Heterophyes Infection (Heterophyiasis)

Heterophyiasis is an infectious disease caused by the trematode known as Heterophyes heterophyes, a very small intestinal flatworm or fluke.

The life cycle of the Heterophyes heterophyes begins when the adult trematodes release eggs that are already embryonated. Each egg contains miracidium that have fully matured. The eggs are expelled through the feces of the host and are consumed by a first intermediate host, a snail. Snails of the genera Pironella and Cerithidia make ideal hosts and are found in the Middle East and parts of Asia. Inside the snail, the eggs hatch to release miracidia which inhabit the intestine. 

The miracidia develop in to sporocysts, then rediae, then cercariae. As cercariae, they are released and encyst, consumed by freshwater fish that act as second intermediate hosts. Inside a fish, the cercariae develop into metacercariae. When the fish is consumed by a definitive host either undercooked, raw, or pickled, infection occurs. Either humans or fish eating mammals and birds can serve as definitive hosts. Inside the definitive host, the metacercariae exyst, attaching to the mucosa of the host’s small intestine where they reach adulthood. The adult form of the flukes can be 1.7 mm by 0.4 mm in size.

Heterophyiasis occurs in the Middle East, Far East, and Egypt. The clinical features of the disease include severe and fluctuating abdominal pain and diarrhea. When the eggs of the flukes move into the heart, fatal valvular and myocardial damage may occur. Such a case was recorded in the Philippines. There have also been instances of eggs migrating to various organs such as the brain.

Diagnosis of Heterophyiasis requires microscopy to find eggs in stool samples. Unfortunately, the eggs of the Heterophyes heterophyes are identical to the eggs of the Metagonimus yokogawai and very similar to those of the Opisthorchis and Clonorchis. Fortunately, there is treatment available in the form of a prescription medication called Praziquantel.