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• Johne's disease or paratuberculosis must be managed as a herd problem and not treated as an individual cow disease.
• Diagnosis of one clinically-infected animal in a herd of 100 lactating cows implies that at least 25 other animals are infected and less than eight of those can be detected by the tests currently available.
• Long-term goals, economic capacities and managerial abilities of the dairy enterprise must be considered when developing a herd-specific control program.

What's in a name?

Johne's disease (pronounced "yo-knees") was first identified by two veterinary scientists (H.A. Johne and L. Frothingham) over 100 years ago in Germany. The first reported cases in the United States were described in 1908 by Leonard Pearson, VMD. The organism responsible for Johne's disease is Mycobacterium paratuberculosis. This name gives the disease its medical classification of paratuberculosis. The prefix "para-" means "apart from" hence, paratuberculosis should be considered separate from tuberculosis. While both are caused by a mycobacterium, the two diseases have very different afflictions. Tuberculosis primarily causes respiratory lesions and has known human health implications. Through the federal eradication program, bovine tuberculosis has been nearly eliminated from the United States. Bovine paratuberculosis is associated with chronic diarrhea and weight loss in infected cattle. Voluntary national guidelines have been established to certify low risk herds. The public health concerns are currently being investigated.

Johne's spreads like warm butter.

Mycobacterium paratuberculosis typically inhabits the intestinal tract and intestinal lymph nodes of infected cattle. It is now known that the organism can disseminate throughout the body to other sites including the uterus, supramammary lymph nodes, udder, and sexual organs of bulls. This leads us to believe that milk and semen of infected cattle can transfer the organism to susceptible animals. It also appears that as the infection progresses to a clinical stage (chronic diarrhea and weight loss), the likelihood of disease transmission increases.

One of the most insidious aspects of this disease is the ability of the organism to migrate across the uterus into a growing fetus. In pregnant cows showing advanced stages of infection, 20 to 40 percent of fetuses will become infected. Asymptomatic cows can also transmit Johne's to their fetuses but at a lower frequency (8 to 9 percent). Fetal infection appears to be associated with the number of organisms shed in the feces of infected cows. The potential for prenatal transmission should play a key role when purchasing herd replacements and making culling decisions. Pregnant, heavily-infected, symptomatic cows should not be permitted to remain in the herd in hopes that a negative calf will be born.

Johne's disease is primarily acquired by ingestion of M. paratuberculosis from a contaminated environment. Infected cattle begin to shed organisms in their feces after several years (2-3) of incubation. At first, the number of organisms is barely detectable, but fecal shedding gradually increases so that symptomatic cattle shed billions of organisms each day. Mycobacterium paratuberculosis can persist in the environment for up to a year. It has been cultured from manure slurry storage, soil of pastures, streams and pond water, as well as maternity pens and exercise lots. Any piece of equipment stained with feces should be treated as contaminated. Newborn calves are highly susceptible and establishment of infection may be related to age, dose of organisms ingested, and level of resistance to disease. Older cattle can become infected (particularly in highly stressed cattle in a heavily contaminated environments), but it is less common. Colostrum and milk of heavily infected cows (shedding many organisms in their manure) will contain M. paratuberculosis up to 35 percent of the time. Asymptomatic cows can shed the organism in their milk and colostrum as well, but less frequently. Calves should not be fed milk or colostrum from cows known to be infected.

All tests are NOT created equal!

Identification of Johne's-infected cattle can become an overwhelming task. Choosing the proper diagnostic tests and understanding the strengths and weaknesses of each test can alleviate some of the futility. There are basically two types of tests; those that detect the organism and those that detect the body's reaction to infection by the organism (antibodies). False-positive reactions (positive test results when in truth the animals are not infected) are rare for nearly all test methods. Unfortunately, false negative results (negative test results when in truth the animals are infected) are fairly common. This is particularly true because of the long incubation period before clinical signs develop. Other reasons for false negative results include infected cattle which have not mounted a sufficient immune response and cattle shedding low numbers of organisms. Fecal or tissue culture and genetic (DNA) probe tests detect the organism while complement fixation (CF), agar gel immunodiffusion (AGID), and enzyme-linked immunosorbent assay (ELISA) detect serum antibodies to M. paratuberculosis.

