Identification of ORF Virus in an Outbreak: A Molecular and Pathological Perspective

Orf virus causes infections in sheep and goats with lesions especially around muzzle and mouth. The disease is widespread, and most sheep-rearing countries are not free of infection. Disease is caused by ORF virus (ORFV) which belong to Poxviridae under genus Parapoxvirus. Infection has a mild course and lesions start improving within a week. Most affected individuals are the lambs and kids under 2 months of age. The disease primarily affects mammary tissues and is transmitted to suckling lambs. In this study presence of ORFV in a sheep flock was investigated using molecular and pathological techniques. Flock had 508 sheep of which was 102 lambs. Ten of the 102 lambs were affected by the disease showing pustular lesion in mouth region of which 5 died. Tissue samples were collected from mouth lesions of 10 symptomatic lambs. For pathological analysis tissues were routinely processed, and stained. After microscopic examination, epidermal thickening and hyperkeratosis were noted. Additionally, finger-like structures extending from the epidermis to the dermis (rete ridges) were apparent. Same tissue samples were homogenized; nucleic acid was isolated and were tested for ORFV nucleic acid with PCR primers specific to B2L region. All 10 samples were positive for the presence of ORFV, confirming the ORF infection. Mortality rate of disease in lambs was decided to be 4.9% (5 of 102 lambs). This study reports the first molecular characterization report from our province for the first time. Furthermore, considering the lack of human infection, zoonotic potential of the field isolates is thought to be low.