Intra-genotypic resolution of African swine fever viruses from an East African domestic pig cycle: a combined p72-CVR approach.

Two of the 22 presently recognised African swine fever (ASF) virus p72 genotypes are genetically homogeneous and are associated with domestic pig cycles. Of these, genotype VIII comprises just two p72 variants, designated 'a' and 'b' in this study, and is confined to four East African countries where it has caused numerous outbreaks between 1961 and 2001. In order to resolve relationships within this homogeneous genotype, the central variable region (CVR) of the 9RL open reading frame of 38 viruses was characterised and the resulting dataset complemented with seven published sequences. Phylogenetic analysis of the 45 taxa resulted in seven discrete amino acid CVR lineages (A-G). CVR lineage F, 84 amino acids in length and spanning a 40-year period, comprised 26 isolates from Malawi, Mozambique, Zambia and Zimbabwe. The second largest lineage (E), consisted of 10 viruses causing outbreaks over a 10-year period in Zambia, Malawi and Mozambique whilst the remaining five lineages were country-specific and represented by four or less viruses with a maximum circulation period of three years. A combined p72-CVR analysis resulted in eight discrete lineages corresponding to eight unique p72-CVR combinations. One of these, b-F, appears to have arisen by convergent evolution or through an intra-genotypic recombination event, as the individual p72 and CVR gene phylogenies are incongruent. This raises the possibility of intra-genotypic recombination in ASF viruses for the first time. However, given the repetitive nature of the CVR region, convergent evolution cannot be excluded and may be the more likely explanation.