubation periodUsually 3–5 days
FMD virus is excreted 1–5 days prior to clinical signs, depending on incubation period.
Decontamination procedures are determined by an incubation period of 14 days (OIE Code).
TransmissionVirus is excreted from nasal passage, saliva, milk, semen, faeces, urine and in vast amounts from ruptured vesicles. Pigs excrete up to 3 000 times more virus than other animals.
The disease is rapidly spread by direct contact, especially at shows and sales.
Indirect contact with contaminated people, fomites, milk, manure vehicles and illegal swill feeding is well documented.
Cattle remain carriers for at least 27 months, sheep for 9 months; pigs are not longterm carriers.
All procedures listed in this manual should be observed. Personal decontamination is important (Section 4).1
Preliminary pre-slaughter spraying should be carried out, especially in piggeries and enclosed animal houses.
Persistence in the environmentFMD virus may remain infective in the environment for several weeks, possibly longer in the presence of soil, manure, dried animal secretions, straw, hair and leather.Chapter 4
Persistence in productsFMD virus is inactivated in “setting” meat (not pigmeat) but is not inactivated in offal, bone marrow, lymph nodes or blood clots.
FMD virus survives in salted/cured meats, hides, milk, dairy products, wool and semen.
These facts determine the extent of operations following tracing of stock during a disease outbreak.
Airbone spreadCan be extremely widespread over long distances if conditions of temperature, wind speed, humidity, terrain, atmosphere and viral concentration are right.
Cattle are usually the indicator, since they ventilate 10 times more air than other species.
Preliminary spray of buildings
WildlifeFeral and wild animals have potential to be an important risk in perpetuating or disseminating FMD virus. 
Arthropod vectorsNot applicable. Mechanical transfer could occur. 
ZoonosisVery rarely zoonotic. It is known to cause vesicles on hands and lips.

Human nasal passages can mechanically harbour the virus for 24–27 hours, despite masks and noseblowing.
If a person is affected, they must not have contact with susceptible animals until cleared of infection.
Recommend no contact with susceptible stock for 72 hours.

1 Where light contamination has occured, especially in dry, hot areas, the intensity of decontamination necessary can be assessed by the LDCC.

TABLE 3.9
Epidemiological considerations - lumpy skin disease

Disease featuresEpidemiologyComments
Aetiology/general propertiesAn acute highly infectious skin disease of cattle. Poxviridae (category A virus); inactivated after heating for 1 hour at 55°C. Susceptible to a wide range of disinfectants.Disinfectants applicable to category A virus (Chapter 3). Table 2.9
Incubation periodIn naturally infected animals, incubation period is 2–4 weeks; in experimental infections, 5 days.Decontamination procedures are determined by an incubation period of 21 days (OIE Code).
TransmissionMostly the result of insect transmission, with many types of biting insects implicated. The virus could be transmitted in milk, semen, blood and lesions in cattle hides. 
Airborne spreadWind-borne spread of the insect vector only. 
Persistence in the environmentThe virus is very resistant and can remain viable for long periods on or off the animal host. It survives well in cold temperatures but is susceptible to sunlight. 
WildlifeVermin, predators and wild birds might act as mechanical carriers of the virus. 
Arthropod vectorsStable and blow files are important in spread. Biting insects such as mosquitoes, midges and tsetse fly may play some role in the spread. 
ZoonosisHumans are generally regarded as being non-susceptible. 

TABLE 3.10
Epidemiological considerations - Newcastle disease (fowl pest)

Disease featuresEpidemiologyComments
Aetiology/general propertiesHighly contagious, generalized, viral disease of domestic poultry, caged birds and wild birds.
Paramyxoviridae (category A virus) strains vary in virulence: velogenic (high), mesogenic (moderate), lentogenic (low).
See disinfectants applicable to category A viruses (Chapter 3).
Incubation period2–6 days but can be as long as 15 daysDecontamination procedures are determined by an incubation period of 21 days (OIE Code).
TransmissionDepending on viral strain, birds can die without showing symptoms.
Virus is shed via respiratory tract and in faeces and is rapidly spread in the flock.
Disease is disseminated by direct contact and “carrier” state birds up to 120 days after infection;
indirectly by contaminated people, articles, formites, manure, feed and vehicles.
Preliminary aerial spray of buildings.
Airborne spreadGiven the right environmental conditions, ND virus has been known to disseminate over a wide area.Close down fans and ventilators. Preliminary aerial spray of building interior.
Persistence in the environmentVirus is inactivated by heat and direct sunlight (30 minutes) but can remain 21 days in cool weather in poultry litter and sheds. 
Persistence in productsViable virus remains in the carcass until decomposition is well advanced.
Isolated from bone marrow after several days at 30°C. Virus will remain viable in carcass meat for more than 250 days at 14°C.
Eggs laid in the early phase could contain ND virus on the surface; egg pulp likely to be infected.
Procedures for decontamination of buildings, hatcheries, slaughterhouses as above.
Wild birdsCould be reservoir, become infected in an outbreak or transmit mechanically - “carrier” state can exist up to one year. 
Arthropod vectors“Flies” are thought to transmit ND virus mechanically. 
ZoonosisHeadache and flu-like symptoms can occur in humans. Conjunctivitis usually mild but can occasionally become severe and cause impairment of vision. It is suspected that person-to-person transmission may occur.Infected people to have no contact with susceptible stock until cleared of virus.

