Introduction
The intestinal fluke, Heterophyes heterophyes was first identified in 1851 by Theodor Maximillian Bilharz. This parasite was believed to be discovered during an Egyptian mummy autopsy. H. heterophyes is present in the Middle East, Asia, Africa, and West Europe. These organisms require various species to complete their complex lifestyle. Multiple mammals, including humans, act as the definitive hosts, snails act as the first intermediate host, and fish is the second intermediate. Humans, dogs, and cats are mammals that usually come in contact with these parasites. Snails (Cerithideopsilla conica) are affected by this parasite. Fish that might contain this parasite include Mugil cephalus, Aphanius fasciatus, Tilapia nilotica, and Acanthgobius species. Humans and mammals will come in contact with this parasite by consuming raw, contaminated fish. This parasite is one of the tiniest endoparasites that cause infections in humans. Symptoms of this infection usually range from intermittent abdominal pain and diarrhea to an ectopic infection. Sometimes the infection can be completely asymptomatic.
What Is the Causative Agent of Heterophyiasis?
H.heterophyes is a tiny trematode with a width of 1.4 to 0.5 millimeters. This trematode is covered with around 52 to 60 scale-like spikes. Their pharynx is completely developed and connected to the small intestine's cecum. Their mouth or sucker possesses spikes that cover their genital opening. Therefore they have only one hole responsible for both eating and reproducing. The testes are present side by side in the posterior region of the parasite. The ovaries are located right above the testes in the medial portion of the parasite. The acetabulum, or the ventral sucker, is located at the ventral side of the parasite. They attach themselves to the host with the help of this ventral sucker. The morphology of the parasite varies depending on the fish in which they live. These parasites are small teardrop-shaped flukes, usually in the small intestines of fish-eating mammals and birds. It is challenging to differentiate eggs from other related species; the estimate of human infection is not very accurate.
What Is the Life Cycle of the Fluke?
The adult parasites are embedded in the villi of the small intestine of the host. H. heterophyes take around four to six hours to reach the small intestines in the definitive host. The eggs that are deposited contain a miracidium. However, they do not hatch until they are ingested by a snail called Cerithidea cingulain Japan or Cerithideopsilla conica in Egypt. The miracidium becomes a sporocyst Inside the snail's gut and produces rediae. Then cercariae are produced by the rediae that exit the snail and move towards the surface of the water. In the water, they come in contact with fish and are transferred into the fish's epithelium. Here, the cercariae form cysts in the muscle. The second intermediate host of this parasite is the freshwater fish, including Mugil cephalus, Aphanius fasciatus, Acanthogobius species, and Tilapia nilotica. Finally, the parasite reaches the definitive host (humans and birds) by consuming raw or undercooked fish meat. Natural definitive hosts include humans, dogs, cats, wolves, foxes, and pelicans.
What Are the Risk Factors Associated With Heterophyiasis?
-
Individuals at high risk for this infection include fishermen and people working close to the bay waters.
-
Consumption of raw fish, typical food in these areas, leads to high endemicity. In endemic regions, individuals residing near river banks or lake shores show an increased intensity and a higher infection rate than those living far from these areas.
-
The inhabitants of these areas usually eat low-salted or undercooked fish that grow in contaminated or polluted water.
-
Another risk factor includes the common practice of people defecating on the river banks, lake shores, or from their boats. This can further lead to the transmission of this infection.
-
In Egypt, the rural areas are at a higher risk of being infected with H. heterophyes as they do not have easy access to medical services due to a lower socioeconomic status.
What Is the Pathology of Heterophyiasis?
These worms cause mild inflammation in the intestine when they come in contact with the intestinal wall. The infection can often be asymptomatic or cause slight intestinal discomfort. During early infection, this parasite begins cell apoptosis in the intestinal epithelial cell. Therefore, this infection can lead to:
-
Enlarged intestinal crypts.
-
Acute to chronic inflammation.
-
Atrophy, fusion, and shortening of the intestinal villi.
After early infection, this parasite will stop apoptosis which can cause a decrease in caspase-3 and NF-jB (proteins essential to induce programmed cell death or apoptosis).
Severe infections usually cause damage to the mucosa and produce intestinal pain and mucosal diarrhea. Sometimes these eggs enter the blood and vascular lymph systems through the mucosa and reach the ectopic sites in the body.
The tissue reaction in the valves affects the heart and myocardium, which cause heart failure. These eggs can also reach the brain or spinal cord, leading to neurological disorders and can also be fatal.
How Is Heterophyiasis Diagnosed?
Heterophyiasis can be diagnosed by stool examination. However, it is difficult when adult worms are absent because it is challenging to differentiate these eggs from the eggs of C. sinensis.
How Is Heterophyiasis Treated?
Heterophyiasis is treated with Praziquantel (a quinolone derivative). Praziquantel leads to deep lesions on the teguments of the parasite, and exposure to Praziquantel over a more extended period leads to even deeper lesions.
Conclusion
Twelve populations of the mud snail (Cerithideopsilla conica) were studied in Egypt. They are the carrier of Heterophyes heterophyes. Later, it was discovered that most infected snails were present in the Nile Delta.
Heterophyiasis species are present all around the world, and its cases have been recorded in Egypt, Brazil, India, Spain, Sudan, Israel, Turkey, Iran, and Russia. However, this infection is commonly present in North Africa, Korea, China, Asia, Japan, Taiwan, and the Philippines. The Heterophyes heterophyes are transmitted from a snail (Pirenella conica) to fish found in Northern African lagoons connected to the sea. The snails should be five millimeters or larger to transfer this parasite to the fish.
