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They're bright, alert, maintain a healthy appetite, but the animals suffer from severe, chronic diarrhea and become emaciated. That's a typical description of animals affected by Johne's (pronounced YO-knees) or "para- tuberculosis," a fatal, untreatable disease that can affect any ruminant, including cattle, sheep, goats, camels and deer. Although Johne's is not a reportable or regulatory disease in Texas, in the future it could affect trade opportunities. "For years, Johne's was though to affect herds primarily in the northern portion of the U.S.," said Dr. Andy Schwartz, Johne's specialist for the Texas Animal Health Commission (TAHC). He said a l997 study by the USDA's National Animal Health Monitoring System (NAHMS), indicated that at least 8 percent--or more than 12,000 of Texas' 153,000 beef herds may have contracted the disease. A recent NAHMS survey of dairies showed that about 23 percent of the herds across the nation are infected. The increased interest in Johne's Disease has "spurred" the Texas cattle industry to explore and consider options and alternatives for a voluntary Johne's herd status program. The Texas Johne's Working Group is preparing to introduce a four-level cattle herd status program for cattle, adapted from the National Johne's Herd Status Program. When implemented, the state's voluntary status program will help identify herds at "low risk" for Johne's. Producers in the program may enhance their marketing potential by providing other producers with a healthy pool of animals. First described by Dr. Heinrich Johne of Germany 1895, the disease is also called "paratuberculosis," as it belongs to the tuber- culosis family of bacteria. Johne's progresses slowly, targeting the digestive system and often is unapparent until the animal is well into adulthood. By the time the animal shows clinical signs of illness, the disease may have spread to herd mates. "Johne's bacteria 'sets up shop' in the animal's white blood cells in the wall of the intestines," explained Dr. Schwartz. "The animal's body responds by sending in more white blood cells to combat the intruder, and eventually the intestinal walls thicken. Finally, the walls become so thick, the animal can't absorb nutrients, and it develops chronic diarrhea. Despite a healthy appetite, the animal finally wastes away, Other less obvious signs in the herd can include decreased fertility, lower weaning weights, animals that must be culled sooner, and increased feed costs without related weight gain." "Infected animals shed Johne's or the paratuberculosis bacteria in feces, milk, colostrum, and sometimes, even through the placenta to an unborn fetus in the uterus," said Dr. Schwartz. "Infected animals can shed the bacteria onto feed or grass, where it can be ingested. Once outside the body, the bacteria contaminates the ground and water, and although it doesn't multiply, it can live up to a year in the environment. Young animals, from birth to a year of age, are most susceptible to the disease, he said. If a herd is infected, "pooling" the colostrum and feeding it to newborns can accelerate the spread of disease through the herd. Dr. Schwartz explained that a vaccine for Johne's lessens the severe, clinical signs and shedding of bacteria, but instead of eliminating infection, it only "masks" or diminishes damage in the affected herd. The vaccine's use must have state approval, and a veterinarian is to administer the injection only to animals less than 35 days old. Tests for Johne's fall into three categories, he explained. The most common is a blood test that screens for antibodies to the Johne's bacteria. The second, a skin test, can detect cellular response. Although nearly four months are needed for incubation, the most accurate test results come from the third category, which involves culturing fecal material, lymph node or intestinal wall tissue from the animal. And, on the horizon are the high-tech Gamma Interferon test and a refined gene probe, both of which show promise for earlier disease detection. The Texas Veterinary Medical Diagnostic Laboratory (TVMDL) in College Station can run blood or culture tests, and another 25 to 30 laboratories in the U.S. are accredited by the USDA's National Veterinary Services Laboratory in Ames, Iowa. "No test currently available can reliably detect early infection, or illness in animals younger than two years old, unless the disease has overwhelmed the animal," said Dr. Schwartz. "As producers learn about the disease, some will be concerned about the animals they purchase and they should try to buy from clean herds." Dr. Schwartz said it's best to prevent infection, and there are management techniques that can reduce risk of introducing infection, or slow the spread of the disease in affected herds:
For more information about the Johne's voluntary herd status program, contact Dr. Andy Schwartz at 1-800-687-4603. |
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