If you’re an experienced bear hunter, you’ve no doubt heard about the perils of Trichinosis, a parasitic infection associated with eating undercooked pork or bear meat. A century ago, nearly everyone would have been familiar with this risk, but modern agricultural practices have virtually eliminated it in commercial pork production. Human cases in North America are now largely associated with wildlife, and general awareness is low. As a result, Trichinosis prevention may be a topic that hunters only encounter when and if they start predator hunting. It’s a lesson well worth learning but preferably not from personal experience. 

While general awareness wanes, a surprisingly popular cautionary tale for Trichinosis has emerged in the outdoor media. I’ve even heard it referenced among friends as ‘you know, that thing Steve Rinella got.’ And it’s true. Rinella, host of the popular MeatEater podcast, talks openly about his personal experience with Trichinosis. Whether intended or not, his story has probably raised more awareness among hunters than legions of scientists ever could. I was curious how Rinella felt being the public face of a rare parasitic infection, but when I asked him recently, he just laughed about the somewhat dubious honor.  

As the story goes, Rinella was hunting black bears with a group in Alaska in 2014. After a successful harvest, they attempted to cook fresh bear meat over a campfire. Damp weather prevented the fire from getting hot, and the group was pressed for time. Admittedly complacent about the risk, Rinella said they even joked about getting Trichinosis as they ate the undercooked meat. Weeks later, and scattered across the U.S., the group experienced a pattern of stomach issues, fever, and muscle pain. Fortunately, Rinella was put in touch with the state epidemiologist for Alaska who immediately recognized the issue and helped guide them toward answers. Unnerving as it was, everyone recovered, and the group commemorated the experience with matching t-shirts. I think Rinella’s story highlights some key points as we talk about Trichinosis. 

Trichinosis (also known as Trichinellosis) is a general term for infections involving worms from the genus Trichinella. While Trichinella spiralis is most often discussed, a recent scientific review in the International Journal for Parasitology: Parasites and Wildlife highlights that there are actually 13 distinct types of Trichinella reported in wildlife from every continent except Antarctica, but that is likely the tip of the iceberg for the number of species that may exist. Of the 13 species described, Trichinella spiralis is the only one that occurs worldwide. Five additional species have been documented in North America, one in South America, three in Europe, five in Asia, and four in Africa, with some species occurring on multiple continents. Nine of the 13 species are known to infect humans, but many cases are not diagnosed amongst species. Trichinella spiralis and Trichinella britovi are the most common causes of Trichinosis in Europe where the disease is associated with farmyard pigs and wild boar. In North America, Trichinella spiralis and Trichinella nativa are common culprits, and their occurrence is almost exclusively linked to wildlife and increases with latitude. 

The scientific review cites evidence that the detection of Trichinosis in human populations is 800 times greater in northern Nunavut, Nunavik and Quebec than elsewhere in Canada. Similarly, the annual incidence of human Trichinosis in Alaska is 40 times higher than in the rest of the U.S. This increased occurrence of Trichinosis at the higher latitudes can be attributed to several things. First, at least four species of Trichinella overlap in parts of northern Canada, Alaska, and Greenland. Additionally, species like black bear, polar bear, walrus, and seal are more prevalent and more frequently used by residents in this region. With increased exposure risk also comes increased awareness, better surveillance, and more accurate diagnoses. One important characteristic of the Trichinella species adapted to these northern climates is their cold tolerance. While Trichinella spiralis and other species are inactivated by prolonged freezing, Trichinella nativa is one of at least four species that easily survive freezing temperatures. 

Despite their differences, Trichinella species tend to share a similar life cycle, and that cycle is somewhat unusual because it occurs in a single host (most parasites use different hosts for each life stage). As juveniles, Trichinella larvae make themselves comfortable in the muscle tissues of their host where they can persist for months to years. When infected meat is eaten, digestion releases the larvae into the new host. They mature to adulthood and reproduce in the lining of the small intestine. New juveniles emerge and enter nearby lymph and blood vessels, which distribute them to muscles throughout the body. Once distributed, the new generation of larvae settles in and will become infectious for another host within weeks. Understanding this cycle, it’s easy to predict that predation, cannibalism, and scavenging are effective routes of transmission, making carnivores and omnivores the most likely hosts. Common hosts include rats, foxes, raccoons, wild boar/feral pigs, bears, wild cats, and marine mammals. Humans are considered a dead-end host for this parasite, meaning they can become infected but do not contribute to further transmission. 

The symptoms of Trichinosis reflect the parasites’ life cycle. The reproductive phase can cause abdominal pain, diarrhea, and vomiting. Larval migration to muscle tissue is associated with muscle pain, facial swelling, fever, and rash. Symptoms often resolve on their own, but treatments are sometimes offered. Although extremely rare, the infection can become life threatening if it involves the heart, central nervous system, or lungs. Unfortunately, the symptoms of Trichinosis are similar to other ailments and medical professionals may not be familiar with this parasite, especially in areas where it is uncommon. It’s not surprising that a public health official from Alaska was able to diagnose Rinella’s team when others couldn’t. It highlights how important it is for hunters to be well-informed so they can have the right conversations with their doctors. 

Although the risk of Trichinosis is real, it’s also easily prevented. The standard recommendation to prevent infection is to cook game meat to an internal temperature of 160°F (71°C), confirm the temperature with a thermometer, and allow the meat to rest for three minutes before cutting. While freezing is sometimes recommended for pork, Trichinella species in wildlife can be resistant to this method as we’ve discussed. Additionally, these exceptionally sturdy parasites are not inactivated by food preparations like curing, smoking, pickling, fermentation, dehydration, or microwave cooking. Though Trichinosis may be more common in the far north, it can occur anywhere, and it’s wise to treat all bears with equal caution. While we’re on the subject, let’s not forget man’s best friend. Trichinella parasites can infect almost any mammal, so feeding uncooked scraps to pets can put them at risk of infection. 

There’s no doubt that hunters like to try new things. Whether it’s a deer hunter pursuing bears for the first time or a seasoned bear hunter heading north for a new experience, trying new things is part of the adventure. While new experiences can bring new risks, plenty of information is available to help hunters prepare. In the case of Trichinosis, prevention is so easy that Rinella even told me, “If you get sick, you’re asking for it.” He would know. 

References 

Malone, C.J., Oksansen, A., Mukaratirwa, S., Sharma R., Jenkins, E., 2024. From wildlife to humans: the global distribution of Trichinella species and genotypes in wildlife and wildlife-associated human trichinellosis. Int. J. Parasitol. Parasites Wildl. 24, 100934. 

https://www.mayoclinic.org/diseases-conditions/trichinosis/symptoms-causes/syc-20378583 [accessed May 1, 2024]