Metagonimiasis

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Metagonimiasis
Specialty	Infectious diseases, helminthologist

Metagonimiasis is a disease caused by an intestinal

, most commonly Metagonimus yokagawai, but sometimes by M. takashii or M. miyatai. The metagonimiasis-causing flukes are one of two minute flukes called the heterophyids. Metagonimiasis was described by Katsurasa in 1911–1913 when he first observed eggs of M. yokagawai in feces (date is disputed in various studies). M. takahashii was described later first by Suzuki in 1930 and then M. miyatai was described in 1984 by Saito.

Signs and symptoms

The main

.

Occasionally, flukes invade the mucosa and eggs deposited in tissue may gain access to circulation. This can then lead to eggs embolizing in the

cardiac insufficiency

.

An interesting case in Japan found

] Two months after administering praziquantel, the hemorrhages were gone, as was the diabetes. This unique case shows the potential of additional symptoms associated with metagonimiasis that are still unknown.

Cause

Metagonimiasis is most commonly caused by one of the two smallest flukes known to infect man, Metagonimus yokagawai, also called the

data on the three disease-causing agents also supported the nomination of M. miyatai as a separate species.

Trematodes are one class of phylum

.

Transmission

Transmission requires two intermediate hosts, the first of which is

Thiara granifera

.

Infection is acquired through the secondary intermediate host,

common carp

(Cyprinus carpio), Zacco temminckii, Protimus steindachneri, Acheilognathus lancedata, and Pseudorashora parva.

Definitive hosts include humans and various fish-eating mammals, primarily dogs, cats, and pigs. Fish-eating birds may also be infected with metagonimiasis.

Reservoirs

Reservoirs include fish-eating mammals such as dogs, cats and pigs as well as fish-eating birds. The presence of heterophyid infection in humans is generally caused by a lack of host specificity by the parasites, as seen in the many non-human reservoirs for metagonimiasis. The many reservoirs also have negative implications on the efficacy of prevention and eradication efforts of the disease.

Incubation period

The incubation period is around 14 days and infestation may persist for more than one year.

Morphology

Eggs

The morphology of the eggs is very important for diagnosis, but is difficult as eggs are very small. Eggs have a smooth, hard shell that is

, an "escape hatch" for the mircidium. The Clonorchis has more distinctive tapering and a seated operculum that help distinguish it more readily from Metagonimus species.

Adult flukes

The body of the adult disease-causing agent of metagonimiasis is often described as leaf-shaped, similar to most

organ

in the body. The size of the adult fluke does not exceed 2.5 mm length by .75 mm width.

Diagnosis

Metagonimiasis is diagnosed by eggs seen in

antibodies

to several parasite agents are important in serological diagnosis of acute parasitic disease and more research should be done on the efficacy of these methods of diagnosis.

Diagnosis may be difficult because the egg-laying capacity of

. It is important to ask where the person may have contracted the disease, find out if they have been to en endemic area, and check for signs and symptoms that would lead to metagonimiasis.

Prevention

Several public health prevention strategies could help lower the rates of metagonimiasis. One is to control the intermediate host (snails). This can be done through use of molluscidals. Another is to use education to ensure all people, especially in areas were the disease regularly occurs, fully cook all fish. This could potentially be problematic and not as effective as hoped as many of the people affected by metagonimiasis eat raw or pickled fish as part of a traditional, long-seated dietary practice. Additionally, implementing more sanitary water conditions would reduce the continual reintroduction of eggs to water sources, thus restarting the lifecycle. Complete control of metagonimiasis presents several potential problems because it does have several reservoir hosts, thus eradication is unlikely.

Treatment

(FDA) for treatment of metagonimiasis, but is approved for use on other parasitic infections.

Praziquantel has some side effects but they are generally relatively mild and transient and a review of evidence shows it overall a well-tolerated drug. Possible side effects include

recommended the use of Praziquantel in pregnant and lactating women, though controlled trials are still needed to verify this.

