Containment or eradication for animal diseases?
Rinderpest has been, perhaps, the most serious of what are termed 'transboundary' diseases, (epizootic diseases which are highly contagious with the potential of rapid spread, irrespective of national borders). There are some fifteen in total which are highly transmissible and variously infect cattle, sheep and goats, pigs, horses or poultry. Since cattle and small ruminants are most important in the agricultural and national economies of most African and Asian countries, six of these diseases have been given priority in efforts to limit their impact and strive for eradication. As well as rinderpest they are: foot-and-mouth disease (FMD); peste des petits ruminants (PPR); contagious bovine pleuropneumonia (CBPP); Rift Valley fever and lumpy skin disease.
EMPRES, an Emergency Prevention System for transboundary diseases world-wide, was established in 1994 to strengthen FAO's role in preventing, anticipating and responding rapidly to outbreaks of those diseases that are not only transboundary but which constrain food security, impede international trade, and in some cases (such as recently with Rift Valley Fever) are a risk to human health. All transboundary diseases are a serious threat but inevitably it has been necessary to focus attention and resources in order to increase the likelihood of achieving success. Rinderpest (cattle plague) was selected as an initial priority because it was the first animal disease for which there was international agreement that it could be eradicated world-wide, in a similar way to the successful eradication of smallpox. Through the Global Rinderpest Eradication Programme (GREP), which co-ordinates eradication campaigns in Africa and Asia, it is hoped that rinderpest will be a disease of the past by the year 2010.
In Africa, rinderpest is now restricted to
relatively small pockets in eastern Africa although an outbreak of
severe rinderpest in wildlife and mild rinderpest in cattle during
1996/7 in Kenya and Tanzania was considered to be the worst for 15
years.
The disease has now been contained but continued surveillance and
monitoring is still required. More recently, samples collected from
within south-eastern Sudan have been confirmed as rinderpest. In view
of livestock movement between southern Sudan and Uganda countries in
the region have been warned by PARC (Pan-African Rinderpest Campaign)
to intensify efforts for both disease surveillance and rapid response
vaccination. NGOs and paravets will have
a vital role to play in this work. In Asia, there is growing
confidence that India and Sri Lanka are now free of rinderpest.
Declarations of provisional freedom have been made for the North-East,
Indo-Gangetic and Island zones of India and it is hoped that further
declarations of provisional freedom will be made this year for the
remaining Peninsular zone of India and Sri Lanka.
CBPP is another disease which causes widespread losses in cattle. Today, CBPP is endemic in much of sub-Saharan Africa and only a few countries, mostly in southern Africa, are reported to be completely free of the disease. Livestock movement is a crucial factor in the transmission of the disease as in Burundi where, because of civil strife, livestock raids and illegal movements of cattle across the border has resulted in the presence of CBPP in two provinces.
Clinical detection of CBPP can be difficult to confirm when the disease is at very low levels. ELISA (Enzyme Linked ImmunoSorbent Assay) kits, which have already proved invaluable in the eradication of rinderpest, are currently being evaluated by the Joint FAO/IAEA Division for the improved diagnosis of CBPP at laboratory level. The assay can be used to test thousands of samples quickly and promises to be valuable not only for initial diagnosis but also for monitoring the effectiveness of control programmes.
Excessive and unseasonal rains in eastern Africa early in 1998 led to an epidemic of Rift Valley Fever (RVF). Although the disease is widely distributed in Africa, infection rates and the spread of the disease was greater than expected with outbreaks reported in cattle, sheep, goats and camels in large areas of eastern Africa (primarily southern Somalia, north-eastern Kenya and northern Tanzania). There is a high risk of future epidemics if there is a recurrence of the abnormal weather conditions experienced recently but some outbreaks of RVF are likely even with a return to more normal weather patterns. Extensive vaccination is not feasible due to the scale of the problem so effective surveillance is advocated in all regions. Two other vector-borne diseases (Nairobi sheep disease and bluetongue) have caused mortality of small ruminants, and others (e.g. lumpy skin disease and bovine ephemeral fever) are also likely to become more prevalent in the next 1-2 years following the excessive rains.
Fewer outbreaks of Foot and Mouth Disease (FMD) were reported in Bolivia, Colombia, Ecuador and Brazil in 1997 compared with recent years. Significant improvement has been achieved in the effectiveness of FMD control programmes across South America where the disease causes severe production losses and trade restrictions.
Over 4 million pigs have either died or were slaughtered in the last year as part of a control program against FMD in the Taiwan Republic of China. It has been established that this new viral strain is highly infectious for pigs but is not transmitted readily to cattle. The 'pig-adapted' virus is giving cause for grave concern in Asia and is already present in Hong Kong, The Philippines, Taiwan and Vietnam. Vaccination is available but, without tighter control measures and more accurate diagnostic systems being established, the virus is expected to invade other countries in the region.
Thousands of pigs are also being affected in West Africa by African Swine Fever (ASF). Contact between free ranging village pigs and wild warthogs in infected zones can maintain ASF infection endemically in many parts of Africa but apparent absence of the tick vector, makes this unlikely in West Africa. The origin of the latest outbreaks is considered to have been infected domestic pigs or their products from neighbouring countries. Emergency control projects under FAO's Technical Cooperation Programme are being implemented for Benin, Cape Verde, Togo and Nigeria, and it is advised that ASF control, eradication and re-stocking should be supported by legislation in the region. Increased public awareness, livestock movement control and involvement of the public sector are also considered important in order to bring ASF under control.
