By Tasiujaq Mayor Billy Cain, Géraldine-G Gouin, Wildlife Disease Specialist, Nunavik Research Centre, and Adrián Hernández Ortiz, Department of Veterinary Microbiology, University of Saskatchewan
In the fall of 2019, Tasiujaq Mayor Billy Cain noticed unusual tiny white spots in some caribou meat. He had never seen this before. The spots (which turned out to be parasitic cysts) looked like grains of rice (see figure 1). Of the 12 caribou that he had hunted, only one had these cysts and the animal seemed fine otherwise. In the winter, and later on in the spring, Billy noticed the same type of cysts in some more caribou; in total he found seven infected animals. Because he had noticed it more than once (and he suspected that it was a parasite), he decided to send a sample of meat from the winter hunt to the Nunavik Research Centre (NRC).
The NRC team examined the sample and found that the cysts resembled a parasitic genus called Sarcocystis spp. This is a type of protozoan (a very small parasite), which has a characteristic “grain of rice” appearance. Sarcocystis spp. is a common parasite that is found in many species, notably mammals and birds. The vast majority of them are harmless to humans.
To validate the theory that the spots found by Billy in his caribou meat were in fact Sarcocystis spp., the NRC team isolated one parasite from the meat and looked at it under the microscope. The cyst, called a sarcocyst (see figure 2), contains a high number of small crescent shaped cells. These cells are what causes infection when the meat is eaten by another animal. When the NRC team looked at the cyst under the microscope and applied soft pressure many crescent shape cells were indeed squeezed out.
The life cycle of Sarcocystis spp. is simple and includes two animal hosts: one definitive host like a wolf or a lynx and one intermediate host like a caribou. The intermediate host gets infected when it eats eggs found in the feces of the definitive host. Then, the parasites migrate to the muscles of the intermediate host, where it encysts. Until the animal is eaten by the definitive host, the parasite will stay in the intermediate host muscles. For example, if an infected wolf poops in the tundra, some tiny parasitic eggs will be left on the surface of lichen, rocks, willows, etc. Those eggs can then be eaten by a caribou, who then becomes infected with Sarcocystis spp (see figure 3).
Reindeer are the intermediate host for some Sarcocystis species that have been identified in Europe. Sarcocystis cysts in reindeer have been found in different muscles including the heart, esophagus, diaphragm, and skeletal muscles. The size of the cysts vary from 1 mm to 16 mm long, depending on the species. Sarcocystis species in caribou in North America are still being studied. In fact, the few existing reports of Sarcocystis spp. in caribou in Canada only describe the appearance of Sarcocystis spp. without describing them in detail. In this case, we used an advanced method to figure out which species of Sarcocystis infected the caribou found by Billy.
In order to do this, the samples were sent to University of Saskatoon where DNA was extracted from different sections of muscle tissue from the caribou meat. Samples were then tested using molecular techniques that allowed for the detection of small parasites called coccidians (like Sarcocystis spp.). After getting the results, samples were sent for sequencing, a technique that allows researchers to identify organisms with more certainty. The sequencing results identified the parasite as Sarcocystis rangiferi.
The pathogenicity (ability of an organism to cause disease) of Sarcocystis spp. infections in reindeer has not been studied. It is likely that one or more species contribute, along with other parasites, to reduced health and growth of reindeer.
Risks to human health caused by eating caribou infected with Sarcocystis rangiferi seem unlikely. There are currently a very low number of Sarcocystis spp. in the world that can infect humans when they eat raw meat, and so far, Sarcocystis rangiferi is not one of them. However, not many studies have been conducted on the transmissibility of caribou’s sarcocyst to humans. If ever it was transmissible, most people will show no symptoms at all. However, in rare cases it can cause slight fever, diarrhea, vomiting and mild respiratory problems. If you are not sure about what to do with infected caribou meat, you can cook it up to 71° C or freeze the meat to -4° C for 48 hours to kill the parasite. Don’t feed raw infected caribou meat to your dogs as they could get contaminated!
This is the first time that Sarcocystis rangiferi has been identified in North America. The impact on caribou health, the number of infected caribou and the severity of infestations remains unknown and needs to be further studied.
If ever you see parasite cysts that look like the ones in the picture, please sample (cut out) a small part of the infected meat and/or use your cellphone to take a picture. Send the sample and/or picture to the Nunavik Research Centre by calling 819-964-2925.