Johne's disease, or Paratuberculosis, is a chronic infection of the intestinal tract of ruminants. Infections have been found in cattle, sheep, goats and some species of wild ruminants. Johne's disease is caused by a species of bacteria known as Mycobacterium Paratuberculosis.
The major known method of spread is fecal-oral; this means the animal usually ingests the bacteria through feed or water contaminated with infected feces. In calves, this may occur when they first nurse their dam. Apparently, there is an age-related resistance to Johne's Disease. Calves under one year old are most susceptible. Older heifers are less susceptible and adult cows are resistant to infection. Other possible, though less common, routes of infection include semen (via natural service) and pregnant dam to fetus (in utero).
The exact answer to this question is unknown. For example, separate slaughter surveys have indicated that as few as 2 percent to as many as 17 percent of culled Ohio cattle may be infected with Mycobacterium Paratuberculosis. While many individual herds are undoubtedly free of infection, some herds may harbor the infectious agent in 50 percent of the adult animals.
Following exposure, some animals apparently "clear" the bacteria and remain totally free of infection. Others may become infected and periodically shed bacteria in their feces but never develop clinical signs of the disease. Some herds, however, may lose 5-10 percent of their adult cattle annually to clinical Johne's.
For those cattle that are exposed and eventually develop clinical signs, Johne's Disease is different than many other diseases. The time from exposure to development of signs is long and may range from 1-13 years. It is common for heifers to develop Johne's signs following the stress of the first or second freshening.
The initial clinical sign is the development of diarrhea. The diarrhea may be either continuous or of an intermittent nature. In addition to diarrhea, there is extreme weight loss and, eventually, death. Some animals may have a low-grade fever and develop edema under the jaw as diarrhea progresses. There is some evidence which indicates that animals with subclinical Johne's (i.e. without diarrhea) may experience reduced milk production and suboptimal fertility.
Obtaining a rapid, reliable diagnosis is possibly the major problem in controlling Johne's Disease. Basing the diagnosis of a herd entirely on clinical signs could be misleading. Other disease agents can cause a similar type of diarrhea. Furthermore, an animal could be shedding Johne's bacteria (Mycobacterium Paratuberculosis) in its feces, contaminating the environment, yet be visibly normal.
Currently, the most reliable diagnostic test is the bacteriologic culture of feces. A drawback to the fecal culture is that is doesn't allow detection of infected animals that are not shedding bacteria. Another drawback is the time it takes to determine the results, 12-18 weeks.
Two serum tests, AGID and ELISA are available; currently, both have serious shortcomings. The AGID test is very accurate when an animal has clinical Johne's, and many veterinarians use AGID to obtain an early diagnosis on a suspect diarrheic animal. This test has a 48 hour turnaround; an advantage over the 12-18 week time-lag with fecal cultures. For use in herd control programs, AGID is not sensitive when an animal is infected but visibly normal: AGID is likely to misclassify a shedding or non-shedding animal that is still clinically normal as negative.
The ELISA tests currently available falsely classify some noninfected animals as infected and some infected animals as noninfected. Hopefully, improvements in test methods and standardization will enhance the usefulness of the ELISA.
In the future, other improved tests may be developed for practical use in diagnosis. For example, DNA probes for detection of Mycobacterium Paratuberculosis in feces have been developed and used experimentally. At this time (September 1988), work is being completed to determine how applicable DNA probes will be for diagnostic use and in herd control programs.
The Johne's bacteria is very resistant to antibiotics. Treatment of animals with Johne's is not advisable. Generally, the most economically sound decision is to market clinically affected cattle as soon as possible. Johne's infected cattle will usually pass slaughter if they are not severely thin or debilitated.
In the environment, Mycobacterium Paratuberculoses is extremely hardy. It can survive in soil, manure and water for more than a year. It is resistant to many common disinfectants. On clean surfaces, however, it is quickly destroyed by direct sunlight. As with most other infectious diseases, there is no substitute for cleanliness when considering Johne's control.
A vaccine is available. In Ohio, it must be administered by an accredited veterinarian. Permission and guidelines for its use on a farm must be obtained from the State Veterinarian. The vaccine helps reduce shedding of bacteria and clinical signs when coupled with good management. The vaccine will not totally prevent infection, however. As with many other diseases, vaccination may be a portion of a disease control or reduction program but not the total answer.
No official federal or Ohio programs exist at the present time. Several other states do have programs in place. Most programs, in addition to stressing hygiene and management, rely upon periodic fecal culturing to identify shedding animals and subsequent culling of these animals from the herd. Some states allow vaccination; others do not. It is too early to tell how effective these programs will be.
First assess the probability or extent of additional infected animals present in your herd. For example, was the affected cow purchased as a springing heifer or raised as a natural addition to your herd? If she was home-raised, given the fact that infection occurs early in life, there is a likelihood that additional herd mates have been exposed. If she was purchased as a springer and not exposed to your farm's young stock it is possible that spread may not have occurred. Your veterinarian may or may not recommend additional herd testing at the time of the initial diagnosis depending on the circumstances.
Total eradication of Johne's, given currently available diagnostic tests and knowledge, may not be economically feasible in commercial herds. However, a more intensive intervention program may be warranted in herds that merchandise breeding stock. Herds that can demonstrate test-negative status may command premiums on animals offered for sale or export. Regardless of your herd's present infection status, institution of a control or prevention program does make economic sense in all dairy herds.
Reduce exposure of susceptible animals. In any Johne's control or eradication program, complete commitment and cooperation between herd owners, managers, caretakers and veterinarians is vital.
Management Recommendations for Control of Johne's Disease in a Dairy Herd.
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This page was last updated on November 16, 2002