Severe pneumonia outbreak kills bighorn sheep

Lamb survival to be closely monitored for several years

Another overview story about the bighorn sheep die-offs around the west. Estimates of the death toll have reached 1000 bighorns.

Severe pneumonia outbreak kills bighorn sheep.
American Veterinary Medical Association


  1. Drew Avatar

    question: Is this viral or bacterial pneumonia? If bacterial, which type? If viral, is it mycoplasma? Thanks

    1. Ken Cole Avatar

      The actual agents haven’t been identified. It could be one, it could be a combination, or it could be different in each outbreak.

  2. Drew Avatar

    Thanks! I assume lung tissue cultures form culled animals a being done so you should have the answer soon. Please update that info.

    1. Ken Cole Avatar

      You can find the recent report on the outbreaks and what they have found here:

  3. Drew Avatar

    Thank you again.

  4. TC Avatar

    Minor correction – Mycoplasma ovipneumoniae is a bacterium, not a virus. Viral pneumonia generally does not kill bighorn sheep – one or more viruses (RSV, PI3, etc.) may predispose the animals to secondary bacterial pneumonia, that may cause significant disease or mortality (dependent on bacterial species – the most virulent usually being Mannheimia haemolytica). Lungworms, stress, inadequate nutrition and other factors also have some role in large outbreaks of respiratory disease in this species. The jury is still out on how Mycoplasma affects bighorn sheep populations – not known if it is significant pathogen capable of killing many animals, if it predisposes to more virulent bacterial infections, if it will affect survival and lamb recruitment, etc. And finally – isolating one or more potential pathogens from tissues is not definitive evidence that the agents caused the death of that animal – it’s just what it is, the result of one diagnostic test that should be interpreted in light of all field and laboratory findings.


Ken Cole is a 5th generation Idahoan, an avid fly fisherman, wildlife enthusiast, and photographer. He is the interim Idaho Director for Western Watersheds Project.

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Ken Cole