106 the Epidemiology and Control of Foot
Total Page：16
File Type：pdf, Size：1020Kb
106 THE EPIDEMIOLOGY AND CONTROL OF FOOT-AND-MOUTH DISEASE IN THE ASEAN REGION P.G. Joseph, Veterinary Research Institute, Ipoh, Malaysia. SUMMARY The earliest record of foot-and-mouth disease (FMD) in the ASEAN region was in Indonesia in 1887. Brunei had never recorded the disease while the only records in Singapore were in 1935 and 1973. In Malaysia, the disease was recorded only in the Peninsula; East Malaysia was never affected. In Indonesia the disease is now confined to Java. It is endemic in the Philippines and Thailand. The disease is commonly observed in cattle, buffaloes and pigs and rarely in goats and sheep. In calves and in pigs it can be severe, in most others it is mild. In Thailand and the Philippines, both epidemic and endemic patterns of the disease occur. The 1978/79, 1980/81 and 1985 outbreaks in Malaysia and the 1983 outbreak in Indonesia were more recent epidemics. The most important means of spread is with the movement of infected animals. The predominant virus type in the ASEAN countries is type 0. Indonesia has recorded only type 0, Malaysia type A in 1973, type 0 from 1978 to 1984 and Asia 1 in 1985. In the Philippines type 0, A and C have been recorded whereas in Thailand types 0, A and Asia 1 are present. The factors that influence control measures are many and include geographical features, animal movements between and within countries, epidemiological surveillance, diagnostic capabilities, vaccine supply, funding and public co-operation. The current control measures in Brunei, Singapore and East Malaysia are aimed at maintaining their free-status. Indonesia and Malaysia are working towards eradication of the disease. In Thailand and in the Philippines the strategy is to create disease-free zones as the first step in the eradication of the disease. INTRODUCTION Foot-and-mouth disease is a highly contagious, acute viral disease of cloven-footed animals. The disease is characterised by a high fever (upto 1070F), formation of vesicles and erosions in the mouth, tongue, muzzle, teat and feet, salivation and lameness. The disease has an incubation period of 1 to 5 days or longer and in a susceptible population results in almost 100% morbidity. Mortality in the young is around 50% whereas in the adults it is about 5%. The disease is transmitted through direct contact, aerosal spread, infected animal by-products and fomites. The foot-and-mouth disease virus was first isolated in 1897. It is classified with the aphthovirus as a member of the picornaviridae. There are seven immunologically and serologically distinct types of virus identified as types 0, A, C, SAT-1, SAT-2, SAT-3 and Asia 1. Within the seven types are at least 61 sub-types. The SAT virus types have never been recorded east of Iran. The distribution of the disease is worldwide except for Australia, Japan, New Zealand, islands of the Western Pacific, North and Central America and parts of Western Europe. The earliest recognition of the disease in the ASEAN region was in East Java in 1887. In the Philippines the disease has been endemic since 1902 or probably earlier. In Malaysia and Singapore the disease was reported in the early thirties but for 34 years (1939 to 1973) and 38 years (1935 to 1973) Malaysia and Singapore respectively were free of the disease. The first official record of the disease in Thailand was made in 1953 and it has been endemic since then. Brunei and the east Malaysia states of Sabah and Sarawak have never recorded the disease. Currently the disease is endemic in Thailand and in parts of the Philippines, Indonesia and Peninsular Malaysia (FAO/APHCA Report, 1984). EPIDEMIOLOGICAL FEATURES Species affected: In all outbreaks of the disease cattle and buffaloes were affected. However, in the 1977 and 1980 outbreaks in Central Thailand and in the 1978/79 and 1980/81 outbreaks in Peninsular Malaysia, Proceedings of the 4th International Symposium on Veterinary Epidemiology and Economics, 1985 Available at www.sciquest.org.nz 107 a large number of pigs were affected as well. Similarly in the Philippines the outbreaks in 1975, 1976 and 1980 involved a large number of pigs and currently most outbreaks in the Central and South Luzon are in pigs (Mago, 1984). Reported cases in sheep and goats are rare and these animals are not thought to play a significant role in the epidemiology of the disease. Potential wildlife include several species of deer, wild cattle (banteng) and pigs. The role of these in the epidemiology of the disease is unknown. Virus types: Virus types A, 0, C and Asia 1 have been recorded in the ASEAN region as shown in the table below. Table 1: FMD virus types and sub-types in ASEAN Country Virus types and sub-types Thailand 01; 0 (Bangkok, 80); A15 ; A22 -like (Songkla, 73); Asia 1 Malaysia