News and Highlights: May 2006

New test for Johne's Disease (Paratuberculosis)

CWH researchers S. Eda, and M. C. Scott and C.A. Speer have recently developed a novel test for detecting Johne’s disease in livestock and wildlife, with very high levels of diagnostic sensitivity and specificity:    [March 24, 2006 Media Release]

Johne’s disease, caused by Mycobacterium avium subsp. paratuberculosis (MAP), is a chronic intestinal disease occurring in a broad range of livestock and wild animals.  Because of their economic importance, the disease has been primarily studied in cattle and sheep but wildlife are considered as possible sources of infection for livestock.  The USDA estimates that approximately 22 percent of all dairy herds and eight percent of all beef herds in the U.S. have Johne’s disease causing an annual loss of more than $200 million to the dairy industry alone.

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Recent findings suggest that MAP may cause Crohn’s disease in humans. Crohn’s disease is a chronic and recurrent inflammatory gastrointestinal disorder characterized by inflammation and ulceration of the intestinal tract.  In severe cases, Crohn’s disease patient’s activities in daily life are limited due to abdominal pains, frequent diarrhea, and hospitalization.  The Crohn’s and Colitis Foundation of America currently estimates that there are more than 0.5 million patients with CD in the U.S.  Since some reports show that MAP organisms might survive pasteurization, dairy milk is suspected as a source of MAP infections in human.

Wild and free-ranging ruminants, such as sheep, deer, goat, antelope, elk, and bison, are also susceptible to Johne’s disease.  MAP infections have also been identified in some non-ruminant species, including rodents and primates.  Although the effects of MAP infections on wildlife health and population dynamics are largely unknown, several reports indicate the occurrence of cross-contamination of MAP between wild and livestock animals.  In Scotland, lizestock grazing areas and pastures have been found to be contaminated with rabbit feces containing MAP.  Further studies of MAP infections in wildlife are needed to evaluate impacts of MAP infections on wildlife health and to develop a better understanding of MAP transmission among wildlife and livestock.

MAP infections in wild animals have been studied by culturing the organism from fecal samples or by using enzyme-linked immunosorbent assays (ELISA) developed for diagnosis of Johne’s disease in cattle. Because of the slow-growing nature of MAP, the fecal culture test requires 5-16 months to complete and is capable of detecting less than 50% of MAP-infected animals.  Current commercial ELISAs are capable of detecting only 13.5-45% of fecal-culture-positive animals.  Therefore, it is likely that the prevalence of MAP infections in wildlife are greatly underestimated. Clearly, there is an urgent need for a rapid and highly sensitive diagnostic method for Johne’s disease in wildlife as well as livestock.

Speer, Eda and Scott have recently developed a novel ELISA for detecting Johne’s disease in cattle that has levels of diagnostic sensitivity and specificity higher than 95%.  The UT test for Johne's is rapid, safe, and easy to conduct.  Based on this discovery, two patents are pending, three papers have been published in international journals, and a license agreement has been made between the University of Tennessee and a major veterinary diagnostic company.  Using the new ELISA, CWH researchers are now studying the prevalence of Johne’s disease in wild and free-ranging animals.  Since the new ELISA for Johne’s disease is substantially more sensitive and specific than current ELISAs, studies by the CWH group will contribute to a better understanding of MAP infections passed between wildlife and livestock.

Recent publications on this research:

Eda, S.; Elliot, B.; Scott,M.C.; Waters, W.R.; Bannantine, J.P.; Whitlock, R.H. and Speer, C.A. 2005. New method of serological testing for Mycobacterium avium subsp. paratuberculosis (Johne's Disease) by flow cytometry. Foodborne Pathogens and Disease 2(3): 250-262. [PDF]

Speer, C.A.; Scott, M.C.; Bannantine, J.P.; Waters, W.R.; Mori, Y.; Whitlock, R.H.; Eda, S. 2006. A novel enzyme-linked immunosorbent assay for diagnosis of Mycobaterium avium subsp. paratuberculosis infections (Johne's Disease) in cattle. Clinical and Vaccine Immunology 13(5): 535-540. [PDF]

Other Johne's Disease links :

Johne's Information Center (University of Wisconsin)
USDA APHIS Johne's Disease website

Other Center for Wildlife Health news