Sore mouth disease suspected in Yellowstone bighorn sheep

MAMMOTH HOT SPRINGS, WY – Sore mouth disease (also known as contagious ecthyma) is thought to be responsible for an illness observed among bighorn rams in Yellowstone National Park. Sore mouth disease is a virus caused by the parapoxvirus. It is transmittable to people if direct contact with infected sheep occurs. The park reminds people to not approach or touch wildlife.

Sore mouth disease is common in farmed sheep and goats and widespread in wild bighorn sheep in the Rocky Mountains from Alaska to California. Typically spread from ewes to lambs, the disease can manifest itself as scabby sores around the mouth and face. Lesions disappear in 2-4 weeks and animals typically heal without scarring. Generally, affected animals recover but deaths can occur in severe outbreaks, especially with young animals who cannot feed. The virus has the greatest effect on lambs that refuse to nurse because of sore mouths.

So far, only breeding age rams in the park have been observed with lesions. This is likely a result of frequent contact with each other and possibly infected ewes during the breeding season. The disease is difficult to control in bighorn sheep. In most situations, control efforts are not warranted since the disease is typically self-limiting as animals build up protective antibodies.

Park biologists will continue to monitor the infected animals.