Todayโs path rounds are on the ๐ฉ๐จ๐ซ๐ค ๐ฐ๐จ๐ซ๐ฆ, ๐๐ซ๐ข๐๐ก๐ข๐ง๐๐ฅ๐ฅ๐ ๐ฌ๐ฉ๐ข๐ซ๐๐ฅ๐ข๐ฌ!
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
๐๐ซ๐ข๐๐ก๐ข๐ง๐๐ฅ๐ฅ๐ ๐ฌ๐ฉ๐ข๐ซ๐๐ฅ๐ข๐ฌ is a roundworm whose larvae like to live in muscle tissue, while the adults live in the small intestine. They have been known to cause outbreaks of disease in humans, because they are ๐ณ๐จ๐จ๐ง๐จ๐ญ๐ข๐ (infect both humans and animals)!
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
Pretty much any species can get this, but we classically think of it in pigs. In fact, this roundworm is the main reason that you should never eat undercooked pork!
๐๐ก๐๐ญ ๐๐๐ฎ๐ฌ๐๐ฌ ๐ข๐ญ?
As mentioned, the adults of this parasite live in the small intestine of pigs, where they burrow into the intestinal wall and invade the lymphatic vessels. They deposit their larvae into the lymphatics, and from there the larvae flow through the lymph into the bloodstream to enter general circulation. Then, they seek out muscle tissue to burrow into and form a little house for themselves. The larvae can live in these cysts for up to 20 years, just waiting for something to come along and eat its hostโs muscle tissue, so it can be transmitted to another animal.
๐๐ก๐ฒ ๐ข๐ฌ ๐ญ๐ก๐ข๐ฌ ๐ ๐ฉ๐ซ๐จ๐๐ฅ๐๐ฆ?
The infection of a muscle with large numbers of larvae can cause muscle weakness and paralysis of the muscle, leading to consequences depending on what that muscle is used for. Typically, the muscles most commonly affected in this disease are the tongue and diaphragm, so severely affected animals may have difficulty eating or breathing. However, the vast majority of animals will be ๐๐ฌ๐ฒ๐ฆ๐ฉ๐ญ๐จ๐ฆ๐๐ญ๐ข๐ (no symptoms), so you may have no idea that they are infected!
๐๐ฎ๐ญ ๐ฐ๐ก๐๐ญ ๐๐๐จ๐ฎ๐ญ ๐ก๐ฎ๐ฆ๐๐ง๐ฌ?
Interestingly, humans can actually get some symptoms from ingesting contaminated meat! Humans can experience diarrhea, vomiting, abdominal pain, muscle pain, weakness, fever and swelling. In severe infections, people may even have heart and breathing problems, and occasionally may die from infection.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
Typically this disease is best diagnosed by examining a muscle biopsy under a microscope to visualize the larvae directly. However, meat inspectors are sometimes able to diagnose it at the time of slaughter by looking at the muscle for little white dit dots, which form when the encysted larvae die off and ๐๐๐ฅ๐๐ข๐๐ฒ (become coated in calcium).
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐? ๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ฉ๐ซ๐๐ฏ๐๐ง๐ญ๐๐?
Treatment is generally not practical, so prevention is key for this disease. The best means of prevention for pigs are controlling rodent access to farms, cooking meat products fed to the pigs, and preventing tail biting or other cannibalistic behaviours. For people, making sure that your pork is cooked to an adequate temperature is the best method of prevention, as doing so will kill the larvae.
๐ ๐ฎ๐ง ๐๐๐๐ญ: Many countries have gotten so good at controlling Trichinella spiralis that the food safety agencies have been able to reduce the minimum temperature for cooking pork, because we rarely see this disease now! Cool.
๐๐ก๐จ๐ญ๐จ๐ฌ
1-2) Examples of the larvae before they encyst themselves in the muscle.
3-5) Examples of what a pathologist would see on a muscle section under a microscope! Little larvae in their little larvae homes 
6) An example of a muscle with lots of calcified larvae in it. This tissue is from a bear 
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Maxie, G. Jubb, Kennedy and Palmerโs Pathology of Domestic Animals, Volume 1. Sixth Edition.
Pozio, E. Trichinellosis in Animals. Merck Vet Manual 2021.
Photos 1-7 ยฉ Noahโs Arkive contributors McGavin, Qualls, Jakowski, Lezama, Prestwood, King licensed under CC BY-SA 4.0.