TABLE 3.11
Epidemiological considerations - rabies

Disease featuresEpidemiologyComments
Aetiology general propertiesAn almost invariably fatal viral encephalitis affecting all warm-blooded mammals. Rhabdoviridae (category A virus).Disinfectants applicable to category A viruses (Chapter 3).
Incubation periodIncubation period varies considerably, from 4 days to 6 months or more depending on a number of factors. Virus can be excreted in saliva up to 7 days prior to symptoms appearing.Incubation period is not a determinant of decontamination procedures; more from initial clinical signs. (OIE Code maximum incubation period is 6 months.)
TransmissionRabies virus is transmitted directly by the bite of a rabid animal or contamination of a fresh wound with infected saliva or contamination of mucous membranes. Virus cannot invade intact skin. Exceptionally, respiratory and oral transmission can occur.When a known rabid animal has dripped saliva, the immediate environment can be disinfected for cosmetic reasons or to allay public concern.
Airborne spreadNot applicable, except in an extreme situation (as above). 
Persistence in the environmentRabies virus is fragile outside the host and is not viable for long. Environmental contamination is of very little significance, other than aerosol contamination in bat caves. Rabies virus is inactivated by exposure to sunlight and temperature above 56°C.Personnel must be made aware of the danger of viral contamination if handling rabid animals and they must be fully aware of personal decontamination procedures.
Persistence in productsMilk from rabid cows contains virus but obviously will not be used for human consumption. If milk from incubating cows is processed, pasteurization will kill the virus. 
VectorsN/A 
WildlifeCould definitely be a problem with all warm-blooded animals. 
ZoonosisMost important; can arouse hysteria in human population.Initial first aid is to scrub wound with hot water and soap.

N/A = not applicable

TABLE 3.12
Epidemiological considerations - Rift Valley fever

Disease featuresEpidemiologyComments
Aetiology/general propertiesAn acute insect-borne viral disease affecting mainly ruminants and humans.
Bunyaviridae (category A virus)
Virus very susceptible to acid pH and readily inactivated below pH 6.2; most stable within pH 7-8.
Disinfectants applicable to category A viruses
(Chapter 3).
Table 2.12
Incubation periodUsually 2–6 daysDecontamination procedures are determined by an incubation period of 30 days (OIE Code).
TransmissionPredominantly a vector-borne disease. Aerosol transmission and contact with infected carcasses are important means of spread to humans. 
Airborne spreadWind-borne dispersal of infected vectors is a means of spread of RVF.Chapter 3
Persistence in the environmentThe virus is destroyed by strong sunlight/ultraviolet radiation.
Stable in aerosol form at 24°C and relative humidities of 50–85%.
Can survive in dried blood for up to 3 months.
 
WildlifeSpecies most likely to harbour the virus are goats, camels and buffalo. 
Arthropod vectorsMajor vectors are certain species of mosquitoes. Ticks and biting midges have been implicated. 
ZoonosisHumans can be affected.Chapter 4

TABLE 3.13
Epidemiological considerations - rinderpest/peste des petits ruminants (PPR)

