Parasites and Pestilence: Infectious Public Health Challenges

Sarah Scheller


TABLE OF CONTENTS : Introduction Agent History of Discovery Clinical Presentation Transmission Reservoir and Vector Information Life Cycle Morphology Diagnostic Tests Incubation Period Management and Therapy Epidemiology Public Health and Prevention Links and Sources


Gastrodiscoidiasis is an infection that is usually asymptomatic and affects the small intestine. It is caused by a trematode (fluke) named gastrodiscoides hominis. You can find this large flatworm mostly in small villages in a state in the Northeast corner of India called Assam. Gastroiscoides hominis is usually found in animals (pigs), but when it infects humans can cause serious health problems and even mortality. It is also known as a Digenean Fluke which is a subclass of platyhelminths that consists of over 6000 parasitic flatworms that affect mostly the digestive tract. Although gastrodiscoidiasis is not seen as a serious health threat yet, it is not an infection to take lightly.

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Phylum Platyhelminths
Class Trematoda
Family Amphistomidae
Genus Gastrodiscoides Hominis

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Gastrodiscoidiasis was first brought to attention in 1939 by J.J.C. Buckley. In a paper titled, Observations on Gastrodiscoides hominis and Fasciolopsis in Assam, Buckley described the life cycle and prevalence of the disease in the state of India (Assam). He found in 1939 that three villages surveyed in Assam over 40% of the population was infected. Later in life, it was Buckley who was responsible for the formal classification of this parasite.

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While this parasite is typical found in pigs, it can also affect humans. Usually the infection is asymptomatic but occasionally it can also cause intestinal problems such as diarrhea, fever, abdominal pain, colic, and an increase in mucous production. In severe cases, where there may be large amounts of eggs present, tissue reactions can occur in the heart or mesenteric lymphatics.

Example of a Case in Nigeria taken from the Department of Medical Microbiology and Parasitology, College of Medicine , University of Ibadan , Nigeria .

Gastrodiscoides hominis is a large fluke of pig and human and constitutes an important parasite of human in Assam , Indian, the Philippines and Southeast Asia . This parasite has not been reported in Nigeria and possibly other parts of Africa . This is a case report of a seven year old Nigerian child who presented with features of malnutrition and anaemia and was found to have Gastrodiscoides hominis and Ascaris lumbricoides. Following clearance of the worms there was tremendous improvement of the health status of the child. The detailed epidemiology of this parasite still remains to be studied in this environment.

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Gastrodiscoides Hominis is passed through the feces in egg form where it can come into direct contact with the water supply or vegetation or it is used as "night soil". This parasite is then usually transmitted through the ingestion of vegetation found in contaminated water such as water caltrop where the parasite tends to reside after leaving its intermediate host (the snail). It can also be transmitted after eating infected fish that has not been cooked properly or at all.

Woman pouring feces in garden in Indian

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Reservoir Pigs, Monkeys, Rats, Fish, and other fish-eating animals
Vector No known

Humans are considered an accidental host because the parasite can survive without the existence of man. However, the snail intermediate host is necessary in the development of the parasite.

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1) The eggs of G. Hominis are passed in feces unfertilized usually into some kind of water source where they are ingested by the snail intermediate host. The eggs hatch and release miracidium which develop from there into the sporocyst stage followed by one or more generations of redia. Finally, the redia transform into the cercarial stage (which have a "keeled" tale). This entire process occurs in under 20 days typically.

2) The cercaria search and penetrate a second intermediate host, such as a fish, where they encsyt as metacercaria. These metacercaria can attach to vegetation (where "night soil" is used) or remain in the fish.

3) This intermediate host may or may not exist.

4) The final host (man) ingests the metacercaria (approximately 30-150 days after being in the snail) either by the infected fish or contaminated vegetation. The parasite travels through the GI tract into the duodenum then continues down the intestine where it self-fertilizes. It then moves to the cecum and ascending colon where it attaches and lays hundreds of eggs. Finally the eggs are passed through the feces.

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G. Hominis is a reddish-colored amphistome with a ventral sucker located in the posterior end. The anterior region is narrow and ends with a rounded tip. The posterior region contains the reproductive organs including an ovary in the shape of an oval located under the 2 lobed testes. The testes are found below the gut ceacae and are in front of the the vitellaria that surround the intestinal caecae. The eggs are a greenish-grey color and rhomboidal in shape. They measure (130-160mm x~70mm) and are passed through the feces. The entire egg is about 4-6 x 5-10 mm in size.

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The diagnosis is made through examination of the feces and detection of G. Hominis eggs. Only after several digestions of the parasite can the higher levels be detected because the patient begins to present the symptoms mentioned before. There have not been any other tests made at this time.

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There is no exact timing on the incubation period because most of the cases are asymptomatic, but it is estimated that it takes a few days for the parasite to move through the entire GI tract and finally reach the cecum.

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The treatment for G. Hominis is similar to those of M. yokogawai or H. heterophyes in that typically a soapsud enema can be effective in removing the worms. It works to flush the flukes from the colon which removes the parasite entirely since it does not reproduce within the host.

Some drugs that have been proven effective are tetrachlorothyline (given 0.1mg/kg on an empty stomach) and the preferred drug- prazinquantal which is less toxic and eliminates most of the parasite with 3 doses (at 25mg/kg) in one day.

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G. Hominis can be found in Vietnam, Philippines, Bangladesh, and most commonly in the Assam state of India. It is prevalent in areas that use "night soil" like in Southeast and Central Asia. A few cases have been documented in Nigeria.

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Prevention of this disease is not difficult when simple sanitary measures are taken. "Night Soil" should never be used as a fertilizer because it could contain any number of parasites. Also, all food should be washed thoroughly using filtered water and proper techniques to dispose of waste should observed.

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Photo with short description:

Photo and Description of other Trematodes:

Description of Digenea:

Good Description of Trematodes in General:

Good Site on "Night Soil" Sanitation Practices ter/2003/projectwash.html

Good Articles:

Buckley, J. J. C. Observations on Gastrodiscoides hominis and Fasciolopsis in Assam . J. Helminthol., 17 (1939): 1-12.

Go, Chi Hiong U. Intestinal Flukes. eMedicine, (2003): 1-11.

Bunnag T, Sornmani S, Impand P: Potential health hazards of the water resources development: a health survey in the Phitsanulok Irrigation Project, Nan River Basin, Northern Thailand. Southeast Asian J Trop Med Public Health, 1980 Dec; 11(4): 559-65

Mas-Coma S, Bargues MD, Valero MA. Fascioliasis and other plant-borne trematode zoonoses. Int J Parasitol, 2005 Oct;35(11-12):1255-78.

Weisher, B. An Introduction to Nematodes: General Nematology. Sofia , Bulgaria : Pensoft Publishers, 2000.

Contact Information:

Sarah Scheller, 2006,
Stanford University
Parasites & Pestilence: Infectious Public Health Challenges
Prof. D. Scott Smith,

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