By Sarah A. Orlofske, University of Wisconsin – Stevens Point
This article originally appeared in Wisconsin Waterfowl Association’s September Newsletter edition.
When I talk to waterfowl hunters and share that my research involves studying waterfowl parasites, the most common parasite they ask about is Rice Breast. The common name provides an accurate description of the protozoan parasite known scientifically as Sarcocystis spp. It is a frustrating parasite for hunters since the birds are unlikely to show any evidence of infection prior to being harvested. However, after the bird has been skinned the parasite is readily identified by the small, white cylinders, looking like grains of rice, mottled among the breast muscle fibers. The white “cysts” are the larval stage of the single-celled parasite using the bird as a means of transmission to the final host in the two-host life cycle. The final host is typically a carnivorous mammal like a coyote or fox that becomes infected by consuming the infected bird. While it makes sense that these species interact as predator-prey and that parasites could exploit that relationship for their own transmission, the life cycle wasn’t uncovered until the late 1970s.
Close up of Rice Breast from a Blue-winged Teal. Photo from Todd Huspeni.
It may also seem surprising that this parasite is an apicomplexan, putting it in the same taxonomic group as important human pathogens like Plasmodium spp. parasites that cause Malaria and Toxoplasma gondii responsible for human birth defects in pregnant women. The life cycle is very different from Malaria, which is carried by mosquitoes, but very similar to T. gondii which also has a life cycle dependent on predator-prey relationships but this one typically between mice and cats.
You might be thinking about all this consumption and wonder, can humans consume waterfowl infected with Rice Breast? While it may look unappetizing, if the meat is properly cooked it would be safe for human consumption. If not properly cooked humans could end up as accidental, dead-end hosts for the parasite, which could result in non-specific symptoms like nausea and diarrhea. Humans are not the proper host for the species of Sarcocystis found in waterfowl, but can serve as hosts for other species of the parasite that are transmitted through livestock like cattle and pigs. It is important to remember that the meat can be consumed if handled and cooked properly so that the meat doesn’t go to waste unnecessarily. However, if you have an extremely infected bird and don’t plan to eat it you should still take it home and dispose of it properly rather than leave it for predators that would perpetuate the lifecycle and don’t feed it to pets like dogs or cats. Although it is unlikely these domestic animals could host the parasite, dogs do serve as host for other species of Sarcocystis so it is important to be careful.
Rice Breast is hard to avoid at harvest because it doesn’t cause significant pathology to waterfowl unless at extremely high infections. The parasite has been recorded from many species of waterfowl throughout the United States, but dabblers like mallards and teal tend to be more infected than divers because of their feeding habits. Waterfowl become infected by consuming the infective stage of the parasite as they forage in aquatic environments. The good news is that, while the parasite would be difficult to manage, it is unlikely to cause harm to waterfowl populations.
References:
Foundations of Parasitology, 9th Ed. Roberts & Janovy
Rolfe, T.J. and Craven, S. Rice Breast Disease In Waterfowl A publication of the U.S. Fish and Wildlife Service.