Disease featuresEpidemiologyComments
Aetiology/general propertiesContagious generalized viral disease mainly of cattle; usually fatal.
PPR mirrors rinderpest in all respects but is specific to sheep and goats; Asian pigs are more susceptible to rinderpest than European pigs.
Paramyxoviridae (category A virus)
PPR virus is stable between pH 7.2-7.9 but is rapidly inactivated at pH values less than 5.6 or greater than 9.6.
Disinfectants applicable to category A viruses
(Chapter 3).
Table 2.10
Incubation period2–6 days but may be as long as 15 days.
Virus appears in blood excretions and secretions 1–2 days before clinical signs.
Decontamination procedures are determined by an incubation period of 21 days (OIE Code).
TransmissionTransmission is via the respiratory tract and close contact. Virus present in saliva, faeces, urine, milk and products of abortion.
In the few animals that do recover, there is no “carrier” state but milk may be infectious 45 days after clinical recovery.
Disease transmitted by movement of cattle; indirectly by contaminated clothing articles and vehicles, though unlikely because of low persistence of virus in environment.
Preliminary disinfection and clean up only suggested.
Airborne spreadPossible over several hundred metres, mainly at night. High and low humidity aid survival but virus is rapidly destroyed at relative humidity 50–60%.No action if control measures are in place.
Persistence in the environmentRinderpest/PPR virus is not very stable and does not survive more than two or three days.
Because of viral emission, saleyards and abattoirs could be contaminated.
Contaminated pastures would be non-infective after 6–24 hours, depending on sun/shade.
 
Persistence in productsRinderpest/PPR virus is rapidly inactivated by putrefaction. “Setting” meat would be expected to inactivate the virus. 
Wild animalsBuffalo, feral cattle and probably deer, depending on stock density and degree of contact. Feral pigs should not be a problem but Asian pigs and warthog can be affected. 
Arthropod vectorsNot considered applicable. 
ZoonosisHumans are not affected. 

TABLE 3.14
Epidemiological considerations - sheep and goat pox

Disease featuresEpidemiologyComments
Aetiology/general propertiesA highly contagious viral disease of small ruminants. Poxviridae (category A virus)
Susceptible to a wide range of disinfectants, including detergents.
Inactivated after heating for 1 hour at 55°C.
Disinfectants applicable to category A viruses
(Chapter 3).
Table 2.9
Incubation periodUsually 12 days but varies from 2 to 14 days.Decontamination procedures are determined by an incubation period of 21 days (OIE Code).
TransmissionMost transmission is by direct contact via the respiratory system. Contact and mechanical transmission by insects can occur. 
Airborne spreadShort-distance aerosol transmission from nasal secretions and saliva is an important method of spread. 
Persistence in the environmentThe virus is very resistant and can remain viable for long periods on or off the animal host.
Virus is susceptible to sunlight but survives well in cold temperatures.
May persist for up to 6 months in a suitable environment.
 
WildlifeFeral goats would pose a risk; vermin, predators and wild birds might act as mechanical carriers. 
Arthropod vectorsInsects can act as mechanical vectors over short distances. 
ZoonosisHumans are generally regarded as not being susceptible. 

TABLE 3.15
Epidemiological considerations - swine vesicular disease

Disease featuresEpidemiologyComments
Aetiology/general propertiesContagious viral disease of pigs; clinically indistinguishable from FMD.
Picornaviridae but an enterovirus (category B virus). The virus is very resistant to inactivation and is stable over a pH range of 2-12.
Relatively resistant to heating and drying.
Disinfectants applicable to category B viruses
(Chapter 3).
Table 2.8
Incubation period2–7 daysDecontamination procedures are determined by incubation period of 28 days
(OIE Code).
TransmissionVirus is excreted from ruptured vesicles for up to 10 days and in faeces for more than 3 weeks but a prolonged “carrier” state does not occur.
Spread by direct contact between animals; indirect spread by contaminated vehicles, fomites, people and illegal swill feeding.
Recrudescence of disease is well known.
All procedures in the decontamination manual pertaining to contaminated persons, buildings, vehicles and articles must be rigorously pursued.
Persistence in the environmentCan survive in pig faeces at least 5 months. 
Persistence in productsSurvives in salami and frozen carcasses for more than one year and in intestinal casings for at least 780 days. The virus is not destroyed by “setting” meat. 
Airborne spreadNot a factor. Aerial drift can occur over short distances from mechanical effluent spreading. 
WildlifeFeral pigs could be a problem, especially if allowed access to piggeries, dumps of discarded food waste or effluent runoff. Progress of the disease in feral pigs is unknown but probably would be erratic. 
Arthropod vectorsNot applicable. Mechanical transfer by flies and cockroaches is minimal. 
ZoonosisNot a factor but slight zoonotic capability is suspected.No action unless a suspect case is reported. Most likely to occur in staff highly exposed to lesions in an infected premises.

