Collaboration for combating CBPP
Extensive international and national efforts are currently being directed towards Contagious bovine pleuropneumonia (CBPP) - a
transboundary disease which is, at the present time, a major cattle plague in Africa and therefore a serious obstacle to livestock development in the
region. Control has previously been achieved in many sub-Saharan countries during this century only to return at a later date. Today, CBPP is present
in much of sub-Saharan Africa and only a few countries are reported to be completely free of the disease. Substantial support from DFID (email
nr-policy@dfid.gov.uk), the Department for International Development, has been provided to allow
collaborating institutions in the UK and Africa to focus research on vaccine development and molecular
epidemiological studies to help combat the disease.
| Threat of CBPP |
|---|
| Seasonal cattle movements by pastoralists resulted in the spread of the disease in 1990 from Kenya, where the disease has been
endemic for some time, into the Ngorogoro crater in Tanzania, which had been free of CBPP for 30 years. As a result of drought, failure to report
outbreaks of the disease and continued, unrestricted movement of livestock, CBPP spread further south in 1995 causing over 14,000 cattle deaths in
just six months. Most of Central and Eastern Africa, from Uganda down to Zambia, now have cattle infected with CBPP. In Botswana, the disease re-emerged in early 1995 after an absence of 50 years. Border controls which were relaxed after the end of the Namibian War of Independence allowed the uncontrolled movement and smuggling of livestock, resulting in the outbreak of CBPP. Despite rapid control efforts, including restriction of cattle movement, the erection of fences & the slaughter of infected herds, the disease continued to spread and, in 1996, 300,000 cattle in the infected region had to be slaughtered. This proved effective and, in January 1997, Botswana was declared 'provisionally free' from CBPP. However, Zambia, and therefore the SADC (Southern African Development Community) region, is currently facing an emergency posed by the uncontrolled presence of CBPP in eastern Angola. FAO EMPRES reports that the situation is now so acute that it demands international attention to avert disastrous losses in livestock and escalating control expense in the future. |
CBPP is a disease of the lungs caused by a bacterium (Mycoplasma mycoides var. mycoides). Symptoms include fever, loss of appetite and a severe cough and, if left unchecked, outbreaks can result in mortality rates of over 50%. However, many cattle show no signs of disease despite being infected and others recover quickly after suffering from a transient mild form of the disease, yet these animals can carry the infection for up to two years and may be responsible for passing on infection at a later date. Because of the nature of this disease, vigilance and recognition of CBPP are essential if effective control and elimination are to be achieved before large numbers of cattle are lost through infection or because infected herds have to be slaughtered. (see box)
Vaccination of cattle is possible and two freeze-dried vaccines (T1SR & T144) are currently being used for immunizing against CBPP. However, cattle suffer side effects as the vaccination causes mild infection and, if given as a tail tip injection, causes the tail to become inflamed and, in 40% of cases, drop off. Both vaccines also only provide protection for a year. Farmers are therefore often reluctant to have their cattle immunized against CBPP and prefer to treat their cattle with antibiotics. In addition, T1SR has failed to control recent outbreaks and vaccine efficacy trials for both vaccines in Kenya and Côte d'Ivoire have indicated that levels of protection achieved were not as high as expected with only 50% of cattle developing immunity against CBPP. DFID funds are to be made available for checking batches of vaccines currently being produced to ensure that the original seed stock of the vaccine has not been overgrown leading to a reduction in immunogenicity which may explain the poor levels of protection observed in the field. This checking also ensures that the vaccines have not become contaminated. Further studies are also required to check the immunizing dose and the route of administration of the vaccine.
Development of a new vaccine which would cause fewer post-vaccinal reactions and be able to confer immunity that lasts longer than a year is also being supported by DFID. This vaccine being developed is known as a capsular polysaccharide-conjugate vaccine and will be similar to the Hib vaccine currently used to vaccinate children against Haemophilus influenzae type b (Hib) which can cause bacterial meningitis and pneumonia.
Recent technological developments, which are also helping in the fight against CBPP, are DNA insertion sequences that allow DNA fingerprinting of the causal strains of CBPP. This enables vaccine stocks to be checked for contamination and provides an effective epidemiological tool to map the spread of disease.
Future control of CBPP will require successful implementation of these molecular and vaccine technologies on a continental scale in addition to the work that is currently being conducted on a national basis. Therefore active collaboration of national veterinary services will be essential and dissemination of information and training will play an important role in the effective use of these tools.
