Maryland Department of Agriculture

What is Johne’s disease?
Johne’s disease is a chronic (years) mycobacterial infection that affects principally the lower small intestine of many ruminants. Cattle, sheep, goats and less frequently deer, llamas, bison, and other ruminants are all susceptible to the disease. Johne’s disease usually refers to the clinical condition associated with the mycobacterial infection, whereas the term “paratuberculosis” usually refers to the state of being infected with the causative organism, M. paratuberculosis but not necessarily having clinical signs.

More than 90 percent of animals infected with the bacteria causing Johne’s disease appear like normal healthy animals, but may serve to spread the infection to other ruminants. Clinical signs of Johne’s disease, which include weight loss and diarrhea with a normal appetite, only become apparent in the later stages of the disease. Signs are rarely evident until two to several years after the initial infection, which usually occurs soon after birth. Other than loose consistency, the manure appears normal. Several weeks after the onset of diarrhea, a soft swelling may occur under the jaw (bottle jaw). Bottle jaw or intermandibular edema is due to protein loss from the bloodstream into the intestinal tract. Animals at this stage of the disease will not live very long, perhaps a few weeks at the most.

What causes Johne’s disease?
The causative agent of Johne’s disease, M. paratuberculosis, is an acid-fast bacterium related to cattle and swine tuberculosis organisms and other mycobacteria that are present in the environment. Mycobacterium paratuberculosis was first isolated in 1895 by Dr. Heinrich Albert Johne, hence the name “Johne’s” disease (pronounced “yo-knees). Like other mycobacteria, this is a slow-growing organism which requires 12-14 weeks to grow in the laboratory.

How does Johne’s disease occur?
The most likely time for infection to occur is at or soon after birth. The most frequent way newborn calves become infected is by swallowing small particles of infected manure from the calving environment, or from the teat or udder of the dam. In addition, calves can be infected while in utero or they can ingest bacteria which can be passed in the colostrum or milk. Slaughter studies have shown that as many as 25 percent of calves were infected in-utero if the pregnant cow had clinical signs of Johne’s disease. The risk of infection to the calf by any of these three routes increases as the cow enters more advanced stages of the disease.

After infection, the bacteria grow slowly in the intestinal lining cells and cause gradual thickening of the intestinal mucosa. These changes impair normal absorptive function and result in weight loss and diarrhea. Eventually, protein nutrients leak directly from the blood stream into the intestine causing low blood protein and bottle jaw.

Which animals are susceptible to Johne’s infection?
Calves or young animals are more susceptible to infection with Johne’s disease than adult animals. Although animals develop some resistance with age, cattle or animals of any age can be infected when introduced into an infective environment, particularly where animal density is high or where feed or water can be contaminated with manure from infected animals. All breeds of cattle, sheep, and goats are susceptible to Johne’s disease. However, Johne’s disease occurs more often in dairy than beef cattle.

When do clinical signs of Johne’s disease develop?
Even when animals are infected at a very young age, clinical disease rarely appears before two years of age. Animals exposed at an older age (18- 24 months or older), or exposed to a very small dose of bacteria at a young age, are not likely to develop clinical disease until they are much older than two years. Some animals may not show clinical signs for 10 years or more. Age at the time of first exposure and/or the number of organisms ingested is the major factors that determine when clinical disease will develop. Observations suggest that animals tolerate paratuberculosis infection better under conditions of good nutrition and husbandry. Different species also display variations in clinical signs. For example, sheep and goats typically show weight loss but rarely develop diarrhea.

What are the stages of Johne’s disease infection in cattle?
There are three stages of Johne’s disease or paratuberculosis in cattle:

STAGE I: Silent, subclinical, non-detectable infection --- typically this stage occurs in all calves, heifers, and youngstock less than two years of age and many adult animals exposed to small doses of disease-causing organism. Infected animals at this early stage are rarely detected with currently available diagnostic tests, including fecal culture or serologic tests (ELISA). This stage progresses slowly over many months or years to stage II.

STAGE II: Subclinical infection—typically this stage occurs in older heifers or adults. Animals at this stage appear healthy but are shedding adequate numbers of M. paratuberculosis organisms in their manure to be detected on fecal culture. Blood tests will detect some, but not all animals at this stage. Blood test (ELISA) positive animals should be confirmed positive by fecal culture. These animals pose a major but often hidden threat for infection of other animals through contamination of the environment.

STAGE III: Clinical Johne’s disease—any animal with advanced infection, the onset which is often associated with a period of stress, such as recent calving. Cattle at this stage have intermittent, watery pea-soup manure. Animals lose weight and gradually drop in milk production but continue to have a good appetite. Some animals appear to recover but often relapse in the next stress period. Most of these animals are shedding billions of organisms and are positive on culture. Most are positive on serologic tests (ELISA & AGID). Clinical signs often last several weeks to months before the animals are sent to slaughter in a thin, emaciated condition.

In the final and terminal aspects of stage III of the fatal disease, animals become emaciated with fluid diarrhea and develop “bottle jaw”. The carcass may not pass meat inspection for human consumption in the later phases of stage III.

