Detection of African swine fever virus in archived Formalin fixed Paraffin embedded swine tissue sections in Uganda using Immunohistochemistry (IHC) and Polymerase chain reaction (PCR)

Abstract Background African swine fever (ASF), a devastating viral disease of pigs, is one of the main hindrance to pig farming in sub-Saharan African. Sporadic outbreaks of the disease occur annually in various regions of Uganda most of which remain undocumented. This study employed histopathology, immunohistochemistry and conventional PCR comparatively on 290 formalin fixed paraffin embedded swine tissues in diagnosis of ASF. ASF was confirmed by conventional PCR using diagnostic primers recommended by World Organization for Animal Health, (forward primer, 5’- TGGATACCGAGGGAATAGC- 3’) and (reverse primer, 5’-CTTACCGATGAAATGATAC- 3’). Results It was found out that, more than a third of the archived pig lymphoid tissues, (lymph nodes 33.3%, 95/285 and spleen; 42.8%, 120/280) had lesions suggestive of ASF. In average, 17% and 15% of the archived samples had ASF viral DNA and antigen respectively. The positivity rate for ASF in the tested tissue samples was higher in spleen (PCR, 17.5% and IHC, 16.1%) than in other tissues. More than half (51.1%, 48/94) of the lymph nodes and 41.9% ( 49/117) of spleen tissues that had lesions suggestive of ASF tested positive for ASF using conventional PCR. Conclusion ASF is still wide spread in Uganda and is one of the major threats to pig production in the country. Immunohistochemistry other than PCR, is an effective and reliable technique for diagnosing ASF in tissues even after a long period of archiving.