This Manual mainly addresses the situation where CBPP invades a country, or a zone within a country, that was formerly considered free from CBPP. Should such an emergency occur, all initiatives would be directed at rapid containment of the disease to the primary focus or zone of infection, and eradication within the shortest possible time to avoid spread and possible progression to endemic status.
However the same principles for control and eradication are also very applicable to dealing with the situation where CBPP is already endemic in part or all of the country.
There are a number of epidemiological and other factors - some favourable and others unfavourable - that need to be taken into account when devising eradication strategies for CBPP. These include:
- no domestic livestock species other than cattle and water buffaloes (and yaks in the restricted regions where they occur) are susceptible to CBPP; humans are not susceptible;
- there are no wildlife reservoirs of infection;
- MmmSC is closely related to other mycoplasmas in the ‘mycoplasma cluster,’ complicating its identification;
- CBPP is transmitted by close direct contact between animals, and thus movement of infected cattle and congregation of animals is the key factor in its spread;
- the causal organism survives poorly in the environment and therefore indirect spread of infection, e.g. by fomites, is unimportant;
- epidemics in new areas sometimes evolve slowly, making early detection difficult;
- cattle that survive CBPP infection are likely to become chronic carriers, with sequestered lesions in their lungs. A proportion of these are seronegative. Sequestra may break down, particularly when cattle are stressed, and these animals again become active spreaders of infection;
- vaccines that are available are far from perfect. Nevertheless, vaccination campaigns, if comprehensively and consistently applied, are a valuable component of control and eradication campaigns; and
- the use of antibiotics, whilst ameliorating clinical signs in acute cases, may complicate eradication programmes, with the possible creation of chronic carriers of the disease.
Some of these factors, particularly the presence of chronic carriers and problems in disease surveillance, make CBPP one of the more difficult transboundary animal diseases to eradicate. Nevertheless, it has been eradicated, often under difficult circumstances. For example, it was eradicated from Australia by comprehensive vaccination campaigns, zonation, movement controls and final stamping out. It was eradicated from Botswana much more quickly by stamping out.
Taking account of the above epidemiological and other factors, there are three broad strategies for the control and eradication of CBPP, namely:
- reduction in the number of infected and potentially infected animals in cattle populations through stamping-out campaigns;
- reduction in the rate of direct contact between infected and susceptible cattle through surveillance programmes, zonation, quarantine and strict movement controls; and
- reduction in the number of susceptible animals in target populations through comprehensive vaccination campaigns.
Stamping out is certainly the most rapid and effective method of CBPP control (as it is for many other transboundary animal diseases), and international recognition of disease-free status can be more quickly regained for export trading purposes (see Appendix 3) if stamping out is applied. It is also likely to be the preferred option for dealing with isolated outbreaks in developed countries. However, it is seldom a practical or economically viable proposition for developing countries. The exceptions are:
- when an outbreak of CBPP in a previously free country or zone of a country can be detected quickly whilst it is still localized, and the infected area can be accurately identified and sealed off; and
- during the final mopping-up stages of an eradication campaign, when there are only a few isolated incidences of the disease.
Comprehensive vaccination campaigns are likely to be an integral part of most CBPP control and eradication programmes. They are important in reducing the incidence of the disease to a very low level, where other control and eradication options become more viable. However vaccination alone will not guarantee eradication, and in the long run may be very costly.
Strategic planning for the control and progressive eradication of CBPP, whether it is preparedness for the disease in a free country or if it is to eradicate the disease in a country where it already occurs, most often involves a structured approach that incorporates each of the three broad control and eradication strategies described above.
This structured approach involves progressive application of the following measures:
- immmediate zoning of the country to take account of the known and suspected locations of the disease;
- instigate quarantine and cattle movement controls that will minimize spread of infection and prevent spread outside the designated infected zone;
- instigate a comprehensive disease surveillance programme for CBPP throughout the country - with adjustment of infected, control and free zones according to findings;
- make the decision as to whether or not to proceed with a stamping-out programme, based on analysis of epidemiology, socio-economics and resource availability;
- if stamping out is not selected, undertake a comprehensive vaccination programme for a minimum of three years, and more probably for five years. In the case of countries where CBPP is endemic, the vaccination programme would probably need to cover the whole country;
- cease vaccination when the disease incidence has fallen to an acceptably low level;
- instigate a disease surveillance programme that will lead to a progression from provisional declaration of freedom from disease, to freedom from clinical CBPP, and finally freedom from CBPP (see Appendix 3); and
- have preparedness plans to respond very rapidly to any disease breakdowns, applying either stamping out (preferable) or targeted vaccination and movement controls.
