Johne's Disease

What is Johne's Disease?

Johne's disease, a chronic (years) mycobacterial infection, affects principally the lower small intestine of many ruminants. Cattle, sheep and 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, where as the term "Paratuberculosis" usually refers to the state of being infected with the causative organism M. Paratuberculosis but not necessarily having clinical signs.

Clinical signs of Johne's include weight loss and diarrhea with a normal appetite. Signs are rarely evident until two to several years after the initial infection, which usually occurs soon after birth. Other than the 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 most.

How does Johne's Disease occur?

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

After infection, the bacteria grow slowly in the intestinal wall. These changes impair normal function and result in weight loss and diarrhea. Eventually, protein nutrients leak directly from the bloodstream 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. Species and breed probably vary in susceptibility and prevalence. For example, Johne's disease occurs more often in dairy than beef cattle, but the true reasons for such differences have not been studied.

When does clinical 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 ten years or more. Age at the time of first exposure and the dose or the number of organisms ingested are the major factors that determine when clinical disease will develop. Observation suggests 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 four stages of Johne's disease or Paratuberculosis in cattle:

Stage I — Silent, subclinical, non-detectable infection - typically this stage occurs in calves, heifers and young stock less than two years of age and animals exposed to a small dose of disease causing organism or at an older age.

Infected animals at this early stage cannot be detected with current tests, including fecal culture or new serologic tests (ELISA). This stage progresses slowly over many months or years to Stage II. It is possible that some animals resolve or recover from this early phase of infection.

Stage II — Subclinical shedders - 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 are not reliable to detect animals at this stage.

These animals pose a major but often hidden source of infection to other animals through contamination of the environment.

Stage III — Clinical Johne's disease - any animal with advanced infection, the onset of which is often associated with a period of stress.

Cattle at this stage have acute or sometimes intermittent, watery peasoup manure. Animals lose weight and drop in milk production but continue to eat. 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. Many are positive on serologic tests. Clinical signs often last weeks before the animals are sent to slaughter in thin emaciated condition.

Stage IV — In the final and terminal state of the fatal disease, animals become emaciated with fluid diarrhea and develop "bottle jaw." The carcass may not pass meat inspection for human consumption.

"The Iceberg Phenomenon" - Infection in the Herd.

In the typical herd, for every animal in Stage IV, many other cattle are present in the earlier stages of the disease:

For every stage IV cow expect:

Stage III — Clinically diseased ... 1-2 cows.

Stage II — Inapparent carrier adults ... 6-8 cows.

Stage I — Calves-young stock ... 10-15 cows.

Thus, for every obvious clinical case (Stage IV) 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 40-50% 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 once 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 50-60% of cattle in the herd are infected.

The "iceberg" 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 is Johne's Disease Detected?

In the, living animal, fecal culture is the most accurate diagnostic test, but requires 12-16 weeks culture time and is expensive. Various serologic tests including ELISA, AGID and CF detect antibody in the serum and can be used on a herd basis or to confirm clinical cases. They are less accurate than cultures 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 the Minnesota Veterinary Diagnostic Laboratory at 612–625–8787 or 800–605–8787.

How is Johne's Disease controlled on the farm?

There is no treatment for Johne's disease. The key to preventing, controlling and eliminating Johne's disease in a herd is MANAGEMENT.

Testing is a valuable tool to evaluate the extent of the infection in the herd, to identify infected animals, determine the necessary intensity of a control program, and to monitor progress of control efforts. The general strategy for controlling infection is to identify and adopt appropriate management and sanitation procedures for the individual farm that will best accomplish three main goals:

1. Prevent highly susceptible newborn calves and young animals from ingesting manure from infected adults, whether from the dam, from the environment, or from the 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 removing the bacteria from the environment and reducing the number of infected animals that are shedding the bacteria.

Goals one and two are achieved by sanitation and accepted good management practices, which benefit the farm as a whole. Goal three is accomplished by more rigorous sanitation and by testing and culling specifically for Johne's disease. 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 is reduced or eliminated from a herd.

Specific recommendations:

The specifics and intensity of a Johne's disease control strategy for cattle will vary with 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 measure 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 are essential.

The most effective control measure is to remove newborn calves from the dam and maternity area immediately, thus eliminating attempts to find the udder and nurse and the chance to ingest manure.

Feed newborns colostrum, ideally within one to two hours. Use only colostrum from healthy appearing dams, who are least likely to pass M. paratuberculosis into the udder and milk.

Milk replacer eliminates the risk of possible infection from feeding whole or pooled milk to calves. Use of 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 sections protected by partitions, dry alleyways or buffer zones, or low traffic zones are effective.

• DO NOT contaminate feed or feed mangers with manure from feet of farm personnel or equipment.
  Management to prevent low levels of exposure in all older animals is important:

  Prevent manure contamination of feed and water.

• DO NOT use the same loader or equipment to clean up manure and to 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 and/or that animals stand in.

For more information on control programs, contact the Minnesota Board of Animal Health 612–296–2942 — Ext. 27.