Bighorn sheep in Yellowstone battle sore mouth disease

JACKSON HOLE, WYO – As a species, bighorn sheep have had a rough go of it for decades now. Overall numbers continue to dwindle as the sheep have battled through a few population crashes due to pneumonia and other diseases and ailments.

Currently, bighorn sheep in Yellowstone National Park are experiencing yet another nightmare: sore mouth disease. Also known as contagious ecthyma, the illness is thought to be spreading in bighorn rams in Yellowstone. Sore mouth disease is a virus caused by the parapoxvirus. It is transmittable to people if direct contact with infected sheep occurs—a good reminder to never touch wildlife.

Sore mouth disease can cause rams to not want to eat. (NPS)

Sore mouth disease is common in farmed sheep and goats and widespread in wild bighorn sheep in the Rocky Mountains from Alaska to California. It typically spreads 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 that 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.

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