The epidemiological nature of CBPP, where there will be persistence of infection and transmission of the disease (often over long distances) through subacute and chronic cases, dictates that, to be successful, control and eradication programmes must be both comprehensive and consistently applied over a number of years.
Equally, a piecemeal approach to CBPP control and eradication is almost certainly doomed to failure. It will condemn countries to CBPP endemicity, discourage both animal health officials and farmers, and make eventual eradication both difficult and costly.
In many areas where CBPP currently occurs or which are at high risk of the disease, the potential natural epidemiological range of the disease extends over territory that may encompass more than any one country and may indeed include several countries. This may occur where there are traditional cattle trading, herding, nomadic or transhumance patterns that extend over a large region. Examples of this are to be found in the well-recognized ecological zones for CBPP in West and Central Africa; eastern Africa; and southern Africa.
Significant progress towards CBPP eradication in these ecological zones will only be possible if there is a high degree of cooperation between neighbouring countries in the development and implementation of regionally coordinated CBPP prevention, preparedness and control and eradication programmes.
Whilst penicillin and its analogues are ineffective, a number of broad-spectrum antibiotics are mycoplasmacidal. Such antibiotics may ameliorate the clinical signs of CBPP. However, they do not necessarily eliminate infection in treated animals. This makes control and eradication of the disease in endemic areas more difficult and increases the risks of spread of the disease to new areas. Since most farmers treat their cattle infected with MmmSC with antibiotics in any case, a structured scientific study on the effect of various types of antibiotic treatment on the course of CBPP disease is needed. This will provide the scientific basis for the rational use - or otherwise - of antibiotics in CBPP control.
When CBPP is detected in a previously free country or region of a country, the first step to be taken is to immediately quarantine the known affected farms to prevent the movement of potentially infected cattle from these farms. An urgent epidemiological assessment is then undertaken to make an initial estimate of the likely spread of infection that has taken place. This would be based not only on the sites of known disease occurrence, but also on movements of cattle to and from these sites and on opportunities that have occurred for mingling of infected and susceptible cattle.
Based on this initial assessment, three zones would be declared: infected zones; surveillance zones; and CBPP-free zones.
The infected zone encompasses the area immediately surrounding one or more infected farms, premises or villages. Whilst its size and shape is influenced by topographical features, physical barriers, administrative borders and epidemiological considerations, OIE recommends in general that infected zones should be at least a 10 km radius around disease foci in areas with intense livestock raising, and 50 km in areas where extensive livestock raising is practised.
In the initial stages of an outbreak, when its extent is not well known, it would be wise to declare larger infected zones, and then progressively reduce these in size as active disease surveillance reveals the true extent of the outbreak.
There should be a complete ban on the movement of cattle out of the infected zone, and this should be rigorously enforced.
The chosen disease control strategy, whether it is stamping out, vaccination or a combination of these, is then instituted.
This zone is much larger, and surrounds one or more infected zones. It may cover a whole Province or administrative region, and, in many cases, the whole country. In this zone, the most intensive disease surveillance is carried out. Cattle should not be allowed to move out of this zone unless they are moving directly under supervision to abattoirs for slaughter or are shown by testing to be free of infection.
This encompasses the rest of the country. However, because of the potential of CBPP for wide dissemination, it would be unwise to regard any part of a country in the throes of a virgin outbreak as unworthy of a high level of surveillance. The emphasis in free zones should be on strict quarantine measures to prevent entry of the disease from infected zones, coupled with continuing surveillance to provide confidence of continuing freedom. These zones should be subjected to the same degree of information dissemination as the zones in which the outbreak occurs. This should be extended, through good and rapid communication, to neighbouring countries.
Comprehensive disease surveillance programmes should be put into place throughout the country, and the zones should be progressively adjusted according to findings.
