Overview

Johne’s disease is a chronic, progressive disease affecting sheep, goats and other grazing animals. It is caused by a slow‑growing bacterium called Mycobacterium avium subspecies paratuberculosis (MAP).

Infection damages the intestinal lining and reduces the animal’s ability to absorb nutrients. Over time, this leads to gradual weight loss despite eating well, declining body condition, and eventually severe diarrhea and death.

Johne’s disease is common around the world, including North America in domestic and wild ruminants.

It has been found in:

  • sheep
  • cattle (both dairy and beef)
  • goats
  • deer and elk
  • camelids (alpacas and llamas)
  • other wild or domesticated ruminants

Johne’s disease is considered endemic in North America, meaning it is commonly present within the animal population. In Ontario, a 2016 study found that 66.8% of dairy sheep flocks and 83.0% of dairy goat herds had at least one infected animal.

2 strains of MAP bacteria have been identified. The cattle strain is most prevalent in North America and commonly affects cattle, sheep and goats. The sheep strain is most prevalent in Australian sheep, although it infects sheep and other species in different regions of the world with a lower prevalence.

Clinically affected animals have:

  • lower body weight
  • shorter lives
  • fewer offspring born per year
  • lower litter weaning weights

Depending on the number of animals affected within a population, the disease can have a substantial negative economic impact.

Human health risk

Johne’s disease is not currently considered a risk to human health. While there has been research investigating the association of Johne’s disease in ruminants with Crohn’s disease in humans, research has not proven that Johne’s disease causes Crohn’s disease.

As a precautionary measure, human exposure to MAP can be minimized by consuming only pasteurized milk and milk products.

Clinical disease

Once infected, animals typically do not show signs of the disease for a long time, often for 2 to 4 years.

In cases where infection occurs in utero or in young animals, clinical disease may manifest as early as 18 months of age. During this period with no symptoms, animals are considered subclinical. These animals are infected and may start shedding the bacteria in their feces, contributing to transmission within the herd or flock.

Signs of disease

Only 5–10% of infected animals show signs of disease. As a result, Johne’s disease can remain undetected within a herd or flock while it spreads. When the disease becomes visible, common signs include:

  • gradual weight loss, often despite eating
  • poor body condition
  • dull fleece or rough hair coat
  • pale gums and mucous membranes
  • reduced milk production

An experienced producer may only notice subtle differences, such as animals being slightly thinner than their herd or flock mates. Clinically affected animals represent only a small proportion of the total number of animals that are infected within the herd or flock.

Other stressors, such as kidding or lambing, or concurrent conditions like mastitis may speed up the onset of more severe clinical disease. Chronic diarrhea develops in about 20% of cases and is more commonly observed in cattle. Once goats or sheep develop diarrhea, the disease has advanced, and the affected animal may soon become reluctant or unable to stand prior to death.

Other diseases to consider

Johne's disease can be difficult to distinguish from other chronic wasting conditions, including:

  • dental issues (such as incisor loss)
  • Maedi Visna
  • parasitism
  • internal abscesses associated with caseous lymphadenitis
  • nutritional deficiencies or poor feeding management
  • other chronic disease (such as chronic pneumonia)

Treatment

There is no cure for Johne’s disease. Consult with your veterinarian if you are seeing signs of Johne’s disease within your herd or flock to ensure they are not due to other treatable conditions.

Transmission

Infected animals shed high amounts of bacteria in their feces, contaminating the environment. Herd or flock mates become infected by ingesting feed or water contaminated with fecal material. Mature, infected stock is the primary source of infection for youngstock.

Infected sheep on pasture will contaminate that pasture for other grazing animals. Infected animals in a barn may defecate into feeders or waterers. Lambs and kids born into these contaminated environments are most susceptible to infection. Manure contaminated udders and wool tags, equipment, barn yards and bedding are all sources of infection to kids and lambs.

Johne’s disease does not spread through airborne droplets or semen.

Other methods of transmission

Does and ewes shed MAP bacteria into milk and colostrum, even if they appear healthy.

If the dam is showing clinical signs of Johne’s disease during pregnancy, fetuses are very susceptible to infection while still in the womb. These young animals once born may be infected with MAP and may develop clinical Johne’s disease at an earlier age.

Diagnosis

Several diagnostic tests are available for diagnosing Johne’s disease in live animals using blood or fecal samples. These tests vary in accuracy and recommended use.

Work closely with your veterinarian to select the most appropriate test for your specific situation. For example, an animal with low body condition may require a different test than that used for screening a large group of animals or evaluating new additions to the herd or flock.

The progression and characteristics of Johne’s disease can make it challenging to diagnose.

In early or subclinical stages, infected animals often have low bacterial burdens, do not shed MAP in feces and have limited immune responses, reducing the ability of a test to detect infection. Repeated testing over time combined with herd or flock level management, with veterinary support, is necessary for more accurate detection and control of Johne’s disease.

