Molecular Detection and Characterization of Orf Virus in Goats With Clinical Signs From Four Districts of Tanzania

Orf virus (ORFV), a zoonotic member of the genus Parapoxvirus, causes contagious ecthyma in sheep and goats and poses significant economic and public health concerns. Despite frequent outbreaks, molecular data on ORFV circulating in Tanzania remain scarce.

This study aimed to confirm ORFV infection in goats with clinical signs of contagious ecthyma in multiple districts of Tanzania and to characterize the genetic relationships of circulating strains using molecular and phylogenetic analyses.

An outbreak investigation was conducted between May and June 2015 in 11 goat flocks (259 animals) across four districts in Tanzania. Samples including oral swabs, scabs and skin scrapings were collected from clinically affected goats. ORFV infection was confirmed by polymerase chain reaction (PCR) targeting the RNA polymerase gene. Genetic characterization was performed by sequencing the B2L gene, followed by phylogenetic analysis using reference strains from GenBank.

Clinical orf-like lesions were observed in 72 goats, with 24 associated deaths. ORFV was detected in 16 of 22 tested animals, with higher detection rates in scabs and skin scrapings than in oral swabs. Phylogenetic analysis revealed that Tanzanian ORFV isolates clustered within Cluster I and showed high nucleotide similarity (94%-99%) with strains from Africa, Asia and the Americas, including close relatedness to Brazilian and South Korean isolates. Limited genetic divergence was observed among isolates from different districts.

The findings indicate that ORFV is endemic in Tanzania, with closely related viral strains circulating across multiple regions. The observed genetic conservation suggests ongoing transmission among susceptible goat populations. Expanded genomic surveillance and zoonotic investigations are warranted to better understand ORFV epidemiology and public health risks.