TABLE 3.16
Epidemiological considerations - vesicular exanthema

Disease featuresEpidemiologyComments
Aetiology/general propertiesAcute, contagious viral disease of pigs and marine mammals.
Calicivirus (category B virus); several different serotypes varying in virulence.
Virus mutates readily.
Marine mammals are probably a natural reservoir. Virus is reasonably resistant to inactivation. It is inactivated at or below pH 3 and above pH 9.
Disinfectants applicable to category B viruses (Chapter 3).

Table 2.8
Incubation periodIn natural outbreaks, 1–3 days (12 hr-12 days). Virus is shed 12 hours before vesicles appear.Decontamination procedures are determined by an incubation period of 28 days (OIE Code), as no OIE code exists for VE.
TransmissionVirus is shed in large quantities from ruptured vesicles. Faeces and urine do not appear to be infected.
Illegal feeding of swill is a primary cause of spread. Feeding contaminated fishmeal would be important. Spread by direct contact and movement of infected pigs. Mechanical spread by way of infected articles is inconsistent, but cannot be ignored.
 
Persistence in the environmentViral persistence in environment is uncertain but contaminated premises would be at risk for 3–4 months. 
Persistence in productsContaminated pigmeat remains infectious for 4 weeks at 7°C and for years when deep frozen. Cooking at 84°C under pressure does not destroy infectivity. 
Airborne spreadNot a factor 
WildlifeFeral pigs could be a problem in an outbreak. Feral pigs scavenging the shoreline could possibly pick up infection but the world distribution is centred on the west coast of America. 
Arthropod vectorsN/A. Blood-sucking pig parasites may spread disease in acute phase within the pig herd. 
ZoonosisHumans are not affected. 

N/A = not applicable

TABLE 3.17
Epidemiological considerations - vesicular stomatitis

Disease featuresEpidemiologyComments
Aetiology/general propertiesA contagious viral disease of cattle, pigs, horses and possibly sheep and goats.
Rhabdoviridae (category A virus); two distinct serotypes: Indiana and New Jersey.
Disinfectants applicable to category A viruses
(Chapter 3).
Incubation periodIn natural outbreaks 1–3 days but can vary up to 10 daysDecontamination procedures are determined by an incubation period of 21 days (OIE Code).
TransmissionVirus is shed in vesicular fluid and saliva for a few days only and has not been isolated from faeces and urine nor from saliva after lesions have healed.
Spread by direct contact.
The carrier animal state has not been demonstrated. Much of the epidemiology is unresolved.
Domestic animals are probably not the primary host. The virus enters only through damaged skin and mucous membranes. Transmission is enhanced by poor-quality food, which may damage mucous membranes. Spread indirectly by fomites and people.
Decontamination procedures would be limited to a preliminary disinfection and clean up.
Persistence in the environmentThe virus is not very stable and survives no more than several days in premises. 
Persistence in productsVirus is not found in edible animal tissue and would be destroyed by pasteurization. 
Airborne spreadN/A 
Wild animalsIn endemic areas, many wild life species are susceptible, e.g. deer, rodents, bats, feral pigs and, experimentally, rabbits, ferrets and cats; dogs appear resistant. Wild animals may act as reservoirs. 
Arthropod vectorsVS virus has been isolated from sandflies, mosquitoes, gnats and flies. They are probably involved in transmission both by bite and mechanically (Indiana strain).Disinfection would more than likely be impractical.
ZoonosisYes; human infection is via the respiratory tract and conjunctiva and through skin abrasions. Disease symptoms similar to influenza.Infected humans should have no contact with susceptible stock.

N/A = not applicable

COMPARISON OF AMPLIFICATION, PERSISTENCE AND RESISTANCE OF IMPORTANT INFECTIOUS ANIMAL DISEASE AGENTS

Figure 1 compares important animal disease agents using three parameters relating to decontamination principles:

In the figure each of three parameters is given a qualitative grade from 0–10. The higher the grading the more difficult it is to eliminate the disease agent from the environment.

