When african swine fever plays at home - Description of an outbreak in Namibia

Introduction - African swine fever (ASF) is regarded as the most serious health threat to the global pig industry and is caused by a complex linear double-stranded DNA virus (ASF virus, ASFV), currently classified as the only member of the family Asfarviridae. Aim - To describe an outbreak of ASF, which occurred in Namibia and was managed during international co-operation therein carried out by the Istituto Zooprofilattico Sperimentale dell'Abruzzo e Molise "G. Caporale" (Teramo, Italy). Materials and methods - The ASF outbreak occurred in the district of Omaruru (Namibia) and affected a small swine herd consisting of about 100 pigs. The herd was part of a hunting farm and was very close to a small abattoir, where warthogs had been recently slaughtered. Clinical signs suddenly onset and affected pigs of different classes of age. Two pigs were necropsied for diagnostic purpose: histopathology, direct immunofluorescence and polymerase chain reaction. Results - At necropsy, all pigs under investigation showed generalized hemorrhagic lesions. Microscopically, recently occurred hemorrhages were mainly observed, along with a severe lymphocytolysis in all lymphoid tissues. Laboratory investigations confirmed the diagnosis of ASF. The outbreak was finally solved by stamping out. Discussion - In Africa, ASFV infection strictly depends upon the "sylvatic cycle", which involves warthogs and ticks of the Ornithodoros moubata complex. The mechanisms of transmission from wildlife and domestic pigs are still unclear, but ticks most likely play a key role. Therefore, the ASF outbreak described herein could represent the prototype of ASF in southern Africa. In that region, ASFV eradication seems not achievable and ASF control should focus on biosecurity measures. As in the present report, acute ASF usually occurs with very high morbidity and mortality, at least in previously unexposed pigs. On the contrary, sub-clinical and chronic infections are more frequent in endemic areas. Pathological findings are extremely useful to diagnose and counteract ASF. A number of hemorrhagic diseases should be considered in differential diagnoses. Anamnestic and epidemiological data prove to be helpful to correctly address the diagnostic process. Conclusions - The recent outbreak in Eastern Europe further confirms that ASF that is a serious transboundary disease, which still negatively impacts the pig industry worldwide. Epidemiological and pathological features described herein are of diagnostic value and of relevance to promptly counteract the spreading and the economic impact of the disease.