Comparative and retrospective molecular analysis of Parapoxvirus (PPV) isolates

Species members of the genus Parapoxvirus (PPV) within the family Poxviridae cause contagious pustular dermatitis in small ruminants (Orf virus, ORFV) and mostly mild localized inflammation in cattle (bovine papular stomatitis virus, BPSV and pseudocowpox virus, PCPV). All PPVs are known to be zoonotic, leading to circumscribed skin lesions in humans, historically known as milker's nodules. Human PPV isolates are often ill defined concerning their allocation to an animal origin. Here we present a comparative molecular analysis of a unique collection of 21 historic and recent human and animal PPV cell culture isolates (and two PPV DNA samples). Cell culture PPV propagation was restricted to primary ruminant fibroblasts and was strictly kept at low passages to avoid genomic changes by in vitro influences. For molecular arrangement of the isolate DNAs and their attribution to established PPV species DNA fragments of the PPVs were generated by two different discriminating PCR protocols, targeting the major part of the open reading frame (ORF) 011 (B2L gene) and the complete ORF 032. Multiple sequence alignments and phylogenetic analysis of both genes resulted in affiliation to the known PPV species. The sequences from the ORF 032 allowed discrimination of the isolate DNAs at a higher resolution. Human PPV isolates could be clearly assigned to the PPV species belonging to the reported or assumed animal host of transmission. For the first time, a whole PPV genome sequence comparison of a human biopsy derived virus (B029) and its ovine counterpart (B015) originating from a defined Orf outbreak in Germany is provided, revealing their well conserved relationship. Thus human PPVs can be molecularly retraced to the PPV species indicating the animal of transmission. After transmission to the human host, molecular conservation of the animal's virus peculiarities indicative for a PPV species became evident.