SUMMARYA serological survey of free-ranging domestic pigs in the Central and Southern Regions of Malawi, together with laboratory data on confirmed cases of African swine fever (ASF) and data from interviews with pig owners, undertaken over a four-year period from 1981-4, has enabled the ASF enzootic area of Malawi to be identified. The area covers much of the western part of the Central Region and includes Mchinji district and parts of Kasungu, Ntchisi, Dowa and Lilongwe districts. Mortality is substantially less than 100 % in outbreaks within the enzootic area but approaches 100 % in outbreaks outside this area, as shown by both the serological investigation and the interview data.

SUMMARYTicks of the Ornithodoros moubata complex were collected from domestic pig sties and dwelling houses, and from a warthog habitat, and tested for the presence of African swine fever (ASF) virus. Collections were made in 9 of the 24 districts of Malawi, these being primarily the districts in which 0. mowbata is most numerous. ASF virus was isolated from ticks collected in both domestic pig sties and houses in certain villages in Mchinji district where ASF outbreaks had recently occurred. Mchinji district is in the centre of a large ASF enzootic area which stretches into other districts of Malawi and -.also into Zambia and Mozambique. The high titre of virus in some of the ticks demonstrates that 0. moubata can act as a virus reservoir and potential vector of disease in the field situation in Malawi.

SUMMARYCases of African swine fever (ASF) confirmed in the laboratory in 1985 and 1986 and other data obtained since 1984, in particular an extension of the serological survey of free-ranging domestic pigs undertaken from 1981 to 1984, are presented to give an updated survey of the ASF situation in Malawi and a revised estimate of the ASF enzootic area. Evidence is presented that the area may include some border areas in Dedza and Ntcheu districts and may be expanding in some localities.

SUMMARYA detailed study was made in 1983-5 in three villages in Mchinji district in the African swine fever (ASE) enzootic area of Malawi, following an outbreak of ASF which affected all three villages.Ticks of the Ornithodoros moubata complex were collected from both pig sties and houses shortly after the outbreak. and approximately 240/ contained ASF virus. The proportion of ticks infected did not differ significantly in the three villages, or more surprisingly in different types of premises, and was equivalent in all stages of ticks. The proportion infected decreased with the passage of titne but infected ticks were still present in all three villages 8 months after the outbreak, some with high titres of virus.The proportion of seropositive pigs in the three villages approached t 00( following the outbreak, with many apparently healthy pigs beiing seropositive. It is suggested that Malawian isolates of ASF virus mav be less virutlent in African than European breeds of (lomestic pig. 1981(Haresnape, 1984 Haresnape, Lungu & Mamu, 1985;Haresnape, Lungu & Mamu, 1987). One of these was in Bongera locality in 1983 where at least 130 pigs died, but estimates of the numbers of pigs affected have always been difficult to obtain. Since many more outbreaks probably go unreported, it is likely that several thousand village pigs have died as a result of ASF in the enzootic area of Malawi over the last few years, and many more in epizootics outside the enzootic area which are characterized by a mortality approaching 100% (Haresnape, Lungu & Mamu, 1985). INTRODIU(TIONA serological survey undertaken between 1981 and 1984 included 10 localities in Mchinji district, and seropositive pigs were identified in all of them. Between 21 and 74 % of the pigs were seropositive and highest proportion was in the southwest part of the district. Mortality was estimated from serological data to be between 47 and 83 % for one locality in the district and between 77 and 92 % for another (Haresnape, Lungu & Mamu, 1985).It has been suggested that most outbreaks of ASF outside the enzootic area probably start following introduction of infected meat from an affected area, but that some outbreaks within the enzootic area may represent new incursions of virus from a natural reservoir (Haresnape, Lungu & Mamu, 1985). The soft tick, Ornithodoros moubata, which is known to be a reservoir of ASF virus and vector of the disease (Plowright, Parker & Pierce, 1969; Thomson et al. 1983), is common both in houses and pig pens (kholas) in the enzootic area, particularly in Mchinji district (Haresnape & Mamu, 1986). Collections of these ticks were started in 1982, and examined for the presence of ASF virus. Up to November 1983, 1262 ticks collected from pig kholas in eight villages in Mchinji district were tested, and only three were infected. None of the 977 ticks collected from houses in the same villages were infected. The three infected ticks were from kholas in three different villages in the west part of Mchinji district and there had been suspected ca...

SUMMARYThe distribution of ticks of the Ornithodoros moubata complex in different habitats in Malawi, particularly pigsties and houses, was established from a four-phase survey undertaken between 1982 and 1985. The first phase consisted of preliminary interviews, the second phase consisted of a questionnaire to Veterinary Assistants (VAs) in rural areas, the third involved tick collections by VAs and the fourth involved both interviews and tick collections by members of the Central Veterinary Laboratory, Lilongwe. The area in which 0. moubata is found in pigsties includes much of the African swine fever (ASF) enzootic area, and it seems likely that the enzootic area could become larger in future. The occurrence of 0. moubata in warthog habitats was also investigated.