Orf lesions on the mouth of sheep are caused by which type of virus?

• A. Parapoxvirus
• B. Adenovirus
• C. Papillomavirus
• D. Poxvirus

Answer: (A)

Orf lesions in sheep are caused by a virus in the genus Parapoxvirus. Parapoxviruses are a group within the Poxviridae family that specifically produce contagious external lesions around the lips and mouth of small ruminants. This makes parapoxvirus the best label for orf, because it’s a distinct genus associated with contagious ecthyma in sheep and goats. Other listed viruses cause different diseases—for example, adenovirus tends to affect respiratory or ocular tissues, and papillomavirus causes warts—so they don’t fit the problem as precisely as parapoxvirus does.