JOHNE'S DISEASE ALERT
L. Earl Rogers, D.V.M.
Utah Assistant State Veterinarian
Johne's disease is a disease of domestic and wild ruminants characterized by chronic wasting, diarrhea, and decreased production. It is caused by Mycobacterium paratuberculosis, a cousin of the organism which causes TB. Its relationship with Crone's Disease in humans remains uncertain. Young animals are most susceptible and infection occurs very early in life. Newborn calves often contract the infection from infected dams either in utero, through the colostrum, or from fecal contamination (dirty udders, etc.). The organisms localize in the intestinal tract and associated
lymph nodes followed by an extremely long period of incubation. Clinical signs are often not seen until they are made evident by the stress of the first, second or third calving (or some other stress). The animals will then show loss of production, weight loss, chronic diarrhea, and chronic wasting in advanced cases. Animals often shed the organisms prior to the onset of clinical signs and may develop subacute or chronic forms of the disease in which they continue to shed organisms for life.
The disease is a significant problem in cattle in the northeastern U.S. Many of those states, including New York, Pennsylvania, Ohio, and Wisconsin, have established extensive control and eradication programs. The incidence of disease in those states has been estimated at 10-30% of the dairies. Wisconsin has implemented an "implied warranty" law wherein all cattle offered for sale are implied to be free of Johne's disease unless accompanied by test results or a disclaimer stating that the cattle are not warrantied to be free of the disease. Most cattle are sold under the disclaimer.
Wisconsin farmers who are interested in controlling the disease will not buy cattle that are unwarranted and as a result, those cattle may be sold to dealers who then resell them out of state. Purchasing those cattle exposes the dairyman to disease risk. Even the purchase of springers who show no clinical evidence of the disease does not limit the risk. Young cattle that are asymptomatic may have been calfhood infected and serve to carry the disease to the new premises.
The best protection against introduction of the disease is to purchase replacements from known herds that are certified free of Johne's disease. Total herd certification is more reliable than individual animal testing. There is a National Johne's Disease Certification Program which is voluntary. It is of benefit to both buyer and producer when considering the purchase or sale of replacements. It involves whole herd testing of adult animals at 12-14 month intervals. Each negative herd test advances the herd to a new level of certification over a series of five negative tests. A positive test is
cause for decertification. Many states have adopted variations of the National Program. A National Johne's Disease Eradication Program is also in the developmental stages.
Johne's Disease is an expensive disease both in terms of production and control. In addition to the obvious lost production there are losses associated with culling affected animals, including offspring of affected animals. There are hidden losses associated with retention of less productive individuals (who would otherwise have been culled) in order to compensate for animals removed from the herd due to Johne's disease. Whole herd testing is expensive, running about $7-10 dollars per test. It is estimated that for every clinically evident diseased animal in the herd there may be as many as 20-30 other animals in various stages of the disease that are affected. This is called the "iceberg" effect.
Identification of animals in the early and later stages of the disease can be very difficult, yet these animals continue to spread the infection to other animals. Most attempts at eradication of the disease from an infected herd require a minimum of 5 years, although this time can be shortened with aggressive culling and testing. Prevention is definitely preferable. The Latin phrase "caveat emptor" (let the buyer beware) definitely applies here.
Johne's disease is present in Utah. It is a reportable disease when diagnosed. The Department of Agriculture has dealt with several infected herds in the last year. The incidence of the disease in Utah is unknown, but I am sure the "iceberg" effect is present here, too. For every reported case there are several that go undiagnosed or unreported. Control efforts involve testing and culling of affected animals and their offspring. Equally important are sanitation management actions such as preventing fecal contamination of feed and water, immediate separation of newborn calves from their dams
prior to nursing, feeding colostrum from a non-infected source, feeding of milk replacer, complete separation of all young animals from adults, adequate manure management procedures, spreading manure on croplands rather than pastures, etc.
As eradication programs for diseases such as brucellosis and tuberculosis are nearing completion, attention is shifting to other important diseases such as Johne's disease, bovine leukosis, and others. Most of these programs are voluntary in nature and industry driven. Awareness is the starting point. Education is the process. Regulatory mandate is becoming less necessary. This information is presented in that context. If we at the Utah Department of Agriculture may be of service please contact us at (801) 538-7161.