FIGURE 21

Comparative histograms for important infectious animal disease agents, showing (A) amplification, (B) persistence, and (C) resistance

FIGURE 21

Keys:

AHSAfrican horse sickness
AIavian influenza
ASFAfrican swine fever
AUJAujeszky's Disease
BSEbovine spongiform encephalopathy
BTbluetongue
CSFclassical swine fever
EIequine influenza
FMDfoot-and-mouth disease
LSDlumpy skin disease
NDNewcastle disease
PPRpeste des petits ruminants
RABrabies
RINrinderpest
RVFRift Valley fever
SCRscrapie
SGPsheep/goat pox
SVDswine vesicular disease
SWFscrew-worm fly
TGEtransmissible gastroen-teritis
VEvesicular exanthema
VSvesicular stomatitis

Chapter 3
Weapons: disinfectants and chemicals for inactivation of exotic viruses and disease agents

INTRODUCTION

This section provides advice for the decontamination of premises where animals infected with a serious epidemic disease have been held. Most such diseases are caused by viruses; these recommendations are made on that basis.

Decontamination

Decontamination is the combination of physical and chemical processes to kill or remove pathogenic microorganisms; it does not necessarily result in sterility. A disinfectant is a chemical or mixture of chemicals capable of killing pathogenic microorganisms associated with inanimate objects.

Basic assessments

The most important initial information is the presumptive identification of the disease agent involved. Once established, the basic properties of the agent, most likely a virus, must be considered. What are the epidemiological characteristics of the spread of the virus? Has transmission occured by aerosol spread, oral ingestion, close contact or insect vectors? From the information gathered, a plan can be devised to establish priorities for decontamination (Prince, et al., 1991). Such a plan usually includes:

Depending on the disease agent involved, different decontamination procedures and disinfectants are likely to be used for different sites on a property (Kostenbauder, 1991).

In cases where the disease agent does not spread directly from animal to animal, e.g. bluetongue, a comprehensive decontamination of a property is not warranted. In contrast, some viruses, such as swine vesicular disease and foot-and-mouth disease, are relatively stable on inanimate objects and can be spread to remote animals on contaminated people, clothes and equipment. Viruses that can be spread by such contact will require the most comprehensive decontamination programmes.

Preliminary cleaning work is invariably needed before any chemical disinfectants are used. The natural processes of time, dehydration, warm temperature and sunlight will greatly assist the decontamination operation and should be considered in planning. A hot, dry, sunny day will cause rapid natural inactivation of an agent like Newcastle disease virus, whereas cold, damp, overcast conditions will assist its persistence.

Simple cleaning of surfaces by brushing with a detergent solution is effective in removing contaminating viruses and is fundamental for achieving effective chemical decontamination. Most disinfectants have reduced effectiveness in the presence of fat, grease and organic dirt. Every effort should be made to remove such coverings from all surfaces to be decontaminated. Hot water and steam are effective in cleaning many cracks and crevices where pathogens are likely to linger. The insides of pipework can often only be cleaned effectively by steam. If applied long enough for surfaces to approach 100°C, the interior of pipework will be effectively decontaminated.

Choice of disinfectant depends on the method of application and how an adequate wet contact time is to be maintained.

A knowledge of the properties of the contaminating virus is crucial in planning a decontamination strategy. Choosing the most appropriate disinfectant is dependent on the nature of the virus particles. Useful clues for predicting susceptibility are the presence or absence of lipid in the virus particles and the virus size (Klein and DeForest, 1981). In this predictive system, viruses fall into three groups, as given below.

Category A. Category A viruses are of intermediate to large size and contain lipid, which makes them susceptible to detergents, soaps and all the disinfectants listed in Chapter 3. Such viruses are susceptible to dehydration and often do not persist long except in cool, moist environments.

Category B. Category B viruses, e.g. picornaviruses and parvoviruses, have no lipid and are smaller and more hydrophilic. Such viruses are relatively resistant to lipophilic disinfectants such as detergents. Although they are sensitive to all the other disinfectants listed in Chapter 3, they are less susceptible than viruses in Category A. Classical bactericides such as quaternary ammonium compounds and phenolics are not effective against these viruses.

Category C. Category C viruses, e.g. adenoviruses and reoviruses, are intermediate in size and lack lipid. These viruses fall between Categories A and B in sensitivity to the best antiviral disinfectants such as hypochlorites, alkalis and oxidizing agents, e.g. Virkon® and aldehydes.

Table 1.1 groups viruses of veterinary significance in their families and also in terms of their susceptibilities to common disinfectants.

Precautions when using disinfectants

Chemicals usually kill microorganisms by toxic reactions; effective disinfectants are often toxic for animal and human tissues as well. Virtually all disinfectants have to be used with care to avoid occupational injuries or health problems. Table 5 provides some basic information about precautions and contra-indications when using the recommended disinfectants.