“The Iceberg Phenomenon” – Infection in the Herd
In the typical herd, for every animal in stage III (showing clinical signs), many other cattle are present in the earlier stages of the disease. For every stage III cow expect:

Stage III	Clinically diseased	1-2 cows
Stage II	Unapparent carrier adults	6-8 cows
Stage I	Infected calves-youngstock	10-15 cows

For every obvious clinical case (stage III) of Johne’s disease on the farm, 15-25 other animals are likely infected. The clinical case represents only the “tip of the iceberg” of the Johne’s infection. However, only 30-40 percent of all infected cattle can be detected with even our most sensitive fecal culture technique. Thus, in a herd of 100 milking cows, two clinical cases at one time suggest 20-30 others are infected, and less than half of the infected cattle are detectable by fecal culture. If 25-30 animals are fecal culture positive on a single herd (100 adults) fecal culture test, it is likely that at least 50 percent of the cattle in the herd are infected.

The iceberg phenomenon illustrates the key concept in recognizing the potential impact that Johne’s disease can have on a herd. That is, if the infection remains unchecked, the rate and number of infected animals in the herd increases progressively over time. Early diagnosis and prevention of spread, before multiple clinical cases have surfaced, can avoid the development of Johne’s disease into a significant herd problem five to ten years into the future.

How common is Johne’s disease?
The 1996 Dairy National Animal Health Monitoring System’s (NAHMS) study estimated about 22 percent of the nation’s dairy herds were infected with Johne’s disease. Larger herds (>300 cows) are more likely to be infected (40 percent) compared to about 20 percent for small herds (<50 cows). In Maryland, it has been estimated that more than 35 percent of our herds are infected with an estimated 10 percent infection rate of our adult dairy cattle. The numbers are likely to be less for beef cattle and beef farms. As dairy herds expand it is even more important to ask potential sources of herd additions, if they have had Johne’s disease on their farm. Replacements for expanding herds should originate from Johne’s negative herds.

How is Johne’s disease detected?
In the living animal, fecal culture IS the most accurate diagnostic test, but requires 12 to 14 weeks culture time and is expensive. Various serologic tests including ELISA and AGID detect antibody in the serum and can be used on a herd basis or to confirm clinical cases. They are less accurate than culture but are rapid and less expensive. In the dead animal, Johne’s disease is accurately diagnosed by culture and histopathology of the lower small intestine (distal ileum) and associated lymph nodes. For further information about available diagnostic tests, contact your local veterinarian or one of the Maryland Department of Agriculture’s Animal Health Diagnostic laboratories listed in this pamphlet.

What is the economic impact of Johne’s disease?
The economic impact of Johne’s disease in a herd may include some or all of the following effects:
1) premature culling of exposed, infected, or clinical animals leading to: a) reduction in culling for other reasons, such as low production, other health problems, etc.
b) loss of valuable animals and genetic potential
2) decreased milk production in infected animals (losses of 5-20 percent)
3) loss of marketing and show opportunities
4) possible breeding problems in infected animals
5) veterinary costs

In a 1983 study of culled Pennsylvania dairy cattle, 7 percent of the animals were infected. Infected animals yielded an average of $54 less due to reduced weight at slaughter and produced an average of 3,400 pounds less milk for the last lactation than negative culled cattle. Based on this study, a conservative estimate of the loss attributed to Johne’s disease for Pennsylvania dairy cow industry was $5.8 million per year. The total losses attributable to Johne’s disease were estimated to exceed $1.5 billion annually for the cattle industry in the Untied States. Surveys have indicated that Johne’s disease is also common in many other states, including Wisconsin, New York, Maryland, Ohio, Virginia, Illinois, Florida, Connecticut, California, and Texas.

The 1996 Dairy NAHMS report found that in herds where at least 10 percent of the cull cows had clinical signs of Johne’s disease, the average cost to producers was $227 for each cow in the herd per year. For example, in a 100 cow dairy with at least 10 percent of the cull cows with signs of weight loss and diarrhea, the loss to the herd would be about $23,000 each year. The majority of this was due to decreased milk production. On a national basis, this suggests an estimated loss of $200 million for the U.S. dairy industry.

How is Johne’s disease controlled on the farm?
There is no practical medical treatment for Johne’s disease. The key to preventing, controlling, and eliminating Johne’s disease in a herd is good biosecurity practices. Testing (fecal culture) is a valuable tool to evaluate the extent of the infection in the herd, to identify infected animals, and to monitor progress of control efforts. The general strategy for controlling infection is to identify and adopt appropriate biosecurity procedures for the individual farm that will best accomplish three main goals:

1. Protect highly susceptible newborn calves and young animals from ingesting manure from infected adults, whether from the dam, from the environment, or from contaminated feed or water.
2. Prevent all other susceptible animals from ingesting low levels of infected manure, especially by preventing contamination of feed and water.
3. Reduce the total farm exposure level to M. paratuberculosis by reducing the number of infected animals that are shedding the bacteria.

Goals one and two are achieved by good sanitation and accepted biosecurity practices, which benefit the farm as a whole. Goal three is accomplished by more rigorous testing and culling of infected animals. For a given level of infection, detecting and culling infected animals in the earlier stages of the disease will speed the rate at which Johne’s disease is reduced or eliminated from a herd.

