Barry Whitworth, DVM
Area Food/Animal Quality and
Health Specialist for Eastern Oklahoma
In 1895, Dr. F. Harmes was presented with a cow that exhibited symptoms of weight loss and diarrhea. He initially diagnosed tuberculosis (TB), but when the cow was tested for TB, the tuberculin test was negative. Upon the death of the cow, he sent some tissue samples to the pathology unit at the veterinary school in Dresden, Germany. Dr. Heindrick A. Johne and Dr. Langdon Frothingham examined the samples. The small intestine was thickened, and the lymph nodes were enlarged. These lesions were considered to be tuberculosis type lesions. The two scientists performed another TB test which again was negative. The two-scientist proposed that another mycobacterium was causing the disease. Today the disease is known as Johne’s disease, and the bacterium is classified as Mycobacterium avium subspecies paratuberculosis, commonly referred to as MAP. MAP is a very hardy microorganism in the environment. MAP is resistant to heat, cold, moisture, and drying. The bacterium has been found to survive for several months in the soil and water. The organism can be found in grasses fertilized with contaminated manure.
Johne’s disease, which is pronounced “yoh-nees,” is a gastrointestinal disease of ruminants that is fatal. Producers should be aware that Johne’s is a herd disease. This means that if one animal is found ill with MAP then several more of the normal appearing animals are probably also infected with the organism. Most animals are infected with the disease early in life, but the clinical symptoms of the disease do not appear for many months. The organism is contagious. The bacterium can be transferred animal to animal within a species such as cow to cow or from one ruminant to another ruminant such as cattle to sheep. Non-ruminant species (dogs, pigs, raccoons, coyotes, etc.) can also be infected with MAP, but they usually to do not have any clinical signs. In the United States, it is estimated that 91% of the dairy herds and 7.9% of beef herds are infected with Johne’s.
Cattle are usually infected with MAP at an early age. The organism can be found in fecal material, milk or colostrum of infected cows. Calves may ingest the organism by nursing fecal contaminated teats or by nursing milk or colostrum infected with MAP. They also may ingest the organism by eating feed, grass or drinking water that is contaminated with MAP. One other way that calves may be infected is in the uterus of infected adults. Adults are not as easily infected with the organism but still can be infected with MAP by ingesting contaminated feed, grass, or water.
The length of time between being infected with MAP and the appearance of clinical signs is variable. Cows may become sick in as little as two years, or it may be several years before clinical signs appear. The speed at which the animal shows clinical signs depends on how many organisms were ingested initially. If the calf ate a large number of bacteria, then it will be more likely to show clinal signs sooner than if a small number were ingested initially. Not only does the number of ingested bacteria play a role in the disease, but scientists have found a genetic connection. Some cows are more resistant to infection than others. Even so, all breeds of cattle are susceptible to MAP.
The two most common clinical signs seen in cattle with Johne’s disease are diarrhea and weight loss. MAP infects the last portion of the small intestines and its lymph nodes. With the thickening of the intestinal wall, nutrients cannot be absorbed, which results in malabsorption diarrhea. When an animal cannot absorb nutrients, it will break down its body to supply the nutrients needed to survive. Most cattle will have good appetites but continue to lose weight. The cows will become weak and emaciated. Another clinical sign that some cows display is submandibular edema or “bottle jaw.” “Bottle jaw” is caused by low serum protein levels. Protein is important to maintain vessel structure in the body. As serum protein values drop, fluid begins to leak out from the vessels.
All mycobacteria microorganisms are difficult to treat. For example, to cure human tuberculosis it requires multiple antibiotics given for long periods of time. Studies in cattle indicate similar results. Improvement was seen when antibiotics were given; however, once treatment was discontinued, the cattle would relapse. The drugs needed to treat Johne’s disease are not currently approved for cattle. If the drugs were approved, the cost would make treatment economically not feasible.
The best way to keep Johne’s out the herd is prevention. Producers must work to prevent positive cattle from entering the herd. Replacement bulls and cows should be purchased from Johne’s free herds or test all new introduction.
Read more in the January issue of Oklahoma Farm & Ranch.