Atypical case of an orf virus infection in sheep

Atypical manifestations with a podal distribution have been occasionally reported in the USA, the UK and Israel in the early 2000s. The lesions were characterised by a tumor-like progression with a lack of remission over months and seemed to affect mostly older lambs and adult sheep, and ultimately led to euthanasia. Here, we report a case from Germany with similar findings, raising the question of whether this presentation may represent a distinct syndrome associated with orf virus infection in adult animals.

In February 2024, an eleven-month-old lamb showed extensive non-resolving proliferative lesions on all four legs around the coronary bands. After euthanasia, pathomorphological and molecular analyses of the affected area were performed. Histologically, the haired skin showed prominent vacuolation and swelling of keratinocytes of the stratum spinosum, reticular degeneration, and extensive epidermal proliferation with eosinophilic cytoplasmic inclusion bodies indicating a poxvirus infection. Transmission electron microscopy and PCR for the B2L and RPA gene confirmed an infection with the orf virus. Phylogenetic analysis revealed that the identified German orf strain was most closely related to an Iranian strain. The strains only differed by one amino acid (A98E) in the B2L open reading frame.

The observed podal tumor-like lesion did not spontaneously resolve and ultimately led to euthanasia of the lamb due to severe lameness. Host and viral factors may play a role in this unusual presentation. The close genetic relationship between the German strain and the Iranian IRFH9 strain is noteworthy but remains elusive. Full- genome sequencing will be required to better understand the evolutionary origins of the viral strain. This appears to be the first report of an atypical manifestation of CE in Germany.