Johne's Disease FAQs

Johne's disease, or paratuberculosis, is an infectious and incurable gastrointestinal disease caused by a bacterium found in domestic and wild ungulates. An infected animal may appear healthy, with symptoms of weight loss and diarrhea not showing from many months to years later. Johne's disease is primarily a problem for ruminant species—hoofed mammals that chew their cud and have a 3–4 chambered stomach. Common ruminants are cattle, sheep, goats, deer, antelope, elk, and bison. Johne's occurs most frequently in domestic agricultural herds: an estimated 68% of dairy herds and 8% of beef herds in the United States contain at least one infected animal (University of Wisconsin, Johne's Information Center). Johne's disease is typically spread from one animal to another through infected feces. An infected animal sheds the organism in feces onto a pasture or into water shared by the herd. Young animals are far more susceptible to infection than are adults, and swallow the organism along with grass or water. See the Johne's Information Center for more details.

A 1979 study documented the presence of Johne's disease in 5 of 10 dairy herds tested at Point Reyes National Seashore (PRNS) (Riemann et al.). The disease has been documented in tule elk at Tomales Point Elk Reserve during the course of several studies since 1980 (Jessup et al. 1981, Manning et al. 2003, Cobb 2010). Johne's disease has been detected in axis and fallow deer at Point Reyes (Riemann et al. 1979), and several studies have documented Johne's in North American deer species, suggesting that black-tail deer at Point Reyes are potential carriers of the disease.

To better inform ongoing tule elk management, park staff have worked in collaboration with the Johne's Testing Center (JTC) at the University of Wisconsin to test elk fecal samples from the Drakes Beach and Limantour tule elk herds beginning in 2014. A small number of bull elk from the Drakes Beach herd tested positive for the bacterium that causes Johne's disease, while all other samples were negative.

Johne's disease is a difficult pathogen to test for and false negative results in fecal samples are not uncommon. Beginning in 2015, elk were collected from the Drakes Beach and Limantour herds and taken to the California Animal Health and Food Safety (CAHFS) Laboratory at UC Davis for full necropsy and higher sensitivity Johne's testing. For each animal, CAHFS sent tissue and fecal samples to the JTC for testing through a culture method of detection. A small number of bull elk from the Drakes Beach herd tested positive for the presence of the bacterium that causes Johne's disease.


Frequently Asked Questions


Literature Cited

Cobb, M.A. 2010. Spatial Ecology and Population Dynamics of Tule Elk (Cervus elaphus nannodes) at Point Reyes National Seashore, California. University of California, Berkeley. Available at (accessed on 30 January 2016).

Jessup, D.A., B. Abbas, D. Behymer and P.J. Gogan. 1981. Paratuberculosis in tule elk in California. Journal of the American Veterinary Medical Association 179:1252–1254.

Manning, E.J.B., Kucera, T.E., Gates, N.B., Woods, L.M. and M.Fallon-McKnight 2003. Testing for Mycobacterium avium ss. paratuberculosis infection in asymptomatic free-ranging adult tule elk from an infected herd. Journal of Wildlife Diseases 39(2):323–328. Available at (accessed on 30 January 2016). (110 KB PDF)

Riemann, H., M.R. Zaman, R. Ruppanner, O. Aalund, J.B. Jorgensen, H. Worsaae, and D. Behyer 1979. Paratuberculosis in cattle and free-living exotic deer Journal of the American Veterinary Medical Association 174:841–843.

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Last updated: March 8, 2024

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