African swine fever

African swine fever (ASF), a highly contagious viral disease of swine and other porcine animals (generally confined to the African continent, part of Western Europe and Cuba), is caused by African swine fever virus of genus Asfivirus under family Asfarviridae, an enveloped DNA virus. Several genetically distinct groups of ASF virus have been identified by RE analysis of the genome. African swine fever virus infects domestic and wild pigs, warthogs, giant forest hogs and bush pigs. The disease is not reported in India.

Epidemiology: In sylvatic cycle, virus is maintained asymptomatically in wild pigs and soft ticks of the genus Ornithodoros transmit the virus as biological vectors. Trans- stadial transmission in different developmental stages of ticks takes place.In domestic cycle, ASFV is transmitted by the bite of infected ticks or through infected meat to domestic pigs. From infected pigs, disease spreads rapidly by contact and aerosols.

Clinical signs: Only domestic and wild boars express clinical disease whereas African wild pigs do not. The clinical signs include high fever, leucopenia, listlessness, incoordination of gait and cyanosis. Vomition, diarrhoea and lachrymal discharges may also be observed. Haemorrages form the nose and anus. Pregnant sows often abort. Death takes place from 4 to 7 days after the onset of fever. The mortality may approach 100% in severe epidemics. Although the symptoms and lesions are similar to classical swine fever but severe lesions of lungs, gall-bladder and excessive body fluids are common in African swine fever.

Diagnosis: The ASF virus replicates in swine bone marrow or leukocyte cultures with cytolysis. Haemadsorption of infected cell culture (PK15 and Vero) can be demonstrated. Laboratory test like FAT, CFT and AGID are required to differentiate from classical swine fever virus.

Prevention and control: The disease is controlled by strict quarantine and slaughter  in the absence of a suitable vaccine. Smedi A group of porcine enteroviruses of serotypes 2 to 11 are associated with still birth,mummification, embryonic death or infertility in sows and hence the acronym. Similarly, porcine parvovirus is also associated with such conditions. These conditions are responsible for embryonal mortality and infertility and therefore, are of economic significance to swine industry.