SELECTION OF DISINFECTANTS

This manual concentrates on a relatively narrow range of disinfectants that are effective against broad groups of viruses. Consequently, disinfectants are recommended that are generally available in large quantity. It should be remembered that in any large-scale decontamination of a farm or other infected premises, the cost of disinfectants will be relatively minor. Because labour and other operational costs will be high, it would be a false economy to use disinfectants at less than recommended concentrations. In any case, when disinfectants are diluted they invariably lose their effectiveness.

Flame guns may be useful supplements for drying decontaminated surfaces but they are dangerous and the risk of fire and injury must always be considered. Flame guns are not recommended as a primary means of decontamination.

In general, chemical names of disinfecting substances are used, because they are easily understood by all personnel with basic technical knowledge. This document generally avoids the use of brand or trade names, because such products are subject to change or restriction in their distribution. Appendix 2 shows the names of trade products and the distributors from which supplies can be obtained.

To simplify determinations, disinfectants are grouped into five chemical categories:

Each of these classes of disinfectants is discussed briefly here and shown in Table 4.

Commonly used general disinfectants, such as phenolics and quaternary ammonium compounds, are very effective antibacterials but have limited effectiveness against category B and C viruses; they are therefore not included in Table 4.

Products effective for decontamination of viruses on the hands and the skin are limited. Virkon® is reported to have low toxicity and to be effective against members of all 17 virus families but it has not been approved for use on skin. Alternatively, citric acid or sodium carbonate may be added to washing water to induce antiviral conditions by lowering or raising the pH as appropriate for the agent to be inactivated.

Soaps and detergents

Soaps and detergents are essential components of cleaning procedures prior to many of the decontamination procedures described here. In most cases, the primary aim is the removal of organic material, dirt or grease from surfaces to be decontaminated. Most industrial and domestic brands of soaps and detergents are satisfactory. Hot water, brushing and scrubbing enhance the cleaning action. Similarly, steam improves the cleaning and decontamination process by raising the temperature and penetrating crevices. Steam by itself can only be used as a decontaminant, however, if the temperature of the surface can be raised to 100°C and held there long enough for the inactivation of the agent. Because of uncertainties regarding temperatures and times of contact, steam is only recommended as an adjunct to decontamination in this manual.

The surfactant action of soaps and detergents is an effective decontaminant for all Category A viruses, because of their outer lipid envelope. For decontamination procedures involving exotic viruses in Category A, soaps and detergents are thus effective disinfectants in their own right.

Many commonly used disinfectants in hospitals, surgeries, dairies and food-processing areas involve soapy combinations of phenolics or quaternary ammonium compounds. These agents are specifically antibacterial and are effective against category A viruses. They have limited activity against category C viruses, however, and in many cases no activity against category B viruses. Although they may be useful for preparatory cleaning purposes during an exotic virus disease outbreak, they are not therefore recommended in this manual, because more effective cleaning agents and viral decontaminants are available.

Iodophors are combinations of solubilizing agents and a carrier that releases free iodine. It is difficult to define active concentrations with certainty in all circumstances, so iodophors are not recommended in this manual for the inactivation of viruses.

Oxidizing agents

These are the disinfectants recommended for most applications. Chlorine is released from hypochlorite solutions, either sodium or calcium, and is a powerful oxidizing agent effective in killing all virus groups (Dychdala, 1991). Scott (1980) found in test conditions that 0.175 percent sodium hypochlorite was the most effective and practical broad-spectrum disinfectant of 22 products tested against a range of different viruses. The effectiveness of hypochlorite is highest in the pH range 6–9, however, and decreases markedly in the presence of organic material. Hypochlorite powders are readily available as swimming-pool disinfectants or household bleaches and can be diluted for use on site. Hypochlorite solutions are not chemically stable and decompose rapidly as temperatures rise above 15°C.

Virkon® is a modern disinfectant with outstanding virucidal properties. Virkon® is reported to have low toxicity and to be effective against members of all 17 virus families but it has not been approved for use on skin. Its activity is based on a buffered synergized acid peroxygen system containing a high percentage of surfactant. It is relatively safe to use and comes in a powdered form ideal for dilution at the site of an exotic disease outbreak. It can be sprinkled in powdered form over wet or boggy areas but the concentration of disinfectant achieved by that kind of application cannot be accurately controlled.

