Paratuberculosis

Paratuberculosis is a contagious and fatal disease that mainly affects domestic ruminants, such as sheep, cattle and goats. It is also known as Johne’s disease. Paratuberculosis is caused by the Mycobacterium avium ssp. Paratuberculosis bacterium, which affects the small intestine and causes lesions. These lesions are detrimental to the normal absorption process.

The most commonly infected animals are domestic ruminants, such as cattle, sheep and goats, as well as wild ruminants.

Infected animals do not have a fever or appetite loss. The clinical signs are:

• Diarrhea, intermittent at first, then chronic
• Progressive weight loss
• Weakness
• Decrease in milk production

The prevalence of clinical signs varies depending on the species: Cattle frequently have diarrhea, while goats and sheep rarely do.

In a herd, the disease can lead to a higher mortality rate. Milk production can decrease. The disease can also cause reduced feed conversion efficiency, premature culling, reduced growth and reduced slaughter values. The disease generally leads to significant financial losses for producers.

Animals are most often infected by ingesting the bacteria. Since the bacteria multiply in the small intestine, it is found in excrement. This is also the case for animals that do not show any symptoms. The bacteria thus contaminate food and the environment. 

The  colostrum ^{Read the content of the note 1} and the milk of a contaminated animal are also potential sources of infection. As the disease progresses, the number of bacteria in milk and excrement increases.

Fetuses can also be contaminated (in utero), especially when the mother shows signs of the disease.

The bacterium’s  incubation period ^{Read the content of the note 2} varies between two and six years.  Animals that develop the disease are often over the age of five, but were infected early in life, before the age of nine months. As they age, animals show a certain resistance to infection.

The long period of time during which an infected animal shows no symptoms of the disease puts the entire herd at risk. Even if the animal is not visibly ill, it will still excrete the bacteria. The bacteria can survive, but not multiply, for several months in the environment. The bacteria are resistant to the cold, hear and disinfection. 

As a result, purchasing an animal that excretes bacteria without showing signs of the disease could infect the entire herd. Sharing materials and grassland contaminated with infected animal manure can also infect animals from other herds.

Paratuberculosis is a chronic disease that must be considered both a herd and an individual problem. There is no treatment for this disease.

No vaccine can effectively prevent an animal’s infection.

Several measures can help prevent this disease in animals and transmission to humans. These measures help decrease the number of infected animals.

There are major advantages to culling infected animals and not trying to keep them in the herd, as they play a significant role in transmitting the bacteria.

We recommend that you talk to a veterinarian about your herd’s risk factors. You should implement measures to control these factors and follow the disease’s evolution if it is detected on your farm. Also ensure rigorous monitoring and constantly apply best management practices. 

Detecting the disease

Necropsy should be the preferred approach to confirm the disease in an animal that shows clinical signs. However, a diagnosis is more difficult before signs appear.

Two screening tests can be useful. It is possible to try to detect the bacterium through a manure or milk sample, or to check for antibodies in an animal’s blood or milk.