Since the reintroduction of gray wolves in Wyoming — both inside and outside of Yellowstone National Park — about 30 years ago, this species has faced one battle after another, including public opposition, trapping, and poaching. But disease has also played a role in some of the struggles wolves have faced in these areas.
Per the Wyoming Game and Fish’s 2025 wolf monitoring report, canine distemper significantly affected wolf pups in the park, leading to low reproduction and a population decline to its lowest level since the wolves were reintroduced.
This isn’t the first time these wolves have faced this disease, and it likely won’t be the last. Here’s how it will likely impact them.
Canine Distemper in Wyoming’s Wolves
Canine distemper can be very unpredictable. Even though outbreaks can follow multi-year cycles, the disease can sometimes appear irregular or at random. For wolves, when population numbers begin to grow, outbreaks can become more common.
In 2025, wolf researchers went out into the field to capture and test wolves for canine distemper. The team predicted, based on computer models, that the infection rate would be about 28 percent. However, according to the report, 64.3 percent of the captured wolves tested positive for distemper, much higher than researchers had predicted based on historical patterns.
Of the wolves surveyed, many came from outside of Yellowstone National Park, particularly in the Wolf Trophy Game Management Area (WTGMA). This area had a population of almost 200 wolves in 2023, which could have increased opportunities for disease transmission.
According to the report, the virus had its greatest impact on wolf pups. Of the at least 87 wolf pups born in 2025, only 31 to 34 survived — a survival rate of about 37 percent. Some of the wolf packs affected had no surviving pups. The WTFMA saw a roughly 19 percent population decline in 2025.
Canine Distemper Symptoms
Canine distemper is a contagious disease caused by a virus, according to the American Veterinary Medical Association. The virus typically attacks a canine’s gastrointestinal, respiratory, and nervous systems, and while canines of all ages can contract it, puppies are at higher risk.
Because the virus can affect multiple body systems, the symptoms can vary widely. Gastrointestinal and respiratory symptoms include discharge from the nose and eyes, coughing, fever, loss of appetite, and vomiting. Nervous system symptoms include muscle twitches, coordination loss, jaw-chewing and drooling, head tilting, walking in circles, and seizures.
The virus can be spread from animal to animal through airborne particles from sneezing, barking, or coughing. It can also be spread through shared water and food sources.
Besides dogs, other mammals, such as ferrets, foxes, skunks, raccoons, and wolves, can contract this virus.
Read More: Viruses Could Cause Wolves to Change Colors
Canine Distemper in Yellowstone Wolves
Though the WTGMA surrounds and extends beyond Yellowstone National Park, there is little to no direct evidence that the park's wolf population contracted distemper. However, there is indirect evidence.
Of the 36 wolf pups born in the park, only 17 survived — a survival rate of only 47 percent. This is the lowest pup recruitment since 1996, right after wolves were reintroduced to the park. These patterns suggest disease — possibly distemper — may have played a role, but more evidence is still needed to confirm.
Per the report, there are at least 84 wolves still living in Yellowstone among 7 packs, with 3 breeding pairs, while there are at least 132 wolves still living in the WTFMA area, with about 22 packs and 10 breeding pairs. Ideally, though, for the WTFMA, management would like to see that population number around 160 individuals.
For now, officials with the park and the Wyoming Game and Fish Department will continue to monitor the situation and set up management plans to keep wolf populations in Wyoming healthy.
"Wolf populations generally rebound quickly after a population decline," Ken Mills, a wolf management specialist with the Wyoming Game and Fish Department, told Discover. "This has consistently been the case for similar disease outbreaks in Yellowstone National Park, based on their research. We anticipate implementing a more conservative wolf hunting mortality limit in 2026 because of the population decline, but we expect the population to still be at or near our population objective at the end of 2026."
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article includes information from the Wyoming Game and Fish’s 2025 wolf monitoring report
- This article includes information from the American Veterinary Medical Association: Canine distemper
