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 the Ranch Comprehensive Management Plan (Ranch CMP), park staff has been working in collaboration with the Johne's Testing Center (JTC) at the University of Wisconsin and collecting elk fecal samples for Johne's disease testing from the Drakes Beach and Limantour herds since May of 2014. As of March 22, 2016 we have collected 547 fecal samples and have received results on 487 samples. (Samples take eight weeks to culture, so results on the additional 60 samples are pending.) Three bull elk from the Drakes Beach herd tested positive for the bacterium that causes Johne's disease from the November 2015 fecal collections; 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. Between October 2015 and March 2016, 27 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 up to twelve tissue samples and one fecal sample to the JTC for Johne's disease testing through a culture method of detection. As of March 22, 2016 we have received all results on the Drakes Beach herd and no results from the Limantour herd. Two bulls from the Drakes Beach herd tested positive for the presence of the bacterium that cause Johne's disease. The tests were confirmed through a genetic analysis. We may be able to better understand the origin of Johne's disease in the Drakes Beach herd by comparing the genetics of the bacteria found in the bull elk with those found in the elk at Tomales Point. Over the course of the next year, we will continue to monitor for the presence of Johne's disease in the Drake Beach herd through regular fecal collections and necropsies of any freshly discovered elk carcasses.
Q. Are you seeing animals symptomatic of Johne's disease (i.e. weight loss and diarrhea) at PRNS?
A. No. We have not encountered any animals with physical symptoms of Johne’s disease.
Q. What is the risk of transmission of Johne's disease between tule elk and cows?
A. The risk of Johne's disease transmission is greatest in areas of high animal density where manure accumulates and soils become wet and muddy. For the most part, elk and cattle intermix within open pasture and rangelands in the pastoral zone of Point Reyes, and the risk of transmission is low.
Q. How will these results affect the Ranch CMP?
A. We began the testing for Johne's disease in May 2014 to inform the Ranch CMP, and this is important information that we will be incorporating into the plan. Johne's disease is known to occur at Point Reyes and this result is not unexpected. This finding informs but does not change the timeline of the planning process.
Q. Do we know whether the tule elk have carried Johne's disease since their re-location to Limantour in 1999 or were subsequently infected by cattle within the pastoral zone?
A. We do not know the source of the bacteria in the two bulls that tested positive for Johne's disease at Drakes Beach. Further genetic studies may help to answer this question.
Q. Why did you do tissue sampling for Johne's disease?
A. Tissue samples from the gut have a higher sensitivity to testing than fecal samples. In fecal samples, an animal may be infected but not actively shedding the bacterium, creating a false negative result. Johne's disease is a difficult pathogen to test for and false negative results are not uncommon in all of the available testing methods.
Q. How will these results impact discussions with the California Department of Fish and Wildlife (CDFW) about moving tule elk out of the park in order to reduce the impact to park ranching operations?
A. We are exploring that topic with the CDFW now.
Q. Can humans get Johne's disease? Is there a public health risk?
A. No. The term "Johne's disease" is used only to describe the clinical illness in ruminants that occurs after infection from the Johne's bacterium.
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 http://escholarship.org/uc/item/2wt3h3rc (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 http://www.jwildlifedis.org/doi/pdf/10.7589/0090-3558-39.2.323 (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.