Genetic characterization and diversity of porcine circovirus type 2 in non-vaccinated South African swine herds.

Abstract

The porcine circovirus type 2 (PCV2) is a swine infectious viral pathogen of great significance in global swine herds. It was recently detected at another Province of South Africa sequel to the first detection of North American-like strain (PCV2a) at Gauteng about two decades ago, but there is a dearth of information about the genomic features and diversity of the viral strains in circulation within the country and the entire sub-Saharan Africa region. To date, only one complete genome of the virus from South Africa is available on global data base. This current effort is therefore geared towards the full-genome characterization of the circulating PCV2 strains in the pigs of Eastern Cape Province. With the use of conventional polymerase chain reaction method, fifteen complete PCV2 genomes were successfully amplified, sequenced and assembled from field samples obtained from non-vaccinated pigs in the region. Neighbor Joining and Maximum Likelihood phylogenetic analyses of the ORF2 gene and full genomes unanimously showed that most of the assembled genomes (11) belong to genotype PCV2b. Furthermore, three of the characterized sequences formed clade with other reference mutant PCV2b and PCV2b subtype 1C (i.e. PCV2d) strains from the USA, China and South Korea. The last sequence, however, clustered with other reference strains belonging to PCV2 intermediate clade 2 (PCV2-IM2), recently identified in a global PCV2 strains phylogenetic analysis. This study reports the first complete genome sequences of PCV2b, PCV2d and PCV2-IM2 in pigs from South Africa, and it gives a possible insight into the genetic characteristics and variability of the viral strains presently in circulation within the country. It further emphasizes the need for more stringent measures in curtailing the introduction and spread of transboundary swine pathogens in the country and entire Southern African region.