Johne's Disease (Paratuberculosis)
What is it?
A disease found around the world and caused by bacteria, (Mycobacterium avium subspecies paratuberculosis) which affects ruminants’ intestines. Animals like cattle, goats and sheep are among the most commonly infected with the disease. The USDA’s Animal and Plant Health Inspection Service offers a nationwide voluntary control program to slow and stop the spread of the disease among America’s livestock. According to the World Organisation for Animal Health, Johne’s is named for the veterinarian who first identified the organism in 1894.
How is it transmitted?
The bacteria is shed from infected animals in their manure and milk. Young animals are at the highest risk for becoming infected and can often be born with the disease or contract it when nursing, either through milk or through ingesting manure contaminating the udder. Infected adult animals can carry the disease with minimal clinical signs, and shed it in their manure to infect healthy herds.
What are the clinical signs?
The absence of clinical signs is what makes this disease hard to identify. Infected animals can live for years with the disease without any obvious outward indications. Young livestock are unlikely to develop clinical signs until they are at least two years of age because of its slow progression.
When clinical signs do appear, they include weight loss, diarrhea and low milk production.
How is it diagnosed?
It’s possible to test for Johne’s using serum, milk or fecal samples. Screening tests can be used to determine whether the disease exists in a herd. An ELISA test on milk or serum can be used as a screening test. Positive test results can be confirmed using official tests such as fecal culture or PCR. Negative fecal results are not always reliable, because some infected animals irregularly shed the disease, or not at all. A necropsy of a dead animal can identify Johne’s in the intestine, and confirm it via histopathology, or microscopic examination of the tissue.
Is there a risk to people?
Some studies have suggested the M. Avium ssp. paratuberculosis bacterium is involved in Crohn’s disease in humans. However, there is not a concrete link between the two, and it has not been demonstrated to transmit between animals and people.
How can it be prevented?
There is no known cure for Johne’s. Various treatments have been attempted which may offer some improvement and prolong life, but the disease is ultimately fatal. The USDA’s Johne’s Disease Control Program is focused on preventing the spread of the disease through education, herd management, test and removal procedures. This program suggests herd owners gain a Johne’s free herd status by conducting routine testing. Once the herd has achieved a negative status, the owner should only introduce animals into the herd from other test-negative herds.
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