Heterophyes Heterophyes

Adult specimen stained with carmine


Heterophyes heterophyes is a human parasite.

Geography

Common in north Africa, Asia Minor, Korea, China, Japan, Taiwan, and the Philippines.

Morphology

Minute teardrop-shaped flukes found in the small intestines of fish-eating birds and mammals. The eggs are hard to tell apart from other related species so there is no accurate estimate of human infection. The adult flukes range from 1.0mm to 1.7mm long and about 0.35mm at their greatest width. The body of the fluke is covered in scales mostly concentrated at the anterior end. Also at the anterior end is an oral sucker. Located in the medioanterior of the body is the acetabulum. At the posterior end of the fluke are two oval testes. The vas deferens leading from the testes expands to form a seminal vesicle and then narrows again to form an ejaculatory duct. The fluke also has female reproductive organs. Located medioposterior is the fluke's one ovary and leading away from the ovary is the vitellaria. The uterus is a long tube like structure that also leads away from the ovary and joins up with the ejaculatory duct to form the genital duct which leads to a genital sinus. The sinus leads to the genital pore which is lined with 60-90 toothed spines. The genital pore is where the fluke releases its eggs.

Biology

The adult flukes live burrowed between the villi of the host's small intestine. The eggs that are laid contain a miracidium but do not hatch until they are ingested by a snail (Pirenella conica in Egypt or Cerithidia cingula in Japan). Inside the snails gut, the miracidium becomes a sporocyst which then begin to produce rediae. The rediae produce cercariae which then exit the snail, swim toward the surface of the water, and slowly fall back down. On their way down, they contact a fish and penetrate into the epithelium of the fish. Here, the cercariae encyst in the muscle tissue. The definitive host, such as humans or birds, eats the undercooked or raw meat of a fish and ingest the parasite.

Epidemiology

People at high risk for infection are those who live by bay waters including fishermen. Infection is acquired by eating raw fish, a common food in areas of heavy endemicity. In endemic areas, people who live near lake shores or river banks usually have a higher rate and intensity of infection than those living a distance from such areas. It is possible that inhabitants of these areas eat more low-salted or improperly cooked fish and that their fish are obtained from polluted water. It is common practice for people to defecate on the lake shores and river banks or from their boats while fishing.

Pathology

Each worm causes a mild inflammatory reaction at its site of contact with the intestine. In heavy infections which are common cause damage to the mucosa and produce intestinal pain and mucosa diarrhea. Sometimes eggs can enter the blood and lymph vascular systems through mucosa go into the ectopic sites in the body. The heart can be affected with tissue reaction in the valves and myocardium that cause heart failure. Eggs can also get into the brain or spinal cord and cause neurological disorders and sometimes fatalities.

Diagnosis

Diagnosis done by stool examination is difficult when adult worms are not present because the eggs are hard to distinguish from C.sinensis.

Treatment

Praziquantel, a quinolone derivative.

References

  • Roberts, Larry, and John Janovy. Gerald D. Schmidt & Larry S. Roberts' Foundations of Parasitology. 8th ed. New York: McGraw-Hill, 2009. 291-92. Print.
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