Alkalis

Alkalis have long been used as effective disinfectants against a wide range of pathogens. Both sodium hydroxide (caustic soda) and sodium carbonate (washing soda) are widely available in large quantities at low cost and both have a natural saponifying action on fats and other types of organic matter, which assists the cleaning process. Because they are virucidal under heavy burdens of organic material, they are ideal agents for decontaminating animal housing, yards, drains, effluent waste pits and sewage-collection areas.

Acids

Acids are generally highly virucidal. With the correct choice of acid, or acid mixture, acids can be used under a wide variety of conditions, ranging from liquid effluent to personal decontamination. Hydrochloric acid is a strong acid, widely available from hardware stores and less toxic than other strong acids. Citric acid is a milder acid, available in solid form, that is active against acid-sensitive viruses and can be used safely for personnel and clothing decontamination. It is particularly useful when added to detergents for the inactivation of foot-and-mouth disease virus.

Aldehydes

Glutaraldehyde. A very effective disinfectant (Scott and Gorman, 1991) active against all virus families and other microorganisms in concentrations of 1 to 2 percent. It remains effective in moderate concentrations of organic material, is chemically stable and only mildly corrosive for metals. For large-scale decontamination, however, the cost is likely to be high.

Formalin. A 40 percent aqueous solution of formaldehyde gas is called formalin and is a useful disinfectant. Formalin diluted with 12 volumes of water produces 8 percent formalin, which is an active disinfectant against most virus families - but not against BSE.

Gaseous formaldehyde. Gaseous formaldehyde can be used to decontaminate air spaces, equipment such as electronic devices that must be kept dry and the insides of motor vehicles. The conditions must be carefully controlled, however, in terms of gas concentration, temperature, humidity, time of contact and even distribution of the gas. Under emergency conditions on a contaminated property, it is unlikely that all parameters can be controlled adequately. In addition, the space to be decontaminated must be completely sealed to prevent gas escape, because the most effective dwell time for inactivation is an overnight period (Quinn, 1991). Other problems with the use of formaldehyde gas for general purposes include the toxicity of gas, the dangerous nature of its generation in non-laboratory conditions (potassium permanganate reacts violently with formalin), the environmental protection guidelines that prevent the release of formaldehyde gas to the atmosphere and the difficulty of completely purging residual formaldehyde gas from confined spaces.

TABLE 4
Recommended disinfectants and concentrations for inactivation of viruses

Disinfectant groupForm1Strength2Contact time4Applications and virus category
Usual dilutionFinal3
Soaps and detergentsSolids or liquidsAs appropriate10 min Thorough cleaning is an integral part of effective decontamination.  Use for category A viruses.
Oxidizing agents:
Sodium hypochlorite NaOCIConc. liquid (10–12% available chlorine)1:52–3% available chlorine (20 000–30 000 ppm)10–30 minUse for virus categories A, B, and C. Effective for most applications except when in the presence of organic material. Less stable in warm, sunny conditions above 15°C.
Calcium hypochlorite Ca(OCI)2Solid30 g/litre 10–30 min 
Vikron®Powder20 g/litre2–3% available chlorine (20 000–30 000 ppm) 2% (w/v)10 minExcellent disinfectant active against all virus families.
Alkalis:
Sodium hydroxidePellets20 g/litre2% (w/v)10 minVery effective against virus categories A,B and C. Do not use in the presence of aluminium and derived alloys.
Sodium carbonate    
anhydrous (Na2CO3Powder40 g/litre4% (w/v)10 minRecommended for use in the presence of high concentrations of organic material.
washing soda (Na2CO3.10H2O)Crystals100 g/litre10% (w/v)30 min
Acids:
Hydrochloric acidConc. acid (10 Molar)1:502% (w/v)10 minUsed only when better disinfectants not available. Corrosive for many metals and concrete.
Citric acidPowder2 g/litre0.2% (w/v)30 minSafe for clothes and body decontamination. Especially useful for FMD virus decontamination.
Aldehydes:
GlutaraldehydeConc. solutionas appropriate2% (w/v)10–30 minExcellent disinfectant effective against virus categories A,B and C.
Formalin40% formaldehyde1:128%(w/v)10–30 minDisinfectant; releases irritating, toxic gas.
Formaldehyde gasSpecial generation required  15–24 hrToxic gas, recommended only if other methods of decontamination cannot be used.

1 Usual form supplied.
2 Recommended working strength.
3 Final concentration.
4 Required contact time for inactivation of disease agents.

Notes:

In general and unless no alternatives are available, the use of formaldehyde gas on rural properties is not recommended. Unfortunately, no satisfactory alternative to formaldehyde for gaseous decontamination is available. Use of ethylene oxide or hydrogen peroxide for gaseous decontaminations must be restricted to carefully controlled laboratory environments.

