Contagious ecthyma or the orf virus

Orf is a contagious virus of sheep and goats that can be transmitted to humans, says Prof Cheryl McCrindle.

Contagious ecthyma or the orf virus
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Orf occurs mainly in sheep and goats, and is caused by a parapoxvirus. In lambs and kids, growths and swellings develop on the skin around the lips and nostrils. In adult sheep and goats, growths can occur on the lips, muzzle, face, ears, teats, vulva and prepuce of male goats. Outbreaks can infect almost 100% of the flock and up to 10% can die, with unweaned lambs and kids especially vulnerable. Orf can be mistaken for foot-and-mouth disease, blue tongue, photosensitisation or ulcerative dermatosis.

Transmission
In South Africa orf tends to occur seasonally during warm, wet weather. Outbreaks often occur during the lambing season.
In goats, orf may be caused by browsing green shoots on thorny shrubs, such as Acacia. The thorns cause small punctures on the lips, and the virus can enter and multiply in the wounds. The thorns can be a source of infection for other goats. Scabs on an infected goat or sheep can harbour the virus for many months and may be the reason for outbreaks in a subsequent season.

Economic effects
Young lambs and kids are more susceptible than adults that have probably had the infection previously. Affected lambs and kids unable to suckle due to painful lesions on the lips and nostrils can die of thirst and hunger. Painful lesions on the teats of the goat or ewe will cause mothers to reject suckling young. Sub-acute or chronic mastitis has been shown in milk goats experimentally infected with the orf virus.

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Although it’s not known if milk from an infected animal could infect humans, or suckling young, it should be discarded. This impacts on the profit of goat milk producers. Flock fertility can be affected by lesions on the prepuce or vulva during the breeding season, making mating extremely painful. An orf outbreak can lead to production losses, as fewer kids or lambs are born and survive to weaning.

Vaccination
A vaccine can be used to increase the flock’s general immunity. However, an outbreak only lasts about two to three weeks and you can lessen the chances of fatalities by hand-feeding affected lambs and kids. Gentian violet can be painted onto scabs. Be careful not to become infected when handling sick sheep and goats, as orf can cause painful lesions on the hands and face.

In people with compromised immune systems, a severe form of viral outbreak has been described, with large cabbage-like growths, and a medical practitioner must be consulted. Infected humans can also re-infect sheep and goats.

Vet Prof Cheryl McCrindle has an interest in assisting small-scale and emerging farmers with animal health and production. She was recognised in 2006 as Shoprite Checkers Woman of the Year in Education for her courses in primary animal health care. Contact her at [email protected] with ‘Animal health’ in the subject line.