1. INTRODUCTION
Contagious bovine pleuropeumonia (CBPP) epidemiology is characterised by the following: (1) transmission by direct contact; (2) long incubation period; and (3) possibility of early excretion of mycoplasmas (up to 20 days before apparition of clinical signs), during the course of the disease and after recovery in “lungers” (up to two years). These epidemiological features on the one hand, and the lack of a reliable screening test to pick up early carriers and lungers on the other hand, make it essential to control cattle movements in order to limit the spread of the disease.
Provided that control of animal movements is at hand, CBPP is eradicable using either a stamping out strategy (elimination of the whole herd) or, more realistically under African conditions, a combination of quarantine and repeated vaccination. Such measures must be maintained until evidence of CBPP eradication is demonstrated by structured surveillance as proposed by the OIE pathway. Currently, two types of live attenuated vaccines are available: one is the conventional T1 strain and the other is a streptomycin-resistant mutant of the former (T1-sr). T1-sr offers the advantage of its possible use in combination with the rinderpest vaccine in areas where immunisation against both diseases is recommended.
2. GOALS
Despite fundamental differences in the epidemiology of the two diseases and disparity of available means and tools for combating them, CBPP has long been treated as a mere component of rinderpest control/eradication programmes (epidemiosurveillance based on seromonitoring, CBPP vaccination generally using combined vaccine and restricted to areas where rinderpest vaccination is planned, sometimes annual vaccination focusing on immunisation of young calves only,etc.).
Attitudes must now change and the implementation of a CBPP global control strategy should start with a view of eradicating the disease from the recently infected areas (essentially in eastern and southern Africa) and then from the endemic zones. The length of such a programme will depend among others on the amount of efforts devoted to control animal movements.
These goals will be more readily and effectively achieved if, meanwhile, a diagnostic/screening test which is more sensitive than the complement fixation test (the current OIE reference test) is developed as well as a vaccine conferring long lasting immunity.
3. STRATEGIES
The most urgent task is the definition of endemic areas, epidemic and at risk zones as well as setting up a structured surveillance system in order to be able to define cost effective control strategies. EMPRES, in collaboration with OAU IBAR and SADC in Africa and possibly APHCA in Asia could assist in this activity.
The availability and quality assurance of the required amount of CBPP vaccine must be secured and, again this responsibility could be taken over by EMPRES in collaboration with PANVAC.
In addressing the CBPP issue one should necessarily address the problem of veterinary services structure and their ability to implement effective control measures as well as control of animal movements.
CBPP control strategies have recently been reviewed by EMPRES with particular emphasis on eastern, central and southern Africa. Conceptually, the area may be divided into three epidemiological categories:
the free areas where emphasis has to be placed on enhanced surveillance and CBPP emergency preparedness;
the infected areas where intensified control action needs to be instituted relying on either a slaughter policy or a prolonged quarantine and systematic vaccination policy; and
the cordon sanitaire sufficiently defined to separate clean and infected areas.
This cordon is envisaged to 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, the northern Bostwana/Namibia border and the western Zambia/Angola border.
These buffer zones will each have two components: (a) a surveillance zone at least 50 km deep covering the disease-free side of the international border in which no vaccination will take place while intensive surveillance and animal movement control will be enforced; and (b) a control zone at least 100 km deep covering the infected side of the border immediately adjoining the surveillance zone. Control will be maintained in this area by: intensive vaccination, surveillance and movement control.
A similar detailed analysis of the CBPP problem is needed for West and Central Africa as well as for the Horn of Africa and for the CBPP affected zones in Asia.
4. PROPOSED ACTIONS
4.1 Immediate
The immediate actions are to make available a good quality vaccine with an acceptable safety and a solid immunity, lasting at least for one year and to undertake epidemiological definition of the infected areas in Africa and Asia.
4.2. Subsequently:
Ensure availability of sufficient amounts of vaccine of acceptable quality.
Review and adapt national legislations and capacity to enforce quarantine, control of animal movements, etc..
Give support to applied research conducted on improvement of vaccine quality, design of a simple and cheap protocol for testing safety and potency, etc..
Coordinate national and regional CBPP control programmes.
5. CONCLUSION
CBPP constitutes a major disease problem which justifies a specific internationally coordinated regional control programme at least for Africa. Progress being accomplished in rinderpest eradication should encourage decision makers to tackle rationally the CBPP problem bearing in mind all differences between the two diseases.
It is proposed that the next EMPRES expert consultation be devoted to the CBPP topic with the objective of addressing control actions to be initiated in different zones according to their current CBPP status.
