Discussion
Gross pathological lesions observed in the spleen were severe congestion, splenomegaly and severe depletion of lymphocytes. The lesions may be because of leucopoenia and lymphopoenia that were said to be occasioned by apoptosis, necrosis of the lymphocytes or due to activation and mobilization of the lymphocytes to fight the virus (Otesile et al ., 2005; Junt et al ., 2008; Ganowiak, 2012; Liao and Padera, 2013; Jubb et al ., 2016).
Similarly, the lymph nodes were severely enlarged and haemorrhagic likely due to severe haemorrhages and necrosis as reported previously by Jubb et al . (2016). Severe lymphocytes depletion and severe hemosiderosis was recorded in the lymph nodes histologically, which may be due to apoptosis, necrosis or severe erythrolysis (Ganowiak, 2012; Jubb et al ., 2016). Although moderate multifocal white patches on the liver has not been previously reported in ASF, liver in this study showed severe congestion and moderate enlargement with severe necrosis on histopathological evaluation. Previous reports on ASF documented congestion and necrosis as lesions associated with the acute form of the disease and adduced it to marked thrombocytopenia or disruption in blood clotting factors. (Oura , 2005; Otesile et al ., 2005; Jubbet al ., 2016). The kidney of pigs was severely congested with severe cortical petechiae which is a consistent finding previously reported in ASF and severe ecchymotic haemorrhages in the renal medulla which we observed for the first time in ASF. Histopathological examination revealed severe necrosis largely characterized by severe pyknosis and moderate renal tubular protein fat. Similar lesions were also observed in earlier reports on ASF and were attributed to be likely due to severe thrombocytopenia or disruption in blood clotting factors (Oura, 2005; Ganowiak, 2012; Jubb et al ., 2016). The heart on the other hand was observed to have mild focal congestion grossly with severe vascular congestion histomorphologically. The disease was reported by earlier researchers to cause cardiopathology ranging from hydropericardium, hemopericardium and fibrinous pericarditis whichwas said to be associated with the chronic form of the disease. The lesions so recorded in the heart were said to be likely caused by oxidative stress and ischaemia (Oura, 2005; Otesile et al ., 2005; Ganowiak, 2012; Jubb et al ., 2016; Semerjyan et al ., 2018).
The aetiological diagnosis of the disease was by virus culture and indentification via haemadsorption test characterized by erythrocytes attachment to the surface of the infected cells several hours post inoculation. This has been documented to be a reliable and effective method of ASFV isolation (Oura, 2005; Jubb et al ., 2016). Furthermore, the aetiological diagnosis was achieved by amplification of viral glycoprotein VP72 from the tissues of the infected pigs which among others, plays an important role in attaching to and entering target cells. Successful amplification of a 278bp of the glycoprotein by PCR has earlier been reported to be confirmatory of ASFV in a given clinical sample (Otesile et al ., 2005; Fernandez-pinero et al ., 2012; Jubb, 2016; Mwiine et al ., 2019).
Phylogenetic analysis based on the VP72 (b646L) gene sequences showed that the isolate from this study failed to cluster with others downloaded from the Genbank database, including the Nigerian isolates. This observation is inconsistent with earlier finding that Nigerian isolates always cluster together on the tree (Luka et al ., 2017b). The reason for the observed difference is not known for certain, however, it could be an outcome of continued evolution of the virus. It could also be possible that there are unreported strains of the virus circulating in the country, and this, therefore, highlights the need for more extensive studies to characterize the circulating strains of ASFV in the country as previously recommended (Luka et al ., 2017b). This, if done, would serve as baseline for formulating adequate and appropriate control strategies against ASF outbreaks, including vaccine production. Furthermore, the phylogenetic analysis revealed that the virus associated with the disease reported in this study belonged to genotype-I. This further corroborates the previous reorts (Owolodunet al ., 2020; Luka et al ., 2017b) on circulating viruses in Nigeria.
Data availability statement: The data that support the findings of this study as presented in the manuscript are available from the corresponding author, Dr. Tizhe E.V., upon reasonable and/or genuine request.
Ethical statement: Ethical clearance is not applicable in this study as the data were generated from the swine carcasses submitted to the Veterinary Teaching hospital, University of Jos, 2019 for diagnostic purpose.
Acknowledgement: The author’s hereby acknowledge that the PCR and sequencing were sponsored by the ASF research grant of Dr. P.D. Luka and his team to whom the authors remain eternally grateful.
Competing interest: The authors declare that there is no competing interest.