Thin animals are usually identified during routine handling or sorting and are culled from the operation, treated or euthanized depending on the cause and severity. Thin animals with no clear underlying cause are often culled without further investigation or a confirmed diagnosis. This can allow Johne’s disease to persist undetected within a herd or flock, potentially spreading over multiple generations before it is identified and addressed.

Post-mortem diagnosis

When a clinically ill animal dies, your veterinarian can do a post-mortem examination. This may help identify the cause of death, whether it is Johne’s disease or not.

Beyond individual diagnosis, post-mortem examinations are valuable for monitoring overall health status, preventing future losses and supporting informed decision-making in management and biosecurity practices.

Control and prevention

Good hygiene, biosecurity and management practices can help control Johne’s disease, but reducing the disease on your farm requires commitment. MAP is very hardy and can survive in the environment, soil, water and manure despite cold, heat or acidic conditions. These features make it difficult to control the environment.

Prevention is the cheapest way of managing Johne’s disease since it is costly to eradicate it if already established within a population.

To prevent Johne’s disease:

  • prevent new MAP infections, especially in youngstock
  • avoid introducing animals infected with MAP
  • remove animals that are shedding MAP

MAP can survive well in the environment and is very resistant to disinfectants. Tuberculocidal disinfectants are effective at killing MAP and should be used when disinfecting washable tools, feeding equipment and troughs.

Tuberculocidal products include:

  • bleach
  • hydrogen peroxide
  • alcohols
  • quaternary ammonium compounds

You must follow the instructions on the label when using any product and ensure the product has enough contact time to be fully effective against MAP.

No vaccine is currently licensed in Canada for Johne’s disease.

Prevention in youngstock

Manure

High amounts of MAP bacteria are shed in the feces of infected animals, and this is the largest source of infection for youngstock under 6 months of age. Hygiene and management practices that minimize youngstock exposure to manure are critical.

  • Keep pens where kids or lambs are born and raised clean and dry to reduce their contact with manure.
  • Clean water troughs regularly and remove and dispose of accumulated sediment in an area inaccessible to animals.
  • Pastures can be contaminated with MAP bacteria when manure from infected animals is spread.
  • Incorporate manure into the soil after spreading and avoid putting youngstock out on these pastures immediately, if possible. This reduces the risk of manure transmission through grazing or consumption of forages grown on contaminated land.

Milk and colostrum

Infected does and ewes may shed MAP in both milk and colostrum, even if they are not yet showing clinical signs. This route of transmission can be mitigated through the use of heat-treated colostrum, pasteurized milk or commercial milk and colostrum replacement products.

When using maternal colostrum, you can reduce the risk of MAP transmission by:

  • using colostrum only from does or ewes that have tested negative for Johne’s disease
  • avoiding pooling colostrum from multiple animals
  • thoroughly cleaning and drying the udder and teats before collection
  • properly cleaning and disinfecting all equipment used to collect and feed colostrum

In dairy goat and sheep production systems, when youngstock are reared artificially, it is possible to remove offspring from the pen of mature stock quickly after birth. This limits the time a young animal spends in an infected environment and limits contact with potentially infected herd and flock mates, reducing the risk of disease transmission.

Controlling new stock

Animals entering an operation should be tested prior to arrival to reduce the risk of introducing Johne’s disease into the herd or flock. It is easier to test and select negative animals before their arrival than to attempt eradication once it has become established. These preventive measures also apply to animals that are intended to join the herd or flock temporarily (such as breeding bucks or rams).

To minimize the risk of introducing Johne’s disease:

  • maintain a closed herd or flock whenever possible
  • buy animals from a limited number of reputable and known sources
  • source animals only from herds or flocks that undergo annual herd level Johne’s disease testing and get a copy of the testing results to ensure negative status
  • test animals prior to purchase and before arrival to your operation, in consultation with a veterinarian to ensure an appropriate test is used
  • buy youngstock from dams that have tested negative for Johne’s disease
  • closely evaluate the body condition of all the adult animals if diagnostic testing has not been conducted in the source herd
  • avoid introducing other susceptible species (such as cattle or other ruminants) that may carry Johne’s disease
  • do not borrow or lend animals (such as breeding rams)

Herd level eradication

Eradication programs are based on the ability to detect and remove diseased animals and to prevent the spread of disease within the herd or flock. You can design a testing program in consultation with a veterinarian. Programs are generally based on annual or semi-annual serological testing of all mature animals. Positive animals should be culled or isolated.

Youngstock from positive dams are considered at a high risk of being infected and should not be kept as replacements. Positive and high-risk animals should not be sold where there is a chance of selling them for breeding stock (such as auction barns).

The herd or flock must remain closed to avoid reintroduction of disease. Often, 3 to 5 negative annual tests are required before the herd or flock can be called low risk of disease. There is currently no national or provincial program for certifying herds or flocks free of Johne's disease.

References