Biologists investigate sick bighorn sheep in Nevada

LAS VEGAS — Wildlife biologists want to determine why desert bighorn sheep in the River Mountains of Southern Nevada are falling ill and will have to euthanize some to find the answer.

Biologists fear that some of the herd that lives in the rocky terrain between Henderson and Lake Mead may have contracted pneumonia, an often-fatal disease in wild sheep.

Wildlife experts and members of the public have observed sheep coughing and sneezing, but biologists said the symptoms alone are not enough to make a reliable diagnosis because they could also indicate a less threatening illness.

“A runny nose is one thing but pneumonia is another,” said Dr. Peregrine Wolff, state wildlife veterinarian. “The only sure way to make a firm diagnosis is to test samples from all tissues while testing for all pathogens, especially those that we know have caused pneumonia.

“Unfortunately, taking samples with cotton swabs or through blood samples is not enough,” she said. “This situation requires that we complete a full necropsy on at least one sick adult and perhaps a couple that are young of the year.”

The Nevada Department of Wildlife said biologist will need to euthanize one or more animals to conduct thorough testing.

Sheep carcasses found in River Mountains have tested positive for a bacteria, Mycoplasma ovipneumoniae. Biologists said that bacteria and another, Pasteurella, is strongly associated with pneumonia outbreaks in populations of free-ranging bighorn sheep through the western U.S.

“An in-depth study of a few sheep is important to help us understand a disease process that could potentially impact a sheep herd that is important to all of Nevada,” Wolff said.

About 250 bighorns make their home in the River Mountains, Doug Nielsen, NDOW spokesman, said Friday. The herd has played a central role in a decades-long program to bring back wild sheep herds around the state.

When the wildlife agency began its trapping and transplant program in 1967, there were fewer than 3,000 bighorn sheep statewide. Their numbers now top 11,000, Nielsen said.

“This particular herd has been our transplant source,” he said. “If it turns out there is pneumonia, it would obviously be devastating to our program.”