Contagious Bovine Pleuropneumonia (CBPP) is one of the major diseases threatening cattle raising in Africa. Earlier this century it was widespread in the pastoral areas of east and west subsaharan Africa but control measures including vaccination campaigns successfully eradicated the disease from most of the continent so that by 1970 CBPP was largely confined to the horn of Africa, some parts of the West African Sahel and Angola.
Civil disturbances in Ethiopia and Sudan have subsequently reduced the effectiveness of these control measures (particularly control of the movement of livestock) and in the last decade the disease has spread back into Uganda, Rwanda, Kenya and Tanzania. During the last 12 months (1994–95) infected animals have moved along trade routes into southern Tanzania and outbreaks of disease have occurred there which threaten Zambia, Zimbabwe, Malawi and Mozambique. On the other hand civil disturbances in Angola have led to the migration of infected cattle from that country into Namibia, and very recently, across the Caprivi strip into Botswana.
CBPP is an insidious disease that may not be detected for several weeks or months after infected animals have entered an area and so the present situation may be even more serious than reports suggest. If the disease is not to make further advances into Southern Africa the following measures must be taken:
a cordon sanitaire (buffer zone) established to separate the infected and the threatened territories
control programmes developed in the infected areas
disease preparedness measures initiated in those areas that are presently clear of the disease but are under threat
This paper outlines the concept of a CBPP control and eradication programme for Africa that incorporates these measures. The recommendations conform with the proposals for the control of CBPP agreed at a meeting of the subcommittee of the FAO/OIE/OAU expert panel on CBPP (Lagos 1970) and the OIE recommended standards for epidemiological surveillance systems for CBPP (appendix V of the 63rd General Session of the OIE, 1995). It is also in line with the recommendations of the FAO - EMPRES Workshop on the subject convened jointly by FAO,OAU and the Tanzania Government, at Arusha, 4–6 July 1995.
1 EMPRES/Infectious Disease Group, Animal Health service, FAO, Rome (Prepared with the collaboration of Drs. Alain Provost and Gareth Davies as FAO Consultants, November 1995)
2. A CORDON SANITAIRE (BUFFER ZONE)
The objective of a cordon sanitaire is to block the movement of infected cattle into clean areas. This is achieved by employing some or all of the following control methods:
controlling movements along recognised trade routes to prevent the spread of infection
slaughtering infected herds to remove existing foci of disease
vaccinating the cattle population (blanket vaccination) to prevent the development of further outbreaks
A cordon sanitaire across Africa must be established as soon as possible so as to protect livestock in Southern Africa. This cordon will be in two parts:
an eastern buffer zone covering the international borders between Tanzania and Zambia, Malawi, and the area of Zaire immediately to the west of lake Tanganyika
a western buffer zone stretching from the Atlantic Coast across northern Namibia, northern Botswana and western Zambia.
The territories to be covered by these zones are shown in the attached map (Annex 1)
It is proposed that these buffer zones shall have two components:
a surveillance zone at least 50 km deep covering the disease - free side of the international border. Within this zone control will be enforced by
The livestock in this zone will not be vaccinated as this will mask the presence of the disease.
a control zone at least 100 km deep covering the infected side of the border (and immediately adjoining the surveillance zone). Control will be maintained in this area by
2.1. ACTIONS IN THE SURVEILLANCE ZONES
2.1.1 Movement Control
No animals will be allowed over the international border (or the border of the surveillance zone facing the infected area where that border is not an international border) without a movement permit issued at the point of departure and declaring that the herd of origin has been inspected and is free of clinical CBPP. The animals must be vaccinated (and marked accordingly) at source not more than three months prior to movement.
The movement of cattle into or across the surveillance zone should be confined, as far as possible, to stock destined for immediate slaughter. The movement of breeding cattle is inadvisable and should be discouraged.
All consignments of animals crossing the zone must be examined for clinical evidence of disease. Where animals are moved in vehicles (road or rail) they must be disembarked to allow for inspection.
All movement of cattle across a surveillance zone should be through recognised quarantine stations that have facilities (holding areas) for disembarked cattle.
2.1.2 Intensive Surveillance
Abattoir Surveillance - All abattoirs in the zone must be kept under surveillance for carcasses containing CBPP lesions. Meat inspectors must be trained to recognise the lesions and take the appropriate samples.
Field Surveillance - All herds in the surveillance zones should be inspected at intervals of not more than two weeks. Inspections should take advantage of cattle gatherings at diptanks etc. Dead animals should be post mortemed and if CBPP is suspected, simple serological tests carried out in the field to be followed by confirmatory tests at diagnostic laboratories. All village slaughter slabs should be inspected regularly.
