Research points a finger towards a bacterium that may be the primary challenge to rebuilding bighorn populations in the West, reports the Wildlife Management Institute. According to a report released in July, Washington State University (WSU) biologists isolated Mycoplasma ovipneumoniae in tissue taken from dying lambs in Hells Canyon, which borders Oregon, Washington and Idaho. It is believed the bacterium increases a sheep's chances of dying from pneumonia?the leading cause of bighorn mortality?by reducing the lung's capacity to fight off the disease.

"This is the first problem I've worked on where there is quite a bit of evidence piling up where the agent is a mycoplasma," said Tom Besser, a professor in WSU's Department of Veterinary Microbiology and Pathology.

Thousands of sheep have died from pneumonia in the last 50 years, making reintroduction and population-stabilization efforts more difficult. In herds infected with Mycoplasma, more than half the animals succumbed to pneumonia, with lambs being most susceptible to infection.

The connection of Mycoplasma to pneumonia in bighorns is not new. A 1970 study by biologists at the Pennsylvania State University Department of Veterinary Science showed a high incidence of Mycoplasma spp. in a pneumonia complex of captive bighorns.

At least until now, biologists in other states believe that other agents, including Pasteurella bacteria, have been the primary cause of bighorn pneumonia.

Mycoplasma infections are not uncommon in domestic sheep, which are the likely source of transmission to wild bighorns, but domestic sheep are more likely than bighorns to survive infection. In addition, it does not appear that bighorns are able to build resistance to the disease over generations. When considered with the lack of success developing vaccines for domestic sheep and coupled with the difficulty in vaccinating large, dispersed populations of bighorns, finding a source for the deadly infections is only the first, but hopefully big step in solving the bighorn mortality problem.