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.