2.2 ACTIONS IN THE CONTROL ZONES
The objective of the control zone is to limit or prevent incursions of disease into the surveillance zone. The actions to be undertaken in the control zones are:
All cattle in the zones to be vaccinated twice at three monthly intervals and thereafter annually with vaccine that contains at least 108 CFU per dose. Vaccination to be compulsory and therefore free of charge on the grounds that vaccination is being undertaken primarily to protect and benefit animal populations in the disease free areas of Southern Africa.
All herds to be inspected monthly
2.2.3 Movement control
All herds moving into the control zone must be vaccinated at source and marked accordingly.
2.3 RESOURCES REQUIRED TO MAINTAIN THE CORDON SANITAIRE
2.3.1 Quarantine stations
2.3.3 Field Surveillance
2.3.5 Diagnostic Facilities
Preliminary diagnosis (gross pathology and the simpler serological tests) can be undertaken in the field. Back-up diagnostic facilities (CFT and cultural examinations) should be provided by provincial and national laboratories preferably located within or close to the zone.
2.4 OUTBREAKS OF CBPP WITHIN THE BUFFER ZONE
2.4.1 The surveillance zone
If an outbreak of CBPP occurs within the surveillance zone the affected herd should be slaughtered (and the owners compensated). The source of infection must be traced and contact herds tested. If further infected herds are detected they must be slaughtered but if it is clear that to continue this strategy is untenable the surveillance zone must be converted into a control zone and new surveillance zone demarcated.
2.4.2 The control zone
If an outbreak occurs in the control zone the clinically affected cattle should be slaughtered and the survivors vaccinated and quarantined. Surrounding herds should be inspected and if clear of clinical disease revaccinated.
3. ANTIBIOTIC TREATMENT AS A MEANS OF CONTROLLING INFECTION IN THE SURVEILLANCE ZONE
Cattle incubating CBPP are almost impossible to detect and the incubation period may last several months. These incubating cattle present a considerable risk during cattle movements.
Vaccinating cattle during the incubation stage of the disease may not extinguish the infection and a more certain alternative way of dealing with the risk is to treat the cattle with antibiotics.
Whilst widespread antibiotic treatment is not to be recommended in infected areas where cattle are vaccinated (see Annexe 2) consideration should be given to the antibiotic treatment of all cattle leaving the surveillance (non-vaccinated) zone for the clear areas.
4. THE INFECTED AREAS
CBPP is widespread in large areas of Kenya, Uganda, Rwanda (and possibly Burundi), eastern Zaire, Tanzania, Angola, Ethiopia and the southern Sudan. In some of these countries e.g. Ethiopia, Sudan, and Angola, the disease is long established and can be considered endemic whereas in Tanzania, Namibia and Botswana CBPP is a recent importation and is more sporadic.
5. PRIORITIES WITHIN THE INFECTED AREAS OF AFRICA
Eradicating the disease from all these countries is a long-term prospect and priorities should be established if the available resources are not to be overwhelmed. The first priority should be given to campaigns in infected countries that present an immediate threat to the clear areas.
|Priority 1||-||Tanzania, and Botswana-to protect Southern Africa.|
|Priority 2||-||Uganda (except Karamoja), Rwanda, eastern Zaire and southern Kenya-'to protect Zaire and Burundi.|
|Priority 3||-||A'ngola and northern Namibia - to protect Namibia, Zambia and Botswana.|
|Priority 4||-||Ethiopia, Sudan, northern Kenya and Uganda (Karamoja).|
6. PRIORITIES WITHIN INFECTED COUNTRIES
Some of the infected countries are large e.g. Tanzania which has 13 million cattle; and in conducting an eradication campaign certain priorities should be allocated to the various areas within the countries as follows:
|Priority 1||-||Infected areas which export cattle to the other parts of the country or to neighbouring countries.|
|Priority 2||-||Areas where the cattle populations appear to be free of CBPP but which receive cattle from other areas and are therefore under threat.|
|Priority 3||-||Areas where the livestock industry is self-contained and where there is little movement of animals.|
Particular attention should be paid to controlling disease along livestock trading routes.
7. ACTIONS WITHIN THE INFECTED COUNTRIES
7.1 General Principles
The traditional methods of controlling and eventually eradicating CBPP are:
(where possible) slaughter of infected herds
In the present circumstances in Africa the effective deployment of all three methods is difficult and in some cases impossible. Livestock owners may be reluctant to accept movement controls and the necessary (police) forces may not be available to enforce them. Vaccination is acceptable provided that there be no untoward losses post vaccination but to achieve good vaccination cover of the population requires careful planning and execution. The slaughter of infected herds is unacceptable to most livestock owners unless there is immediate and full compensation and compensation payments are costly to the authorities.