Fecal or tissue culture has been the "gold standard" for identification of Johne's-infected cattle. The primary advantage of this method is that it detects cattle actively shedding M. paratuberculosis and thus those more likely to transmit the disease. Unfortunately, the culturing process requires much technical expertise and results may not be available for 4 to 12 weeks depending on the laboratory. Also, asymptomatic cattle and those shedding very few organisms may yield false-negative results. The genetic (DNA) probe test also detects cattle actively shedding M. paratuberculosis. This technique identifies a specific section of DNA common only to M. paratuberculosis. The unique section is amplified by polymerase chain reaction (PCR) to aid detection. This test takes only three days to perform but is more expensive and highly technical. Genetic probes require more organisms for detection than fecal culture which unfortunately creates more false-negative reactions too.

Infected cattle produce antibodies to M. paratuberculosis during the late stages of infections, but usually before clinical signs develop. The antibody concentration required to create a positive result varies across test methods. The ELISA can detect much lower levels of antibodies than the AGID or CF test and is rapid and inexpensive. False-positive results are rare now that antibodies to cross-reactive environmental mycobacteria can be removed. The absorbed ELISA test has been licensed by the USDA and made into a kit for commercial use. Antibody detection techniques still have the disadvantage of false negative results particularly when the animals are not shedding in high numbers. Overall, the ELISA test appears to be able to detect nearly half of the infected animals in Johne's-infected herds. An added benefit of the licensed ELISA test is the ability to quantify the level of specific antibody instead of merely producing a positive or negative result. Animals with suspicious results can be targeted for further testing.

An ELISA test has been developed to detect M. paratuberculosis antibodies in the milk of infected cows. More false positive outcomes occur with this test because cross-reactive antibodies from other mycobacteria have not been removed. It appears to have similar sensitivity in that nearly half of the truly infected cows can be detected. One additional benefit is that the test can be performed on previously frozen milk and milk containing preservatives. Results obtained from testing bulk tank milk should be interpreted with caution. Obscure results can be obtained due to the number of infected cows in a herd, the amount of exposure to environmental mycobacteria, and the characteristics inherent in the test itself.

To control or not to control...Is THAT the question?

Fundamental to the control of Johne's disease is the understanding that paratuberculosis must be managed as a herd problem and not treated as an individual cow disease. Because infected cattle can shed M. paratuberculosis a long time before clinical signs develop, culling the occasional symptomatic cow is an inadequate means of controlling Johne's disease.

When designing herd-specific control programs, the business objectives of the dairy enterprise as well as the producer's management abilities and long-term goals must be considered. Johne's disease can cause a 7 to 25 percent reduction in milk yield and may shorten the productive life of a cow. Significant economic impact may not be felt by commercial producers purchasing herd replacements, provided the number of infected cows remains below five percent. Dairy producers raising their own replacements may have more reasons for concern. Indebtedness and cash flow of the dairy enterprise are critical factors to consider in test and cull control programs. Producers who intend to exit the dairy business in the near future may not want to commit to the expense and management changes required to control paratuberculosis.

The initial step in a Johne's disease control program is to determine the herd prevalence (the number of infected cows in the herd). If all replacement animals are home-raised, it can be assumed for every clinical cow there are likely 5 to 10 subclinically infected animals in the herd. With current tests (fecal culture or ELISA), the proportion of the herd truly infected is generally twice the number of positive test results (assuming all animals two years and older were sampled). Once the number of infected cows is established, the most economical control program can be developed.

The second step in a control program is to survey the management practices on the farm. The critical window of susceptibility is roughly the first six months of life. The primary mode of transmission is ingestion of an infective dose of M. paratuberculosis organisms. Emphasis should be placed on manure management and contact between calves and adult cows.

Finally, a herd-specific control program should be implemented. Record keeping is essential to monitor progress. The Johne's control program should be consistent with the long-term goals, economic capacities and managerial abilities of the dairy enterprise.

National Paratuberculosis Certification Program

Excerpted from: Whiple DL. Proceedings of the 97th Annual Meeting of the US Animal Health Association, Las Vegas, NV. 1993. pp. 311-316.

