Brucellosis in Wyoming Wildlife

Brucellosis is a bacterial disease primarily of Rocky Mountain elk and bison. The disease is limited to northwestern Wyoming and adjoining portions of Montana and Idaho. Cows often abort their first fetus after becoming infected. Abortions may occur in subsequent pregnancies but diminish over time. The disease does not affect bull reproduction; however infection may result in inflammation of the testes (orchitis). Brucellosis also infects domestic cattle. A state/federal eradication program has almost eliminated the disease in cattle, but infected elk and bison pose a continuing threat.
How Does Brucellosis Affect Me?
Brucellosis is a zoonotic disease. Humans, including hunters, usually become infected by handling the infected reproductive tract or fetus. Hunters should always wear protective gloves when field dressing, especially during late season (January). Reproductive organs, placentae, or swollen testes or joints should not be opened. Symptoms include recurring (undulant) low-grade fever, joint or back aches, night sweats, and depression. Such symptoms can occur weeks or months after exposure and often are not related back to the handling of an infected animal. Symptoms can be successfully treated with a prolonged course of antibiotics. Failure to treat brucellosis can result in lifelong debilitation.
Brucellosis Impacts on Wildlife

The prevalance of brucellosis can be quite high (up to 75% in bison), yet there is no evidence that brucellosis has noticeable impacts on populations. The primary management concern is the possible transmission of brucellosis from elk or bison to domestic cattle. States having infected cattle herds suffer economic hardships. The threat to cattle results in ongoing friction among wildlife management agencies, ranchers, and federal agencies.


Brucellosis in Wyoming

Brucellosis interactive map

Hunter-Harvested Surveillance

Each year the Wyoming Game and Fish Department (WGFD) monitors the distribution of brucellosis within the state’s elk populations by requesting hunters to collect blood samples from their harvested animal.  Surveillance is generally concentrated in elk herds that surround, but do not use state or federal feedgrounds.  Nearly a quarter of the state is surveyed each year, eventually providing coverage over the entire state.  Currently, approximately 8,500 blood collection kits are assembled and mailed to hunters successful in acquiring limited quota elk licenses within target surveillance areas.  In general, hunters return between 1,200 and 1,500 blood samples to the laboratory, of which approximately 60% are suitable for testing (samples often freeze in the return mailing, rendering them untestable).

2022 Non Feedground Elk Brucellosis Report
2021 Non Feedground Elk Brucellosis Report
2020 Non Feedground Elk Brucellosis Report
2019 Non Feedground Elk Brucellosis Report
2018 Non Feedground Elk Brucellosis Report
2017 Non Feedground Elk Brucellosis Report
2016 Non Feedground Elk Brucellosis Report
2015 Non Feedground Elk Brucellosis Report

Since 1991 over 12,500 elk blood samples have been analyzed for brucellosis.  To date, this disease has only been documented in the western half of Wyoming, with prevalence levels between 0-4% in the southern herd units (South Wind River, West Green River) surrounding feedgrounds, and between 1-23% in the corresponding northern herd units (Clarks Fork, Gooseberry, Cody, and Wiggins Fork).  The northern units have been opportunistically monitored for the past several years, where historical prevalence was similar to the southern herd units, but for unknown reasons dramatically increased in early 2000.  

Brucellosis Raffle Info

Bighorn Mountains

In 2012, two sero-positive elk were discovered on the west side of the Bighorn Mountains; nine additional sero-positive elk have been discovered in the BIghorn Mountains between 2013 and 2016.  Intensive surveillance of the Bighorn Mountains will continue for the forseeable future as part of the statewide hunter harvested elk brucellosis surveillance.  Enhanced surveillance also focuses on both blood and tissue collection, with tissues being collected from hunter harvested animals by WGFD employees in an attempt to document culture positive elk. The documentation of sero and possibly culture positive elk outside of the Greater Yellowstone Area (GYA) is of great concern to both livestock and wildlife managers. 

Bighorn Mountains Enhanced Elk Brucellosis Surveillance Program Report - April 2017
Bighorn Mountains Enhanced Elk Brucellosis Surveillance Program Report - April 2018
Bighorn Mountains Enhanced Elk Brucellosis Surveillance Program Report - March 2021

Bighorn Mountains Elk Movement Study

To better understand the ecology of brucellosis and elk in and around the Bighorn Mountains, particularly how brucellosis moved into and is sustained by elk in the region, an elk movement study was initiated in early 2016 to: evaluate movement and interactions of elk herds in the Bighorn Mountains; determine route of brucellosis spread to the Bighorn Mountains; identify calving areas; and model how brucellosis may spread further if it becomes established. Understanding the route of spread will enable development of management strategies that could minimize further spread to neighboring elk herds as well as exposure to domestic cattle.  Initially, 61 elk were collared in 2016; another 59 elk were collared in 2017 and up to forty more elk will be collared in 2018.  Nine of the elk initially collared in 2016 were harvested by hunters.  Hunters will not be fined and are not in trouble if they legally harvest a collared elk. The Wyoming Game and Fish Department asks that hunters do not cut, discard, or destroy the collars.  Simply remove the nuts and bolts where the collar overlaps, or remove the elk's head and slide the collar from the neck, and return collar to a WGFD employee or office.  Please contact the Cody Regional office with any questions.  The video below compiles some of the elk movement data from this study.



Wyoming Game and Fish Department Brucellosis Information and Guidelines for Risk Reduction

Elk Herd Brucellosis Management Action Plans
Feedground Brucellosis Reports
USDA Animal and Plant Health Inspection Service
Wyoming Department of Agriculture
Wyoming Livestock Board

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