Whilst recognising that the effective deployment of control measures may pose severe problems to the authorities certain standards must be achieved if control is to succeed (these are underlined below) anything less is a waste of valuable resources.
7.1.1 Movement Controls
CBPP is spread by direct close contact between animals and epidemics if the disease are entirely due to the movement of infected livestock. These movements must be controlled and by three methods:
The quarantining of infected herds until the infection has died out. This may take several months.
Controlling long distance movements of livestock. by ensuring that cattle do not move without health certificates (indicating that they have been examined and are free of clinical disease) and vaccination certificates (indicating vaccination within the last 3 months).
Controlling local movements e.g. transhumants by identifying areas within which cattle may move freely but which they can not move out of.
CBPP Vaccination of individual animals increases their resistance but may not prevent them becoming infected. Vaccinating whole populations will gradually extinguish infection circulating in that population but only if vaccination cover approaching 100 % is achieved. Anything less means that there is the risk of susceptible (non vaccinated) cattle contracting the disease and by close contact with vaccinated stock overcoming (vaccinal) resistance. In such a situation the livestock owners and the authorities lose faith in the vaccination campaign and it fails.
7.1.3 Slaughter of Infected Herds
This is the quickest way of eradicating the disease provided it is accompanied by effective movement control. Herds containing clinically affected cattle are identified by inspection and subclinically infected livestock detected by serological tests. The cost of these measures means that slaughter should be a strategy of last resort to be used in critical epidemiological situations e.g. in the case of outbreaks in the free area or the surveillance zone (of a cordon sanitaire) or on major trade routes.
8. ENFORCING EFFECTIVE STANDARDS
National authorities planning CBPP control and eradication campaigns should ensure that certain minimum standards are planned for and achieved (particularly regarding vaccination cover). Donor organisations should likewise ensure that certain standards are implicit in the plans that they support. A national veterinary authority with a clear chain of command should be a prerequisite.
9. THE DISEASE-FREE TERRITORIES (countries or epidemiologically distinct zones within a country)
Large areas of southern Africa are free of CBPP but are under threat from movements of cattle from the north. Because the disease has been absent from these territories for a long time livestock owners and others in the livestock trade they may not be aware of it. Veterinarians and other who inspect live cattle and carcasses may not be familiar with the diagnostic signs of CBPP and may not know what action is to be taken when it is detected.
To correct these deficiencies the authorities in the disease-free territories should amount a campaign of disease awareness and develop surveillance systems and contingency plans.
10. DISEASE AWARENESS
Veterinary authorities should ensure that livestock owners are made aware of the threat of CBPP by local contact between farmers and veterinary staff and by using the national and local media. Video presentations and other aids should be developed.
11. SURVEILLANCE SYSTEMS
The best way of detecting CBPP is by abattoir inspection of cattle lungs. All abattoirs should have meat inspectors trained to recognise CBPP lesions and instructed to send, on suspicion, appropriate samples to a nominated diagnostic centre. In addition veterinary staff should inspect village slaughter slabs at regular intervals.
Veterinary and other staff who supervise the collection of cattle at diptanks should be trained to recognise the signs of the disease.
The veterinary authorities should develop appropriate monitoring systems that cover all the above information points.
12. CONTINGENCY PLANNING
All veterinary authorities should draw up contingency plans for action in the event of an outbreak of CBPP. Model plans have been developed for FMD by the European Union and FAO and these can be adopted to the circumstances of the individual country and the epidemiological characteristics of CBPP.
13. FUNDING THE CAMPAIGNS
The actions outlined in this paper fall into three categories:
actions in the cordon sanitaire - these are urgent
actions in the infected territories - planning should start immediately with a view to decisions being taken in the next few months.
actions in the disease free territories - these are a matter for the national authorities concerned (with advice from international experts)
The geographical area covered by these actions fall within the orbit of:
SADC - covering southern Africa
PARC - covering eastern and western Africa
The area covered by SADC includes the proposed cordon sanitaire and the infected areas in Botswana, Namibia, Angola and Tanzania. The cordon sanitaire is designed to protect the whole of southern Africa and the burden of funding and maintaining it should not rest solely with the local authorities. A cooperative effort is required by all the national and regional administrations in southern Africa.