1. Herd definition

A. All cattle under common ownership or supervision that are grouped on one or more parts of any single premises (lot, farm, ranch).

B. All cattle on two or more premises geographically separated but on which cattle have been interchanged or where there has been contact between the premises. Contact of animals between separated premises under common management shall be assumed to have occurred unless otherwise established by the herd owner or manager.

2. Certification levels

Level 1: Herd test negative after one sampling

Level 2: Herd test negative after two samplings

Level 3: Herd test negative after three samplings

Level 4: Herd test negative after four samplings

Level 5: Herd test negative after five samplings

Level 5 monitored: Herd test negative after six or more samplings

3. Criteria for herds qualified to enter certification program

A. The herd has been in existence for at least one year.

OR The herd was assembled with cattle originating directly from certified herds only shall start at the lowest certification level of the herds from which the assembled cattle were acquired. A negative first herd test will qualify the newly assembled herd for the next certification level.

B. A herd assembled with cattle originating directly from certified herds only shall start at the lowest certification level of the herds from which the assembled cattle were acquired. A negative first herd test will qualify the newly assembled herd for the next certification level.

4. Animal identification

A. All animals must have permanent identification other than a plastic ear tag or neck chain.

B. Acceptable means of permanent identification are registration or association numbers accompanied by identification document, ear tattoos, USDA uniform series ear tag (metal tags), and electronic identification.

5. Animals to be tested

A. For annual certification: All cattle 24 months old and older are required to be tested.

B. For cattle being removed from the herd: All cattle being removed from the herd that are exhibiting clinical signs of Johne's disease.

C. For cattle being added to the herd: A negative serum antibody test is required before arrival on the premises and a fecal sample for M. paratuberculosis detection must be submitted to a laboratory no later than 15 days after arrival.

6. Testing interval

A. Certified herds are to be tested every 14 months (+/- 2 months).

B. Herds not tested within 16 months of the last sampling will lose their certification status. The next negative herd test will qualify the herd for Level 1 certification.

7. Testing laboratories

A. All tests for the National Paratuberculosis Certification Program must be performed at an accredited laboratory. Laboratory accreditation will be on the basis of satisfactory performance on an annual check test for serum antibody, M. paratuberculosis detection-based tests, or both. Precise mechanisms for conduct of annual check tests remain to be determined.

8. Test samples to be collected

A. For annual certification

1. Levels 1, 3, and 5: Blood for the detection of serum antibodies against M. paratuberculosis (i.e., ELISA test).
2. Levels 2 and 4: Feces for the detection of M. paratuberculosis (i.e., fecal culture).
3. Level 5: Monitor either type of test at the option of the owner.

B. For cattle being removed that are showing clinical signs of Johne's disease: Both blood for serum antibody testing and feces for organism detection.

9. Tests

A. Serum antibody test: Any test sufficiently sensitive and specific for detection of antibodies to M. paratuberculosis in bovine serum. Definition of "sufficiently sensitive and specific" will be on the basis of results of performance of a check test and proficiency standards set by the program. (Note: It is recommended that the USDA-licensed ELISA for M. paratuberculosis be the test of choice early in the program.)

B. M. paratuberculosis-detection test : Any test sufficiently sensitive and specific for detection of M. paratuberculosis in bovine fecal samples. Definition of "sufficiently sensitive and specific" will be on the basis of performance of a check test and proficiency standards set by the program. Note: Early in the program it is recommended that fecal culture be the test of choice. Furthermore, fecal culturing should be done at laboratories that have demonstrated proficiency at performing this test.

10. Collection of samples

A. All blood and fecal samples are to be collected by, or under the supervision of, a licensed accredited veterinarian.

11. Veterinary certification

A. The veterinarian performing or supervising the collection of test samples is to certify that the samples collected were from the animals identified on the test documents.

12. Owner/manager certification

The herd owner/manager is to certify:

A. At the initial test date: That the herd has been in existence for at least one year or was assembled only from certified herds.

B. At each test date: That all animals 24 months or older were sampled and included in the herd test.

C. At each test date: A list identifying all animals previously tested but no longer in the herd.

D. At each test date: That all animals added to the herd since the last herd test were raised in the herd or tested at the time of arrival on the premises (see 5.C.).