There is no simple answer to the problem of decontaminating of vehicle cabins and electronic equipment on a farm. A methodical and systematic approach based on first principles may have to be substituted. Cleaned vehicles and other machinery left in quarantine for a week in bright sunshine are likely to decontaminate naturally with respect to most pathogens. Because the parameters for effective formaldehyde decontamination are so difficult to establish on farm premises, formaldehyde gas is unlikely to produce an absolute result or be significantly more effective than thorough cleaning. Where gaseous decontamination of equipment or machinery is considered to be unavoidable, specialist advice should be sought and the contaminated equipment kept in quarantine until that time. Further information on the practicalities of using formaldehyde gas is given in Appendix 3.

Table 4 shows which disinfectant should be used for inactivating each category of virus and what dilutions/concentration should be used.

Estimation of quantities required

The amount of decontaminating agent necessary for particular jobs varies considerably. For a polished, non-porous floor, 100 ml/m3 of disinfectant/chemical is probably sufficient. For porous surfaces such as concrete or wood, however, the volume may need to be doubled or tripled.

Generalizations are not useful, because application of liquids to ceilings or vertical walls cannot be well controlled.

It is most important to remember that once a surface has been cleaned, the time it is in contact with the decontaminating agent is of critical importance. For most applications, disinfectant must flood the surface and keep it thoroughly wet for at least 10 minutes.

SAFETY PRECAUTIONS

General safety precautions First-aid boxes must be available on every IP, DCP or where hazardous chemicals are being used. Before commencing operations, it is essential to brief workers and the property owner on safety aspects, including the potentially harmful effects of chemicals on animals, humans and the environment.

The use of any chemical or equipment should conform to the manufacturer's instructions and safety standards. All officers and workers must carry out their duties in accordance with current health and safety legislation. Accidents which require medical attention, however small, must be logged and details reported back to the local disease control centre.

Acids and alkalis

When diluting concentrated chemicals, the concentrate should always be added to water, never water to concentrate. Do not mix acid and alkali disinfectants: apart from the resulting chemical reaction, the effectiveness of both chemicals is nullified. Contact with concentrates on exposed skin will cause severe burning. All workers engaged in mixing or applying disinfectants must wear boots, overalls, goggles and head covering for protection. Use a full-face guard when applying the diluted chemical. To avoid the danger of inhalation, do not apply a mist spray.

If contact occurs:

Store concentrate containers in one place on the property away from the main area of work to avoid the danger of containers being ruptured inadvertently. Check the containers each day for spillage.

Aldehydes - formalin, glutaraldehyde and formaldehyde gas

These disinfectants should be used only when no alternatives exist and only by experienced personnel with appropriate safety equipment. Gaseous formaldehyde is applicable to:

The safety of the operator is of primary importance. The method of using formaldehyde is based on safety aspects (see Chapter 4).

These substances can kill operators and even small amounts can have a detrimental effect on all living tissue. If the chemical enters the eye, a wound or an abrasion, it is extremely painful. The fumes damage all mucous membranes.

Always wear a protective face guard when mixing.

This method should only be used when it is impossible to use other procedures.

Warning notices should be fixed to the entrance of an area being fumigated. There should be two people involved in the operation - both equipped with full-face respirators effective against formaldehyde gas.

TABLE 5
Special considerations when using disinfectants

DisinfectantHealth aspectsEnvironmental problems and contra-indications
HypochloritesToxic for eyes and skin.Strong bleach. Inhibited by high concentrations of organic matter, Corrosive for many metals.
Virkon®Reasonable care necessary. 
Sodium hydroxideCaustic for eyes and skin.Avoid contact with strong acids. Cannot be used on aluminium or similar alloys.
Sodium carbonateMildly caustic for eyes and skin.Avoid use with aluminium and similar alloys.
Hydrochloric acidToxic for eyes, skin and respiratory passages.Corrosive for concrete and many metals. Avoid contact with strong alkalis.
GlutaraldehydeAvoid eye and skin contact. 
Formalin solutionReleases toxic gas; irritating for mucous membranes. 
Formaldehyde gasVery toxic for mucous membranes in concentrations down to 2 ppm.1Cannot be used in presence of water, hypochlorites or chlorides. Cannot be released to atmosphere without neutralization. Corrosive for some metals.

1 ppm = parts per million


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