The area covered by PARC includes most of the infected areas and thought should be given to making use of the administrative arrangements (and funding) developed for Rinderpest eradication.
14. COST RECOVERY
It is recognised that control and eradication schemes should include an element of cost recovery so as to lessen the burden on donors and also to involve the livestock industry. Cost recovery is always difficult to achieve in subsistent agriculture and it is particularly difficult in the case of CBPP eradication. Success depends on achieving total vaccination cover of the livestock population at risk and this is not possible if the livestock owners are charged for vaccination. If funds have to be raised out of the campaign they should be raised by some form of general levy.
Traditionally, the control of epidemic diseases of livestock has been the preserve of government veterinary services staffed by full time employees. Some animal health support to the livestock industry is now being provided by veterinarians and others in the private sector and the implementation of a major CBPP Control campaign provides the opportunity to encourage this development. The private sector should be offered sufficient incentive that will encourage it to undertake much of the routine vaccination and surveillance work but under the control of a designated group of public sector veterinary inspectors. It is essential that the campaigns are planned and supervised by the government services. This should lead eventually to government veterinary services with reduced staff numbers but increased skills in the field of strategic planning, surveillance, epidemiology and diagnosis. Consequently the CBPP control campaign should make a significant contribution to the evolution of effective national veterinary services with a synergistic balance between the public and private veterinary sectors as depicted in the attached chart (Annex 3).
16. A COMMAND STRUCTURE
The area to be covered by this programme is too large and too politically and socially diverse to be managed by one central unit. It is proposed that there should be two coordination units.
A unit associated with PARC and responsible for CBPP control and eradication in the Sudan, Ethiopia, Kenya, Uganda, Rwanda, Burundi, eastern Zaire and northern Tanzania as far south as just beyond Central Railway line (Dar es Salaam to Kigoma). This territory covers most of the infected areas.
A unit associated with SADC responsible for the southern part of Tanzania (up to the central railway line), Malawi, Mozambique, Zambia, Anola, Botswana and Namibia. This territory covers the two cordon sanitaires and the disease free areas under threat.
Each Regional Unit should be staffed by a Manager assisted by an epidemiologist, a Veterinary logistics specialist and the necessary financial and administrative support. In addition each unit should be supported by consultants in laboratory diagnosis, public awareness (communication) and other relevant short term specialist inputs.
CBPP SANITARY CORDON AND ZONATION IN EASTERN, CENTRAL AND SOUTHERN AFRICA
17. THE USE OF ANTIBIOTICS TO CONTROL CBPP
Mycoplasma mycoides, the agent of CBPP, is susceptible to a range of antibiotics and there is no doubt that owners of infected animals sometimes treat them.
Little research work has been carried out on the effect of antibiotics on the pathogenesis of the disease but it is likely that the sequence of events is as follows:
Treatment during the incubation period (before clinical signs) - treatment should kill the causative organism and it may be that a single treatment is sufficient. The animal will recover but may not develop resistance to the disease nor develop a serological response.
Treatment of clinical cases- early clinical cases may respond to prolonged treatment but advanced cases may not. In both cases, if the animal survives, it is possible but not certain that the treatment will result in a chronic carrier condition. The consensus is that such animals will not easily be detectable by serological test.
Treatment of chronic case or “lungers” - the consensus of opinion is that treatment will have little effect on these cases as the causative organism, if present, is walled up in the sequestrum.
Treatment of vaccinated animals - treatment in recently vaccinated animals will kill the vaccine strain and thus abort the development of immunity. Animals vaccinated sometime in the past will have little remaining resistance and can be regarded as susceptible animals.
The conclusions must be that treatment is only of value if cattle are in the incubation stage and is contraindicated if they have been recently vaccinated. It follows that treatment maybe of value in two particular situations:
Where cattle are moving from infected areas into free areas (but only when the herd of origin is disease free). Some may be incubating the disease and treatment of all animals in the herd may abort the epidemic.
An outbreak of disease where cattle are quarantined awaiting for slaughter. Some of the cattle will be advanced cases and will die, but others will be incubating the disease. In the normal course of the events some of these will eventually die and some will become “lungers”. This sequence of events may be aborted by treating the cattle that are not clinical cases. This course of action may be of particular value in reducing the cost of an outbreak where the herd is destined for slaughter and the meat of the survivors has a salvage value.
AN ILLUSTRATIVE NORMOGRAM FOR A NATIONAL VETERINARY STRUCTURE
* To include all organisations (predominantly private) set up for the provision of clinical services even if for “temporary” socio-economic reasons there may be need for direct governmental participation.