E. At each test date: A written statement certifying that to the best of the owner's knowledge no animals that left the herd tested positive for paratuberculosis or were exhibiting clinical signs of Johne's disease.

13. Definition of a positive animal

A. An animal is defined to be positive, i.e., infected with Mycobacterium paratuberculosis, only if M. paratuberculosis is demonstrated by an organism detection test on tissues or feces of the animal.

14. Consequences of identification of a positive animal during a herd test

A. Identification of a positive animal during the certification herd test will result in the loss of certification status. The next negative herd test will qualify the herd for Level 1 certification.

15. Protocol to be followed if an animal is positive by a serum antibody test

A. An animal positive on a serum antibody test must be retested by an M. paratuberculosis detection test as soon as possible, but no more than 120 days after the date the blood was drawn for the serum antibody test.

B. The certified herd will maintain its present certification status pending the results of the M. paratuberculosis detection test.

C. A negative result on the M. paratuberculosis detection test will allow the herd to move to the next certification level.

D. If an animal is removed from the herd while waiting for serum antibody test results, a fecal sample shall be collected and submitted to a laboratory. The sample will be tested for M. paratuberculosis if the antibody test is positive.

E. Failure to retest the animal within 120 days will result in loss of certification status. The next negative herd test will qualify the herd for Level 1 certification.

16. Protocol if an animal sold from a certified herd is identified as positive

A. If an animal sold from a certified negative herd is identified as positive by an organism detecting test within 16 months of the date of sale, selling certified herd shall, within 120 days of being notified, conduct a herd retest of all eligible animals by both the serum antibody and organism detection tests.

B. The selling certified herd will maintain at its present certification status pending the results of the herd tests.

C. If the herd retest is negative, the herd will maintain at its "present" certification status. The herd owner/manager shall then have the option of maintaining his/her present test schedule or retesting his/her test date so that his next herd test is not due until 14 months after the retest.

D. If a positive animal is identified on this retest, the selling herd will lose its certification status. The next negative herd test will qualify the herd for Level 1 certification.

17. For special circumstances or appeals, an advisory board will convene to consider the facts and render a final decision.

CHECK LIST FOR JOHNE'S DISEASE CONTROL

Management at calving

• Calving pens are cleaned, sanitized and isolated away from the rest of the herd.
• Udders, flanks and perineal areas are clipped and washed with detergent.
• Calves are removed from cows as soon as possible--at least prior to nursing.
• Calves are immediately placed in hutches or separated from adult animals.
• Calves are only fed colostrum from cows which test negative to Johne's disease.

Management of replacement rearing

• Replacement heifers are raised separate from adult cattle until first calving.
• Calves are isolated for the first month and culled if the dam develops clinical signs.
• Calves are fed milk replacer or discarded milk from test-negative cows.
• Feeding equipment and tools are not used for manure handling.
• Calves and heifers are not exposed to manure from adult cattle.
• Heifers are not grazed on pastures previously occupied by adult cattle.

Management of adult cattle

• Manure contamination of feed handling equipment, bunks and tools is eliminated.
• Fresh, clean, manure-free drinking water is provided.
• Pasture streams, standing ponds and collections of surface water are fenced off.
• Manure is spread only on crop land, not on hay ground or pastures to be grazed.
• All cows are bred by artificial insemination.

Management of heavy shedders or cows showing clinical signs

• Cows determined to be heavy shedders or showing clinical signs are isolated.
• Cows with non-responsive cases of diarrhea are culled.
• Heavy shedders and symptomatic cows are culled as early as economically possible.
• Offspring from confirmed (or suspected) clinical cases are culled.
• Pens used by clinical cows are sanitized prior to subsequent use.
• Contact with manure from heavy shedders or symptomatic cows to the herd is eliminated.

General management considerations

• All adult cattle (two years or older) are tested at least once a year.
• At least every third herd test is performed by fecal culture.
• Positive results from blood tests are confirmed by fecal culture.
• Purchased replacements only come from herds which test negative for Johne's disease.
• Purchased replacements and herd bulls are tested negative prior to entering the herd.
• A complete record-keeping system is established to document the economics of the Johne's disease control program (clinical cases, cull prices, testing expenses, etc).