Another possible drug option is Tetrachloroethylene, a chlorinated hydrocarbon, but its use has been superseded by new antihelminthic drugs (like Praziquantel). A 1978 study also looked at the efficacy of several drugs on metagonimiasis infection, including bithionol, niclosamide, nicoflan, and Praziquantel. All drugs showed lower prevalence of eggs in feces, however only Praziquantel showed complete radical cure. Therefore, the authors concluded Praziquantel was the most highly effective, was very well tolerated, and was the most promising drug against metagonimiasis.

Epidemiology

Metagonimiasis infections are endemic or potentially endemic in 19 countries including Japan, Korea, China, Taiwan, the Balkans, Spain, Indonesia, the Philippines and Russia. Human infections outside endemic areas may result from ingesting pickled fish or sushi made from fish imported from endemic areas.

Korea

Food-borne trematodes are currently the most important parasitic infections in Korea and approximately 240,000 Koreans are believed to be currently infected. Of the 240,000 estimated to be infected, 120,000 are caused by M. yokagawai, 20,000 by M. takahashii, and 100,000 by M. miyatai. The national rate of infections among randomly selected people was 1.2% in 1981, 1.0% in 1986, and down to 0.5% in 2004. M. yokagawai infections are found mostly around the large and small streams where sweetfish live and have been identified as endemic foci. M. miyatai and M. takahashii are prevalent along the upper reaches of the big rivers where minnows and carps are caught for eating raw.

Japan

Metagonimiasis is also common in Japan, with 10-15% prevalence rates in populations bordering major rivers and 150,000 estimated infected. Food-borne trematodes are most common in rural areas where traditional food habits are more preserved and raw freshwater fishes are incorporated into the diet. Both clonorchiasis and metagonimiasis have become infections of higher social classes in Hong Kong and Japan, owing to their frequent consumption of raw fish.

India

There have also recently been two reported cases in India, a location in which occurrence of infection is almost unknown. The second case, in 2005, was in a 6-year-old female patient presenting with loose watery stools for four days (however more details were not obtained as the patient was both deaf and dumb since birth). Upon examination, M. yokagawai eggs were found in stool, but the patient left and further analysis and treatment could not be completed.

See also

• List of parasites (human)

References

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Ash, Lawrence; Orihel, Thomas. Atlas of Human Parasitology. Fourth Edition. American Society of Clinical Pathologists. 1997. Chai, Jong-Yil et al. "An epidemiological study of metagonimiasis along the upper reaches of the Namham River." Korean Journal of Parasitology. Vol. 31: 99–108. 1993.

Chi, Je G. et al. "Intestinal Pathology in Human Metagonimiasis with Ultrastructural Observation of Parasites." Journal of Korean Medical Science. Vol. 3: 171–177. 1998.

Despommier D.; Gwadz R.; Hotez P.; Knirsch C. Parasitic Diseases. Fifth Edition. New York: Apple Trees Productions. 2006. Doenhoff, M. J., D. Cioli, and J. Utzinger. "Praziquantel: mechanisms for action, resistance, and new derivatives for schistosomiasis." Current Opinion in Infectious Diseases. Vol 21:659-667. 2008.

FAO/NACA/WHO. "Food Safety Issues Associated with Products from Aquaculture." WHO Technical Report Series. Geneva, 1999.

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Rim, Han-Jong et al. "Antihelminthic Effects of Various Drugs against Metagonimiasis." Korean Journal of Parasitology. Vol. 16: 117–122. 1978.

Rim, Han-Jong. "Classification and host specificity of Metagonimus spp. from Korean freshwater fish." Korean Journal of Parasitology. Vol. 34: 7-14. 1996.

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Uppal, B. and V. Wadhwal. "Rare Case of Metagonimus Yokogawai." Indian Journal of Medical Microbiology. Vol. 23: 61–62. 2005.

WHO/FAO. "Food-Borne Trematode Infections in Asia." Ha Noi, Vietnam, 2002.

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WHO. "Review on the Epidemiological Profile of Helminthes and their Control in the Western Pacific region, 1997-2008." 2006.

Yamada, Shoko Merrit et al. "A Case of Metagonimiasis Complicated with Multiple Intracerbral Hemorrhages and Diabetes Mellitus." Journal of Nippon Medical School. 2008.

External links

• Metagonimiasis