A stamping-out programme for CBPP involves the destruction of all infected and potentially infected cattle in well-defined infected areas, combined with very strict movement controls to ensure that cattle cannot leave the target areas.
Careful socio-economic and resource availability analyses should be carried out before a decision is made to embark upon a stamping-out campaign. As has already been noted, stamping out is only likely to be a viable proposition under certain circumstances, including:
- when the disease is detected early after its introduction into a previously free country or area, and it is still limited to relatively small and well-contained geographical areas and cattle populations;
- during the final mopping-up stages of a control and eradication programme to deal with small, isolated disease outbreaks; or
- when the need to re-establish export markets dictate that stamping out should be used so that the country can gain quicker recognition of disease-free status and thus access to markets.
A stamping-out campaign should not be undertaken unless essential prerequisites can be met (see Box 1).
An early decision will need to be made whether to slaughter all cattle within the designated infected area(s), or only those on farms where the disease is detected either on clinico-pathological grounds or by other surveillance procedures (including serological testing). Because of the difficulties in maintaining a high enough level of surveillance and in preventing mixing of cattle between farms, the decision is usually taken to slaughter all cattle within the designated infected area.
Destruction of cattle would normally be by humane shooting, either by firearms or captive-bolt pistols. This is described more fully in the FAO Manual on Procedures for Disease Eradication by Stamping Out (FAO Animal Health Manual, No. 12).
As the causative organism, MmmSC, is not transmitted in meat, consideration could be given to salvaging meat by allowing clinically healthy cattle to be transported for immediate abattoir slaughter, providing this is done in controlled abattoirs with meat inspection within the infected area.
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Box 1. Essential prerequisites for a CBPP stamping-out campaign
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There is no need to dispose of the carcasses of slaughtered cattle by deep burial or incineration for reasons of preventing further CBPP transmission (as would be the case for diseases such as foot-and-mouth (FMD)), although some disposal process may be desired on environmental, public health or aesthetic grounds. Likewise, there is no need to clean and disinfect infected properties after de-stocking, as would be the case for other TADs where there is longer survival of the agent in the environment and there is transmission by fomites.
Restocking should not commence until it can be assured that all infected and potentially infected cattle in the target area have been slaughtered. In areas where there is poor control of cattle or difficult terrain, it may be necessary to supplement ground searching by aerial surveys, and to remove cattle in inaccessible locations by shooting from helicopters. In some instances, monetary incentives for finding cattle during the mop-up phase have been useful in locating and destroying cattle that might have been missed during the initial destruction phase.
It would be usual practice to leave areas for 3 to 6 months (depending on circumstances) before restocking, to be on the safe side. Restocking must be done with known CBPP-free cattle, preferably from a free zone. Serological testing (CFT and c-ELISA) to confirm freedom from infection would be the ideal. The opportunity could also be taken for genetic upgrading.
Vaccination programmes as components of a CBPP eradication campaign must be comprehensively and consistently applied until there is evidence from disease surveillance that the disease has either apparently disappeared or at least the incidence has fallen to an extremely low level. The target areas for vaccination should include all but proven CBPP-free zones. In endemic regions, countrywide programmes are usually needed.
Live, attenuated CBPP vaccines are used. These may involve some compromise between inocuity and immunogenicity. Vaccine strains that are currently in use are T1-44 and T1-SR. T1-44 is currently the preferred vaccine in most countries. However, it has been criticized in some countries for causing excessive local reactions in vaccinated animals.
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Box 2. Compensation It is essential that farmers and other persons who have had their cattle slaughtered should be fairly compensated for their current market value. This compensation should be paid without delay. Valuation for compensation purposes should be undertaken by experienced, independent valuers. Alternatively, generic valuation figures could be agreed upon for specific categories of cattle. At least the market value of the cattle should be paid. Under some circumstances, replacement of stock might be offered in lieu of monetary compensation. Failure to pay adequate and timely compensation would seriously compromise CBPP eradication campaigns by causing resentment in communities, lack of cooperation and would act as a spur to the illegal smuggling and clandestine sale of cattle out of infected areas to avoid losses. |
It is essential that vaccine be procured from reliable manufacturers (i.e. those with external quality assurance certification) who adhere to internationally recognized standards of good manufacturing practice and quality assurance for vaccine seed management, viable mycoplasma titre, purity, safety and potency. These standards are to be found in section 2.1.6 of the OIE Manual of Standards of Diagnostic Tests and Vaccines (see www.oie.int).
