Heterophyes heterophyes

Heterophyes heterophyes is a parasitic fluke that can infect humans that is classified within the Trematoda class. Its range is large and includes China, North Africa, Korea, Japan, Asia Minor, the Philippines, and Taiwan. Adults reach an average size between .03 inches and .06 inches. Its body is covered with scales, occurring in higher numbers near the front end, which holds an oral sucker. There is an acetabulum located near the middle of its body and two testes on the back end. The female fluke of this species has a different anatomy than males, with an ovary located near the end of the body. However, both sexes’ reproductive organs lead away from the back end of the body to the ejaculatory duct. In females, this duct leads to a genital sinus and then to a genital pore, where females can release eggs.

Adult heterophyes heterophyes flukes live in the intestinal villi of its host. Eggs are laid underwater and have a miracidium. These eggs will not hatch until they have entered a species of snail, like Cerithidia cingula in Japan and Pirenella conica in Egypt. Once the eggs are inside of a snail, the miracidium of each egg turns into a sporocyst that is able to produce rediae, which then produce a type of larvae known as cercariae. These larvae swim to the surface of the water and slowly sink back down, eventually landing on a fish. Once the larvae have pushed through the epithelium of the fish, they are able to move into the muscle tissue. In these stages of its life, the larvae are living in intermediate hosts, but once infected raw fish is consumed, they are able to move into definitive hosts like birds and humans.

Humans that live near bodies of water within the range of heterophyes heterophyes are more likely to contract this species than those who do not, and fisherman are at highest risk. Because raw fish comprises such a large portion of people’s diet in the flukes range, people living in areas with higher numbers of the species are especially more at risk.

Symptoms of an infection include intestinal pain, mucosa diarrhea, and inflammatory reactions in the area where the parasite entered the intestine. Eggs can occasionally leave the intestines and move through the lymph vascular systems and blood of their host. These eggs can enter the heart and brain of the host, causing neurological disorders, heart failure, and death. It can be difficult to diagnose an infection of this species if adult individuals are not present in a stool sample, because the eggs are too similar to C.sinensis eggs to distinguish between the two species. Treatments include the medicine Praziquantel, which is a derivative of quinolone.

Image Caption: An adult of Heterophyes heterophyes (Trematoda: Opisthorchiida: Heterophyidae) stained with carmine. OS – oral sucker, PH – pharynx, IN – intestine, AC – ventral sucker or acetabulum, UT – uterus with eggs. Credit: Division of Parasitic Diseases and Malaria / Wikipedia