Organism ID'd that may be killing sheep

updated 8:16 a.m. ET July 3, 2007

BOISE, Idaho - An organism that may have played a part in killing thousands of bighorn sheep in the West over the last five decades and in thwarting repopulation efforts has been isolated in a lab and found in struggling bighorn herds in the wild, biologists say.

Research done at Washington State University on tissue taken from dying lambs captured in Hells Canyon — a chasm that borders Idaho, Oregon and Washington — isolated a type of bacteria called mycoplasma ovipneumoniae.

Biologists say that could be the initial organism that attacks the sheep and works by inhibiting the ability of hair-like structures in airways to eliminate bacteria that lead to deadly pneumonia.

Biologists have known that pneumonia often proves fatal to the wild sheep, but have been stumped for years as why so many bighorns are susceptible.

"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. He works at the Washington Animal Disease Diagnostic Laboratory on the school's Pullman, Wash., campus.

In herds known to be infected with mycoplasma, anywhere from half to all the lambs die each year from pneumonia. The lambs are most susceptible mainly because their immune systems are not fully developed, said Frances Cassirer, a wildlife research biologist with Idaho Fish and Game.

Among adult bighorns that hadn't previously been exposed to mycoplasma, 25 percent to 75 percent die, she said, noting the variation could be due to how many were initially exposed or to how virulent a strain of the disease is at work.

She said pneumonia is the leading killer of bighorn herds infected with mycoplasma. In herds not infected, the leading cause of death is predators, mainly cougars, she said.

After WSU researchers identified the mycoplasma, biologists in Idaho, Washington, Oregon, California and the Canadian province of Alberta sent the researchers blood samples previously collected from 18 herds.

Researchers found antibodies to the mycoplasma in herds that saw deaths due to pneumonia, but not in herds that were not experiencing large losses due to pneumonia.

"We found some really promising patterns and things seemed to fit together really well," Cassirer said.

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