A -like (73); 0 (78-84); Asia 1 (85) 22 1 Singapore -like (73) A2 2 Indonesia 0 (Bali, 62); 0 (Java, 83) 11 1 Philippines 0 • A • C 3(75-79; 84) l 24 3 Disease pattern: Both the epidemic and endemic patterns of the disease may occur in a country as was seen in Thailand, the Philippines and Malaysia. The epidemics have occurred at irregular intervals and are usually widespread involving a large number of animals. Several inter-related factors are probably responsible for such epidemics e.g. emergence of more invasive virus strains, emergence or importation of new antigenic sub-types, waning immunity, large scale movement of infected or carrier animals, and weather patterns particularly conducive to spread of infection. The endemic disease is characterised by the occurrence of a number of small localised outbreaks in which virus spread is often comparatively slow and self-limiting. Endemic FMD also exhibits a seasonal pattern, with the highest incidence during the wet season and during major festivals. Disease transmission: The most important source of virus spread in the region is with the movement of infected animals. Airborne virus spread is less important, close contact between animals is required for efficient virus transmission. Mechanical transmission is less likely to occur in tropical climates because of poorer virus survival in hot weather. In pigs, swill feeding is another means of virus spread. In the Philippines, importation of meat from South America, was thought to be responsible for the introduction of A24 and C3 virus sub-types. Although Malaysia imports beef from FMD infected India, it restricts import to deboned beef without lymph nodes and organ meat. Although transmission from carrier animals has never been proven it has been suspected as the cause of outbreaks. In Java, Indonesia, carrier animals have been suggested as the source of the July 1983 outbreak (Sukobagyo and Teken Temadja, 1984). CURRENT CONTROL MEASURES Brunei, Singapore and the East Malaysian States of Sabah and Sarawak continue to maintain their free status by enforcing the ban on the importation of animals and their products from FMD, affected countries Proceedings of the 4th International Symposium on Veterinary Epidemiology and Economics, 1985 Available at www.sciquest.org.nz 108 or areas. The island status of these regions coupled with a low livestock population are factors in their favour. These countries would attempt to stamp out the disease if it ever occurs in their territories. Singapore has made contigency plans to use vaccines should a "stamping out" policy be difficult to implement. In the Philippines the major islands of Penay, Cebu, Samar, Leyte and Palawan have been free of FMD for more than eight years. The disease is, however, endemic in the islands of Luzon (particularly in the Metro-Manila area in Central Luzon), Masbate and Mindano (particularly in South Cotabato). In March 1982, a small outbreak took place in the island of Negros. Mindoro, where the previous recorded case was in 1965, was affected in June 1984 (FAO-WHO-OIE Animal Health Yearbook 1984). The National FMD Control and Eradication Programme is still in its first phase. In this phase the incidence of the disease is being reduced by vaccination, quarantine and movement restrictions. A trivalent imported vaccine (0, A, C) is being employed but vaccination coverage is in the order of 10-20% of susceptible population. Vaccination is provided free to smallholders and charged for commercial farmers. In Indonesia, the occurrence in Java of FMD in July 1983 put back the eradication programme. For the three years from 1980 to 1982, no case of FMD was reported in the country and Indonesia was on the verge of declaring itself free of the disease. Mass vaccination of all cattle and buffaloes in Java began immediately and by December 1983 the outbreak was effectively controlled with no case being reported since then. In the first phase of the vaccination campaign (1983/84) vaccination was carried out twice at an interval of 2-4 weeks. In the second phase (1984/86) only one vaccination is to be given annually. Total vaccination coverage for a population of over 4.5 million cattle and buffaloes in Java was over 95% in the first phase (FAO-WHO-OIE Animal Health Yearbook, 1984). Both locally produced and imported vaccines are used, and provided free of charge. In Peninsular Malaysia, the 1973, A22-like outbreak was eradicated by a "stamping out" method. The 1978/79 and 1980/81 01 outbreaks were effectively controlled by area-wise vaccination which ultimately extended to the whole country (Joseph, 1981). There were two isolated outbreaks due to 01 virus in December 1982 and May 1984 (Joseph, 1984). In June 1985, however, an outbreak due to Asia 1 took place in Kelantan State which later extended to the adjacent Trengganu State.