Freeze-dried vaccine is usually used. However it is essential that adequate cold-chain facilities are available at central and local vaccine storage depots, and from there to the points of injection in the field.
The limitations of current vaccines should be recognized. Primary immunization protects substantially less than 100% of the vaccinated population and immunity in many cattle lasts less than one year. Furthermore, vaccination will not necessarily eliminate infection in animals already infected, particularly carrier animals. Both the immune coverage and duration of immunity improve markedly on subsequent vaccinations. Despite these limitations, vaccination systematically applied to target cattle populations with as close as possible to 100% coverage for several years will have a dramatic effect on reducing the incidence of the disease to very low levels in infected areas.
During the initial stages (first year or two) of a comprehensive vaccination campaign, cattle should be vaccinated at intervals of 4 to 6 months. Thereafter, annual vaccination is generally sufficient. The vaccination programme must be maintained for at least 3 to 5 years, or until the disease can no longer be detected by surveillance (e.g. clinical, abattoir, serological).
Untoward vaccination reactions are more liable to occur in Bos taurus breeds than in Bos indicus. These may take the form of severe local reactions, and very occasional systemic reactions and even death. Adverse reactions can be minimized by attention to correct vaccination technique. CBPP vaccines must be injected subcutaneously (not intramuscularly, intradermally or into fascial sheets). The preferred site is in the neck, although tail vaccination is also used.
Vaccination teams, whether in the public or private sector, must be trained in the proper storage and handling of CBPP vaccines and in proper vaccination techniques. Furthermore, good facilities need to be provided for restraining cattle during vaccination.
Cattle that have been vaccinated ought to be identified as such. A consistent, permanent identification system for vaccinated cattle needs to be provided within the country. This should indicate how often, and preferably also when, the cattle have been vaccinated. A system of ear marking or notching may be adequate for this purpose.
This is often the most critical phase of the eradication campaign. This occurs when the clinical disease has apparently disappeared. If the wrong actions are taken at this stage and undetected pockets of infection remain, many of the benefits that have accrued from the eradication campaign may be eventually lost.
Governments may make one of two potentially bad decisions at this stage, unless they are properly advised.
The first is that they may decide that now that the clinical disease has waned or disappeared, then the socio-economic losses are over and the scarce financial and other resources being expended might be better diverted elsewhere. If disease control activities are prematurely wound down, leaving undetected infection, the disease is likely to flare up into further serious outbreaks as immunity levels in animal populations decline.
The second possible government decision, at the other end of the spectrum, is that routine vaccination programmes should be maintained indefinitely because of the fear of the political consequences if vaccination were stopped and there were then another outbreak. In this case, there will be a continuing economic burden from the control costs.
In both cases, the export trade opportunities that may flow from having an internationally recognized disease-free status will not be available.
When the clinical disease appears to have disappeared from either a region of a country or the whole country, it is time to take stock of the situation and to carry out a thorough epidemiological and economic assessment of future options.
It may well prove desirable to maintain strategic vaccination in high-risk areas if there is still a very high threat of a new incursion of the disease, such as from a neighbouring country. At the same time, it is in many cases very advantageous to completely change tack by stopping vaccination programmes all together and moving to a disease search-and-destroy policy. This does not necessarily mean that fewer resources will be devoted against the disease in the short term. Rather, they will be directed away from routine vaccination toward increased activities focusing on early warning and early response. There must be a willingness to enhance active disease surveillance activities and to maintain at a high level preparedness against the disease. In this way, any disease breakdowns can be detected and eliminated quickly.
It should then be possible to proceed down the pathway that will allow OIE declaration of provisional freedom from disease, to final freedom from CBPP. The level of disease surveillance required in the final stages of eradication and for the necessary OIE declarations are shown in Appendix 3.
If any breakdowns are detected during this final stage of the eradication campaign, the disease should preferably be eliminated by stamping out. The need for early detection is vital if this is to be done. Alternatively, consideration could be given to slaughter of clinically diseased animals and animals that test positive to the disease, combined with an intensive vaccination campaign for surrounding cattle herds, with strict quarantine and movement controls.
