Johne's disease

Description

Johne’s disease (paratuberculosis) is a chronic debilitating disease that affects the intestines of all ruminants, including cattle, sheep and goats. This disease is caused by Mycobacterium Avium Subspecies Paratuberculosis (MAP), which is closely related to the organisms that cause tuberculosis and leprosy.

Although many animals in a herd may be infected, usually less than 5% of those infected develop clinical signs of disease. This is called the ‘iceberg effect.’ Under stress, inadequate nutrition or parasitism, a larger percentage of the herd may develop clinical signs of Johne’s. Once clinical disease develops, affected animals eventually die due to dehydration and starvation as a result of malabsorption of nutrients. There is no treatment for Johne’s disease.

There is no practical diagnostic test that reliably detects Johne’s disease (JD) in asymptomatic animals. The fact that MAP grows very slowly delays the immunological response and detection of the bacterium in serum and in feces.

The epidemiology of the disease is different in dairy and beef herds, mainly due to management factors. It is estimated that approximately 50% of Alberta dairy herds and 15% of beef herds may be infected with MAP. However, these numbers may be higher due to the factors explained above.

The most significant economic losses associated with JD are decreased milk production and reduced salvage value of clinically affected animals. Affected animals have an increased risk of being culled early and have lower slaughter weight.

Johne’s disease is a provincially notifiable disease for cattle and yaks, sheep and goats, domestic cervids and farmed bison.

How to report

Johne’s disease is a provincially notifiable disease under Alberta's Animal Health Act and must be monitored. All suspected or confirmed cases must be reported to the Office of the Chief Provincial Veterinarian (OCPV) within 24 hours:

Hours: 8:15 am to 4:30 pm (open Monday to Friday, closed statutory holidays)

Phone: 780-427-3448
Toll free: 310-0000 before the phone number (in Alberta)
Fax: 780-415-0810

How it spreads

MAP does not cause disease in non-ruminant animals such as horses and pigs. However, these animals may perform as reservoirs, creating a risk to transmit the disease.

Calves under 6 months of age are the most susceptible to infection. Infection with MAP is usually acquired by consuming feed and water contaminated with manure from infected animals. MAP may also be shed in milk and some calves from cows under advanced clinical disease may be born infected.

Less than 5% of infected animals develop clinical signs of illness. The reason for this is unknown. Infected animals without clinical signs act as carrier animals and are a source of contamination on the farm.

MAP is resistant to environmental degradation, as well as many disinfectants. This organism survives in stagnant water, manure or deep soil for up to a year. It also withstands freezing at minus 14°C for up to a year. The ability of this organism to survive in the environment is reduced by the presence of urine or by the ensiling process.

Clinical signs

Clinical signs of disease are rarely observed in animals under 2 or 3 years of age. However, calves exposed to a heavy burden of MAP may show clinical signs at 18 months of age. Affected animals may develop intermittent bouts of diarrhea that gradually become more frequent. As a result of the chronic protein loss through diarrhea, affected animals may develop ventral edema (bottle jaw). Other animals suddenly develop diarrhea, which persists until death.

Progressive weight loss is typical of this disease and may begin before diarrhea develops. Although affected animals appear unthrifty, with a rough hair coat and declining milk production, their appetite remains normal until the terminal stages of the disease.

Weight loss without diarrhea is the main sign of disease in sheep and goats.

Diagnosis

There is no practical diagnostic test that reliably detects infections by MAP in asymptomatic animals. Culture of feces for MAP is expensive because of the long time required to grow the organism. Cultures must be incubated for up to 4 months before they can be called negative.

Intermittent shedding also makes a negative fecal culture difficult to interpret. Several blood tests are available but the number of false positives and negatives makes these tests unreliable.

Animals with chronic, non-responsive diarrhea and progressive emaciation, coupled with a normal appetite, should be considered as JD suspects. Producers should contact their veterinarians at this stage.

Johne’s disease is confirmed by a postmortem examination where increased thickness and transverse folds in the intestinal lining are observed.

Prevention and control

Currently, no Johne's disease vaccines are licensed for use in Canada.

An effective biosecurity plan is essential to prevent the introduction of infectious diseases like JD into a herd. Continuous evaluation of biosecurity procedures is important. Commitment, dedication and persistence by all farm staff including owners and visitors is required for successful implementation of biosecurity.

To reduce the risk of introducing JD into a herd, producers should rear their own replacement heifers. Purchasing replacements from herds of unknown health status is risky because of the lack of a reliable test to detect infected animals that are not showing clinical disease.

Once herds are infected

Infected herds may have up to 20 times more carrier animals than those showing signs of disease. Because of the difficulty in detecting carrier animals, eradicating JD from a herd is rarely successful. Even complete depopulation may be unsuccessful due to the risk of purchasing carrier animals to repopulate the herd. Rigid culling procedures and improved herd management will reduce JD to acceptable levels.

Recommended management practices for infected herds include:

• Cull animals exhibiting signs of clinical disease that suggest JD. Have the carcasses examined to confirm the diagnosis.
• Separate unthrifty animals from the herd.
• Clean and disinfect areas where affected animals have been kept. MAP is susceptible to 10 minutes exposure to 5% formalin, 1:32 cresylic disinfectant, 1:40 phenol, 1:1000 mercury bichloride and 1:50 calcium hypochloride.
• Remove manure from the barnyard regularly and avoid spreading manure on pastures.
• Pasture calves on clean pasture and maintain in winter quarters separate from adults until the heifer enters the milking herd.
• Drain, fill or fence off sloughs.
• Prevent contact of young animals with adult manure drainage.
• Prevent feed and water contamination with manure. Drinking water should be piped from clean sources.
• Remove calves from their dams immediately after birth and put them in clean quarters separate from adult animals.
• Clean the udder before drawing colostrum for calf feeding.
• Only feed pasteurized colostrum and pasteurized milk. If necessary, switch to a high-quality powdered milk replacer after 72 hours of age.
• Once the disease has been diagnosed in a herd, avoid selling the animals for dairy or breeding purposes.

Government actions

The Canadian Johne’s Disease Initiative (CJDI) ran from 2006 to 2013. Producer initiated and industry led, the program was created to promote awareness and education on JD, and reduce the prevalence of this disease in Canadian herds. CJDI laid the framework for today’s livestock industry’s biosecurity-based, preventive approach to disease control.

Find out more about the initiative:

• Canadian Johne’s Disease Initiative: Dairy Cattle
• Biosecurity for Canadian dairy farms: National standard
• Lessons Learned from the Canadian Johne's Disease Programs

JD is a provincially notifiable animal disease in Alberta. The disease does not require government action but is monitored to establish prevalence or trends. Between 50 and 100 cases of Johne’s Disease are confirmed in Alberta each year. See confirmed cases of regulated animal diseases in Alberta.