Serological study of pigs for antibody against African swine fever virus in two areas of southern Malawi.

A serological survey was conducted in July 1991 on domestic pigs in two areas of southern Malawi which were severely affected by the African swine fever (ASF) epizootic in 1989-1991. Sixty-six of the 216 owners questioned reported having witnessed ASF in their pigs. Forty-seven owners had pigs with antibodies against ASF virus, and the overall prevalence of pigs with anti-ASF virus antibodies was found to be 12.4%, in 445 pigs sampled in 35 villages. Spread of ASF was thought to occur principally through the slaughter and sale of infected animals, and due to the free-ranging of pigs. Permanent penning of pigs significantly reduced the attack rate (chi 2 = 7.59, P < 0.01, 1df) in pig pens in Thyolo, an area where permanent penning of pigs was widely practised. Feeding of kitchen scraps did not appear to have been an important means of virus spread. Ornithodoros ticks were found in only 1 of the 35 villages. Although virus was not isolated from 203 pooled sera from pigs in the Mulanje district or from collected ticks, the seroconversion of a small proportion of pigs born after the last reported date of ASF occurrence suggests that the virus had continued to circulate to a limited extent in this area.