Specific recommendations:
The specifics and intensity of a Johne’s disease control strategy for cattle will vary by the individual farm situation. To be relevant and effective, the program must be designed to fit the immediate and future goals of the farm, and available resources.

Many specific methods can be used to accomplish the three main management goals. The most effective and practical measures to break the cycle of infection and disease in the herd are outlined.

Management of newborn calves and young animals is critical and is the most effective area to focus the control effort:
• Calves should be born in an area that is dry, clean of manure, and well-bedded. Calving areas should be used only by one or a few animals at a time and for maternity ONLY. Clean teats and udders at calving time are essential to prevent manure ingestion by the newborn calf.
• The most effective control measure is to remove newborn calves from the dam and maternity area immediately, thus ELIMINATING attempts by the calf to nurse and thus eliminating the chance of ingesting infected colostrum or manure on the teat
• Feed newborn calves colostrum, ideally within one to two hours. Use only colostrum from healthy dams (preferably Johne’s negative cows), who are least likely to pass M. paratuberculosis into the udder and milk. Pooling colostrums and waste milk both promote and amplify the spread of Johne’s disease and must be avoided.
• Milk replacer eliminates the risk of possible infection from feeding whole or pooled milk to calves. Use of a good quality milk replacer should be seriously considered, especially in herds with significant infection.
• Young calves and heifers should be housed separately from adults and should have no direct contact with manure from adult cattle. Separate facilities are ideal, but calf pens protected by partitions, dry alleyways, or buffer zones, or low traffic zones are effective.
• Do NOT contaminate feed or feed mangers with manure from equipment or feet of farm personnel. Manger sweepings must not be fed to heifers or young stock, as this will help spread Johne’s disease.

Management to prevent low levels of exposure in all older animals is important:
• Prevent manure contamination of feed and waters. DO NOT use the same loader or equipment to remove manure and then load feed. DO NOT walk in the feed bunks.
• Eliminate or fence animals out of natural drinking water sources that are slow moving or stagnant, that collect run-off containing manure or that animals stand in.

Identifying and removing infected animals and their manure is necessary to reduce the risk of continued exposure for all animals:
• Test the herd to identify infected animals that are, or probably will be, shedding the disease-causing bacteria. Based on evaluation of test results, infected animals should be culled as quickly as economic consideration permit. The most severely infected animals should be culled first.

An initial fecal culture test of the whole herd followed by aggressive culling is very effective in initially reducing the prevalence in the herd. Appropriate management should be started at the same time. Testing and culling, combined with biosecurity, will control Johne’s disease more effectively, and in less time, than either measure alone. Frequency of testing and culling will depend on what is practical for the farm. The simplest and most effective approach to take in any infected herd is to manage all animals as if they are infected and assume all manure is guilty. This management attitude works and is especially important if testing and early culling is not practical.

• Attempt to recognize and cull animals with suspicious clinical signs earlier, before they further contaminate facilities and lose salvage value. These animals are shedding billions of organisms each day. If you are uncertain, ISOLATE, or cull anyway and test to confirm infection status.

• SANITATION has no substitute. Remove manure as thoroughly and as often as possible. Always strive for more often. Spread manure on cropland, in accordance with your nutrient management plan, not on pasture to be harvested or grazed the same season.

Reduce the risk of introducing infected animals into the herd, especially when elimination of infection is the goal:
• Be cautious and investigate animals to be purchased. Purchase animals from test negative herds or herds with no history of Johne’s disease. Reduce risk by testing prior to purchase with serology or by fecal culture when animals arrive at the farm.

What are the goals of a Johne’s disease control program?
In herds with low to moderate infection (one percent or fewer clinical cases per year), wise use of a combination of testing, culling, and management can be expected to reduce the number of clinical cases to zero within one to three years and to eliminate most infection in five to seven years. As the herd turns over, each succeeding generation will have fewer infected animals, all of which will eventually be non-shedders. Complete elimination of infected cattle is likely to take many years after Johne’s disease becomes invisible in the herd, but it can be done. Biosecurity practices should remain in place, otherwise Johne’s disease is likely to recur.

With a negative herd test, your herd can qualify for U.S. Johne’s Disease Herd Status Program for Cattle. This program was adopted by the United States Animal Health Association in October 1998.

Herds with severe widespread infection will require aggressive control programs and many years to eliminate Johne’s disease. However, a practical control program and sound herd management can be expected to eliminate clinical disease in these herds and reduce the economic impact of Johne’s in the herd to a minimum.

For more information on control programs, contact:
Dr. Virginia Pierce
Maryland Department of Agriculture
Frederick Animal Health Diagnostic Laboratory
1840 Rosemont Avenue
Frederick, Maryland 21702
301-600-1548

USDA/APHIS
Area Veterinarian in Charge
410-349-9708

Resources
More information can be found on the USDA Animal and Plant Health Inspection Service (APHIS) website: http://www.aphis.usda.gov/vs.

Reproduced with permission by the Animal Health Commission, Pennsylvania Department of Agriculture