Abstract

African swine fever (ASF) remains one of the most economically devastating viral diseases affecting domestic pigs globally and continues to pose a major threat to food security in sub-Saharan Africa. ASF is endemic in Nigeria, with recurrent outbreaks attributed primarily to genotype I strains. However, recent reports indicate the emergence and increasing detection of genotype II viruses. This study aimed to characterize ASFV strains circulating in selected states in southwestern Nigeria between December 2019 and March 2021.
In a cross-sectional investigation, spleen tissues (n = 36) were collected from pigs that died during suspected ASF outbreaks across 14 farms. Viral DNA was extracted and amplified by PCR targeting the B646L (p72) gene. Nine representative isolates were further characterized by sequencing partial B646L (p72). The Basic Local Alignment Search Tool (BLAST) was used to find regions of similarity between each of the sequences and phylogenetic analysis was performed using MEGA X.
All samples tested positive for ASFV. Sequence and phylogenetic analyses identified all characterized isolates as genotype II. The isolates clustered closely with genotype II strains previously reported in Africa and Europe, including strains from Tanzania, Madagascar, Mauritius, and Italy. The deduced amino acid substitutions at positions 376 (I→V) and 383 (P→A) in the p72 gene were consistent with established genotype II signatures. All sequences were deposited in GenBank (accession numbers ON946174–ON946182).
These findings confirm the circulation of ASFV genotype II in southwestern Nigeria and suggest sustained widespread presence in the sampled population. Continuous molecular surveillance, strengthened farm biosecurity, and coordinated regional control strategies are urgently required to mitigate the impact of ASF on the swine industry in Nigeria.

Key words: African swine fever, transboundary disease, viral genotype, pig disease