Wyoming
Wolf pup numbers fall drastically due to outbreak of contagious virus
Dire wolves had their first playdate
The three dire wolves created using fossil DNA had their first official hang just months before their first birthday.
An outbreak of a contagious canine disease, particularly fatal for young pups, impacted the gray wolf population in Wyoming and Yellowstone National Park in 2025, with only an estimated “31 to 34” of the 87 documented pups born surviving until the end of the year.
Canine distemper, a contagious measles-like virus, was detected in 64% of animals in northwestern Wyoming, where wolves are classified as “trophy game.” While most adults are able to survive the affliction, the disease can be lethal for pups, with a 37% survival rate at the end of the year.
However, the wolf population in Wyoming “remained above minimum recovery criteria, making 2025 the 24th consecutive year Wyoming has exceeded the numerical, distributional, and temporal recovery criteria established for wolves by the U.S. Fish and Wildlife Service,” according to the 2025 annual report from Wyoming Gray Wolf Monitoring and Management.
At least 253 wolves in approximately 37 packs were noted statewide in Wyoming, including the Wolf Trophy Game Management Area, Yellowstone National Park and the Wind River Reservation on Dec. 31, 2025, according to the report. The state does not have management authority in the latter two areas.
Sixty wolves were reported to have died in WTGMA with causes of deaths including hunting (28), conflict control (16), other human causes (4), natural causes (8) and unknown causes (4), the report said. While the number was lower than in 2024, “the wolf population in the WTGMA decreased by 19% as a result of reduced pup production and recruitment,” the report said.
What is distemper?
Distemper is a “contagious viral disease that infects species such as domestic dogs, coyotes, foxes, raccoons, skunks, and wolves,” according to the Wyoming Game and Fish Department. The virus attacks the respiratory, gastrointestinal and nervous systems of dogs and other wild canines including foxes and wolves, according to the American Veterinary Medical Association.
While the disease can impact canines of all ages, puppies are at a higher risk.
Symptoms include discharge from the eyes and nose, fever, coughing, lethargy, vomiting and diarrhea. As the virus attacks the nervous system, canines may also exhibit neurologic signs such as walking in circles, inability to follow a straight path, lack of coordination, muscle twitches, seizures and even partial or complete paralysis.
Distemper can be spread through airborne exposure to the virus from an infected dog or wild animal through sneezing, coughing, or barking, AVMA said, and can also be transmitted through shared food, water bowls and other items.
Once infected, dogs spread the virus in body fluids like respiratory droplets, saliva or urine, and may be contagious for several months. Infected mother dogs can pass the virus to their unborn puppies.
Increase in wolf population density likely impacted distemper rate
In the report, Wyoming Fish and Wildlife said an increase in wolf population density in the WTGMA in 2023 “appears to have contributed to increasing distemper rates in 2024 and 2025.”
“Disease presence and prevalence in wildlife populations is generally density-dependent, meaning the risk of a particular disease impacting a population increases as population density increases,” the report said, adding “wolves are no exception,” and distemper infections “are highest in wolf populations at high population and wolf pack densities.”
The report also described the virus as a “common, naturally-occurring infection which cycles through areas with carnivore populations and has been documented in Yellowstone at least five times since 1995.”
Gray wolves in Wyoming
Gray wolves were introduced in Yellowstone National Park in 1995, under the U.S. Fish and Wildlife Service Endangered Species Act “with the goal of reestablishing a recovered gray wolf population in thenorthern Rocky Mountains.”
“The wolf population expanded quickly in number and distribution throughout northwest Wyoming,” the report said. “The population met the required recovery criteria by late 2002 and has exceeded the recovery criteria every year since.”
The Northern Rocky Mountains population was delisted in 2011, while Wyoming was delisted in 2017. Remaining wolf populations in the contiguous United States were delisted in 2021 “due to recovery,” FWS said.
Saman Shafiq is a trending news reporter for USA TODAY. Reach her at sshafiq@usatodayco.com and follow her on X and Instagram @saman_shafiq7.