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Heterophyiasis

[Heterophyes heterophyes]

Causal Agents

The trematode Heterophyes heterophyes, a minute intestinal fluke.


Life Cycle

lifecycle

Adults release embryonated eggs each with a fully-developed miracidium, and eggs are passed in the host's fecesThe number 1 . After ingestion by a suitable snail (first intermediate host), the eggs hatch and release miracidia which penetrate the snail’s intestineThe number 2. Genera Cerithidia and Pironella are important snail hosts in Asia and the Middle East respectively. The miracidia undergo several developmental stages in the snail, i.e. sporocystsThe number 2a, rediaeThe number 2b, and cercariaeThe number 2c. Many cercariae are produced from each redia. The cercariae are released from the snailThe number 3 and encyst as metacercariae in the tissues of a suitable fresh/brackish water fish (second intermediate host)The number 4. The definitive host becomes infected by ingesting undercooked or salted fish containing metacercariaeThe number 5. After ingestion, the metacercariae excyst, attach to the mucosa of the small intestineThe number 6 and mature into adults (measuring 1.0 to 1.7 mm by 0.3 to 0.4 mm)The number 7. In addition to humans, various fish-eating mammals (e.g., cats and dogs) and birds can be infected by Heterophyes heterophyes The number 8.

Geographic Distribution

Egypt, the Middle East, and Far East.

Clinical Presentation

The main symptoms are diarrhea and colicky abdominal pain. Migration of the eggs to the heart, resulting in potentially fatal myocardial and valvular damage, has been reported from the Philippines. Migration to other organs (e.g., brain) has also been reported.

 

Adult of Heterophyes heterophyes.

 

Adults of Heterophyes heterophyes are minute flukes, measuring 1-2 mm in length. The tests are large and paired, and are situated near a small ovary. The surface of the worm is covered with minute spines. Adults reside in the small intestine of the definitive host.
Figure A

Figure A: Adult of H. heterophyes, stained with carmine. In this figure, the following structures are labeled: oral sucker (OS), pharynx (PH), intestine (IN), ventral sucker, or acetabulum (AC), and eggs within the uterus (UT)

Snail intermediate hosts of Heterophyes heterophyes.

 

Like all trematodes, Heterophyes heterophyes requires a snail as an intermediate host. Cerithideopsilla cingulata is the main first intermediate host for H. heterophyes in southeast Asia.
Figure A

Figure A: Cerithideopsilla cingulata, an intermediate host for H. heterophyes in southeast Asia. Image courtesy of Conchology, Inc, Mactan Island, Philippines

Laboratory Diagnosis

The diagnosis is based on the microscopic identification of eggs in the stool. However, the eggs are indistinguishable from those of Metagonimus yokogawai and resemble those of Clonorchis and Opisthorchis.

Treatment Information

Praziquantel* is the drug of choice.

Praziquantel

Oral praziquantel is available for human use in the United States.

Praziquantel is pregnancy category B. There are no adequate and well-controlled studies in pregnant women. However, the available evidence suggests no difference in adverse birth outcomes in the children of women who were accidentally treated with praziquantel during mass prevention campaigns compared with those who were not. In mass prevention campaigns for which the World Health Organization (WHO) has determined that the benefit of treatment outweighs the risk, WHO encourages the use of praziquantel in any stage of pregnancy. For individual patients in clinical settings, the risk of treatment in pregnant women who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.

Pregnancy Category B: Either animal-reproduction studies have not demonstrated a fetal risk but there are no controlled studies in pregnant women or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the first trimester (and there is no evidence of a risk in later trimesters).

Praziquantel is excreted in low concentrations in human milk. According to WHO guidelines for mass prevention campaigns, the use of praziquantel during lactation is encouraged. For individual patients in clinical settings, praziquantel should be used in breast-feeding women only when the risk to the infant is outweighed by the risk of disease progress in the mother in the absence of treatment.

The safety of praziquantel in children aged less than 4 years has not been established. Many children younger than 4 years old have been treated without reported adverse effects in mass prevention campaigns and in studies of schistosomiasis. For individual patients in clinical settings, the risk of treatment of children younger than 4 years old who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.

* This drug is approved by the FDA, but considered investigational for this purpose.

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DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.

  • Page last reviewed: May 3, 2016
  • Page last updated: May 3, 2016
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