Todayโs path rounds are on ๐๐จ๐ก๐ง๐โ๐ฌ ๐๐ข๐ฌ๐๐๐ฌ๐, otherwise known as paratuberculosis!
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
๐๐จ๐ก๐ง๐โ๐ฌ ๐๐ข๐ฌ๐๐๐ฌ๐ is a bacterial disease of ruminants that primarily affects the intestinal tract. It is a huge source of production loss, particularly for dairy cattle, so it is a very important disease!
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
This disease is most common in domestic ruminants, like sheep, cattle and goats. However, it can also occur in other species. Interestingly, it only seems to affect older animals, due to a long ๐ฌ๐ฎ๐๐๐ฅ๐ข๐ง๐ข๐๐๐ฅ ๐ฉ๐๐ซ๐ข๐จ๐ where the animal shows no clinical signs, despite being infected.
๐๐ก๐๐ญ ๐๐๐ฎ๐ฌ๐๐ฌ ๐ข๐ญ?
Johneโs is caused by ๐๐ฒ๐๐จ๐๐๐๐ญ๐๐ซ๐ข๐ฎ๐ฆ ๐๐ฏ๐ข๐ฎ๐ฆ ๐ฉ๐๐ซ๐๐ญ๐ฎ๐๐๐ซ๐๐ฎ๐ฅ๐จ๐ฌ๐ข๐ฌ (MAP). This bacteria is primarily transmitted through fecal contamination of feed, but can also be transmitted in milk or water.
Once in the intestinal tract, the bacteria invades the cells lining the small intestine, and is taken up by ๐ฆ๐๐๐ซ๐จ๐ฉ๐ก๐๐ ๐๐ฌ (the bodyโs main clean-up cell) into a ๐ฉ๐ก๐๐ ๐จ๐ฌ๐จ๐ฆ๐ (a storage bag within a macrophage). Normally, things ingested by macrophages are broken down quickly by ๐ฅ๐ฒ๐ฌ๐จ๐ฌ๐จ๐ฆ๐๐ฌ (big bags of enzymes that fuse with the phagosome). However, MAP is able to prevent fusion of lysosomes to phagosomes, allowing it to survive within the macrophage.
The bacteria will live happily in these macrophages for up to 2-5 years, with the animal constantly shedding low levels of bacteria in the feces that can infect other animals. After a long period of time, the bodyโs immune system finally takes notice, and begins a rapid, but not very effective, immune response against the bacteria, leading to clinical signs for the affected animal.
๐๐ก๐ฒ ๐ข๐ฌ ๐ญ๐ก๐ข๐ฌ ๐ ๐ฉ๐ซ๐จ๐๐ฅ๐๐ฆ?
Once the immune system has kicked in, a ๐ ๐ซ๐๐ง๐ฎ๐ฅ๐จ๐ฆ๐๐ญ๐จ๐ฎ๐ฌ ๐ซ๐๐ฌ๐ฉ๐จ๐ง๐ฌ๐, accumulation of large numbers of macrophages, occurs in the intestine and nearby lymph nodes. This accumulation leads to thickening of the intestinal mucosa, which prevents proper absorption of nutrients and water from the intestinal tract. As a result, these animals develop diarrhea and severe weight loss, because they canโt get any of the nutrients they need to survive. Eventually these animals will die.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
Usually this disease is diagnosed based on clinical suspicion, as it is one of the main causes of diarrhea and weight loss in an older ruminant. However, if a clinician wants to confirm their diagnosis, they can run a culture or PCR test on the feces to detect the bacteria. At necropsy, the classic lesion is thickening of the intestinal mucosa, which produces thick folds along the inner intestinal surface. Often, you can also see ๐ฅ๐ฒ๐ฆ๐ฉ๐ก๐๐ง๐ ๐ข๐ญ๐ข๐ฌ (swelling of the lymphatics) in the lymph vessels of the ๐ฆ๐๐ฌ๐๐ง๐ญ๐๐ซ๐ฒ (the connective tissue that holds the intestines together).
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐?
Unfortunately, there is no treatment for clinical Johneโs disease. Prevention is the key to management. Animals should be tested before being introduced to a herd, and young animals should be kept in clean environments with minimal exposure to older animals.
๐๐ก๐จ๐ญ๐จ๐ฌ
1) A segment of thickened intestine due to Johneโs disease.
2) The classic appearance of thickened intestinal mucosa forming folds.
3) Dilated lymphatics due to Johneโs disease.
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Maxie, G. Jubb, Kennedy and Palmerโs Pathology of Domestic Animals, Volume 2. Sixth Edition.
Photos 1-3 courtesy of University of Calgary Diagnostic Services Unit.
