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Virus blamed for sore mouth disease in Yellowstone bighorns

Yellowstone National Park biologists believe a contagious ecthyma called “sore mouth disease” is responsible for an illness found in bighorn rams in the park. The disease is a virus caused by the parapoxvirus.

The disease is transmittable to people if they have direct contact with infected sheep.

The disease is common among farmed sheep and goats and widespread in wild bighorn sheep in the Rocky Mountains. It is typically spread from ewes to lambs. It can manifest itself as scabby sores around the mouth and face.

The lesions disappear in 2 to 4 weeks and the animals typically heal without scarring.

Although deaths can occur in severe outbreaks, especially young animals that cannot feed, affected animals usually recover. The virus has the greatest effect on lambs that refuse to nurse because of sore mouths.

So far, only breeding age rams have been observed with lesions in the park. Officials said that is likely a result of frequent contact with each other and possibly with infected ewes during the breeding season.

Park biologists said the disease is difficult to control in bighorn sheep. In most situations, they say the disease is self-limiting as animals build up protective antibodies.

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