Disease Impacts

Verbenone packets on whiteback pine trunks.
Verbenone packets (white) on whitebark pine trunks help fend off mountain pine beetles.


All park residents struggle to survive - the immediate needs of food, water, and shelter are found in each inhabitant's community. Predators rely on prey to survive. Prey forage on the park's abundant flora. Various plant species rely on sun, water, and soil nutrients. These processes seem obvious and observable. Some impacts, however, are more difficult to quantify and observe. Disease plays a hidden role in all environments and impacts all species.

Yellow-rust growths on whitebark pine bough
Close-up of blister rust on whitebark pine bough


Blister Rust, Mountain Pine Beetles, and Whitebark Pine

Whitebark pine (Pinus albicaulis) is a slow growing, long-lived pine with five needles, usually found above 8,000 feet. These pines seem to thrive in high-elevation sites with poorly developed soil, high winds, and extreme temperatures. Their fat and protein-rich nuts provide critical food source for grizzly bears during the fall hyperphagia period.

In the past two decades the die-off rate of whitebark pine is unprecedented due to the combined effects of native mountain pine beetle, nonnative white pine blister rust, and changing climate conditions. In 2018, 39 percent of whitebark were dead and 30 percent attacked by beetles. Fifty-seven percent of live trees were infected with blister rust, and only 15 percent produced cones. Beetle activity and blister rust severity was greatest below 9,500 feet and on south-facing slopes. Blister rust was worst on larger diameter trees.

The pheromone verbenone has been applied in packets to selected pine trees to ward off the attack of mountain pine beetles. This treatment tricks the pine beetles into attacking another tree. While effective, these packets must be reapplied regularly and can only protect selected areas.

Herd of cow elk with a bull elk behind during the fall mating season
Herd of Elk during the fall rut.


Chronic Wasting Disease and Elk

Chronic wasting disease (CWD) is a naturally occurring prion disease of cervids (species in the deer family). The disease attacks the brain causing animals to become emaciated, display abnormal behavior and poor coordination, and eventually die. Since its 1967 discovery in a captive herd of mule deer in Colorado, CWD has increased and spread. CWD is now established in the southeastern portion of Wyoming with scattered pockets found in deer and elk herds closer to the park.

In October 2008, the Wyoming Game and Fish Department (WGF) reported that a three-year-old female moose from Star Valley tested positive for CWD, within 50 miles of Grand Teton National Park. When CWD is found within 60 miles of a park, the National Park Service directs a park to monitor deer and elk for clinical signs of the disease and submit test samples from all dead deer and elk. Consequently, park staff stepped-up surveillance efforts in collaboration with WGF personnel.

Bison cow nursing calf in a grass and sagebrush meadow.
Bison cow nursing calf.


Brucellosis and Bison

Bison (Bison bison), a species native to Jackson Hole, were extirpated from the area by the mid 1800s. In 1948, twenty animals from Yellowstone National Park were introduced to the fenced 1,500-acre Jackson Hole Wildlife Park near Moran. In 1963, after testing positive for brucellosis, all adult bison in the small herd were destroyed while nine vaccinated yearlings and calves remained.

Brucellosis is a nonnative, bacterial disease that induces abortions in pregnant cattle, elk, and bison. Cattle brought brucellosis to the Yellowstone area in the early 1900s and transmitted it to local wildlife populations. The bacteria that causes the disease, Brucella abortus, can be transmitted between animals if they come into contact with infected birth tissues. While brucellosis has not had a substantial effect on wildlife populations, it poses a financial risk to ranchers because it can reduce the reproductive rate and marketability of their animals. Billions of dollars have been spent to eradicate brucellosis from cattle in this country. In the United States, Brucella abortus only persists in the bison and elk populations of the Greater Yellowstone Area.

There have been no documented cases of bison transmitting brucellosis directly to cattle. There have been many documented cases where elk transmitted brucellosis to cattle. In both cases, transmission is possible and the likelihood increases during late winter when bison, elk, and cattle are more likely to share grasslands in the eastern part of the park. Currently there is no vaccine for brucellosis that is 100 percent effective, and testing procedures lack certainty. This disease continues to be controversial throughout the region.

Last updated: April 30, 2020

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