Causation and epidemiological features of proliferative lip and facial lesions in Lao goats

Past surveys and studies have identified a syndrome of lip and facial dermatitis as common in Lao goats and identified Orf virus (ORFV) as the likely cause. To more definitively determine the cause of this syndrome, a matched case-control study was implemented in 70 smallholder goat farms and a large-scale goat holding from Savannakhet province, Laos. Forty-one scab samples from goats with lip and facial dermatitis (cases) and 41 paired samples from unaffected animals (controls) were collected from 31 goat holdings over 12 months. Samples were tested using quantitative PCR assays targeting possible pathogens causing such lesions. The prevalence of PCR-positive samples in case and control goats was 100% and 95.1%, respectively, for ORFV (P = 0.15) and 19.5% and 29.3% (P = 0.3) for Dermatophilus congolensis. Pseudocowpox virus and bovine popular stomatitis virus were not detected in any samples. There was a clear difference between the log₁₀ genome copies (GC) per µL DNA extract of ORFV in positive samples from cases (7.00 ± 0.17) and controls (2.62 ± 0.18, P < 0.0001). This was not true for D. congolensis with similar GC detected in the case and control goats. More than 4 log higher GC in affected cases identifies ORFV as the likely cause of the syndrome in Lao goats with little role for D. congolensis. Phylogenetic analysis showed no genetic variation of ORFV in the study samples and close similarity to sequences from China. The findings suggest that orf disease has a sporadic distribution, mostly occurring in goats during the first 6-months of life.