Johne’s Disease, which is caused by Mycobacterium avium paratuberculosis (MAP), is not just a disease that’s potentially devastating for the cattle, sheep, and goats that contract it. It can be a costly nightmare for farmers and may even have health impacts on humans.
In the NSH webinar, Jonesing For Johne’s - AFB Control Tissue, presenters Kathryn Stoll, AS, HT (ASCP)CM of Newcomer Supply and Tori Smith, HT (ASCP)CM of Wisconsin Veterinary Diagnostic Laboratory give us a comprehensive look at the various effects of Johne’s Disease, as well as how histotechnologists use their expertise to confirm it.
The Toll Johne’s Disease Can Take
Since Johne’s Disease is highly contagious and has no cure, when a ruminant develops the condition, it can often lead to culling an entire herd. It’s also a tricky condition because animals may be asymptomatic if they contract the disease in utero, so tests may not detect that there’s anything wrong.
Stoll explains how the disease progresses in cows this way: “In the early phase—birth to six months—the animal is infected, but not at all showing signs of symptoms. It will rarely test positive, and it’s not shedding the bacteria to other animals at this point. In the two- to six-year phases, the shedding of the bacteria is at really low levels. The animal might appear healthy, and then eventually we’ll start to have a little bit of the symptoms of Johne’s. This is where the infection is starting to spread slowly through the intestinal tissue and the associated lymph nodes. In the clinical phase, the animal is very sick. We’re seeing diarrhea and weight loss. It's affected the whole immune system at this point. The MAP antigens are activating the T cells, and then these granulomas are going to form in the intestines, and this is where you’re really going to see all of the symptoms and the high shedding.”
You’re also going to see astronomical expenditures. According to the U.S. Department of Agriculture, each year Johne’s Disease costs dairy farms $200 million in veterinary bills, testing, and reduced production. In addition, these sick cows need to be removed from the herd, which means additional losses for the farm. If the animals are sold for feed, the farmer loses a significant amount of money—$350 per cow compared to the $2,700 that’s charged for a healthy one. In other cases, farms will pay out of pocket to have the cows taken from the herd.
Human Exposure to MAP
You can take a MAP-infected cow out of the herd, but you can’t take the bacteria out of the milk. In fact, despite the effectiveness of pasteurization in killing most bacteria, 2% of milk that undergoes this process still has live MAP in it. Similarly, chlorinated water has been shown to have the bacteria in it because it’s resistant to disinfection. MAP can also be found in raw cheeses and ground beef.
Thankfully, MAP is not communicable in humans as it is in cows. However, that doesn’t mean exposure has no human cost. While the link is not definitive, there is a connection between MAP and Crohn’s disease, as well as multiple sclerosis.
With so much at stake for humans and animals, the work of histotechnologists to diagnose MAP is a high-stakes affair. To find out how to perform a necropsy on cow intestines, engage in MAP surveillance, and recognize MAP grossly and histopathologically, watch the NSH Jonesing For Johne’s - AFB Control Tissue webinar.
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