Metagonimus yokogawai infection

Metagonimus yokogawai infection

Description, Causes and Risk Factors:

A genus of flukes (superfamily Heterophyundea) that encyst on fish and infect various fish-eating animals, including humans. Metagonimus yokogawai, an intestinal fluke widely distributed in the Far East and the Balkans and one of the smallest (1-2.5 mm) flukes infecting humans, is passed from Semisulcospira snails to cyprinoid fish and then to humans and other fish-eating mammals and birds.

Metagonimus yokogawai

Metagonimus yokogawai infection caused by an intestinal trematode, most commonly Metagonimus yokogawai (M. yokogawai), but sometimes by M. takashii or M. miyatai. The metagonimiasis causing flukes are one of two minute flukes called the heterophyids.

Transmission requires two intermediate hosts, the first of which is snails, most commonly of species Semisucospira libertine, Scoreana, and Thiara granifera. Infection is acquired through the secondary intermediate host, fish, that haven't been thoroughly cooked. Metacercariae encyst under the scales or in the flesh of fish from fresh or brackish water. Sweetfish (Pecoglossus altevelis) is one of the most common fish species infected, but other include the golden carp (Carassius auratus), 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.

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

Death from infection is rare and usually occurs only in persons with a heavy worm burden who present with severe cachexia and prostration. Other intercurrent infection may also cause death. In cases of infection with H heterophyes or M yokogawai, death may occur after embolization of the eggs to the heart or brain. Embolization to the brain and spinal cord can also cause focal neurologic disease.

Research: An epidemiological survey on Metagonimus yokogawai infection was performed in the eastern coast area of Kangwon province. Formalin-ether concentration technique and Stoll's dilution egg counting method were employed to figure out the prevalence and intensity of M. yokogawai infection and eating habits of inhabitants with raw freshwater fish. The results are summarized as follows: The prevalence rate of M. yokogawai infection was 6.6% among a total of 2,357 examinees; 8.6% (115 out of 1,345) in male and 4.0% (40 out of 1,012) in female. The prevalence rates were different by the streams where the examinees were residing: 17.8% along the area of Ohsip-cheon (stream), 11.8% along Maeup-cheon, 1.7% along Hwasang-cheon, 1.3% along Yeongok-cheon, 0.9% along Namdae-cheon, 0.9% along Sa-cheon and 0% in the other streams (Yongchon-cheon, Kangnung Namdae-cheon and Jusoo-cheon) in decreasing order. By social strata, the positive rate was 8.0% (122 out of 1,521) in general inhabitants and 3.9% (33 out of 836) in school children. By the intensity of infection by means of EPG counts in feces; the light infection (less than 400/EPG) was 74.1%, moderate infection (401-1,000/EPG) 17.3% and heavy infection (more than 1,001/EPG) 8.6%. Twelves out of 50 sweetfish (Plecoglossus altivelis) (24%) caught from the streams in eastern coast of Kangwon-Do were infected with metacercariae of M. yokogawai, and the number of larvae detected were 70.7 per fish in average. The metacercarial infection rate in fish were also different by the streams; 100% in Ohsip-cheon of Samcheok-Gun, 14.3% in Sa-cheon, 16.7% in Yeongok-cheon of Myeongju-Gun and 0% in Namdae-cheon of Yangyang-Gun, respectively. Six hundred ninety five (695) out of 1,396 inhabitants and school children (49.8%) were experienced in eating raw freshwater fishes (Plecoglossus altivelis, Tribolodon hakonensis, Coreoperca sp., Moroco sp., Carassius sp. & Cyprinus sp. and Zacco platypus). The data were assayed with the questionnaire collected from the examinees. In summarizing the above results, it is known that the Ohsip-cheon area of Samcheok-Gun is highly infected region, and the other areas of Kangnung Namdae-cheon, Yeongok-cheon and Yangyang Namdae-cheon are very lowly infected or non-infected regions for M. yokogawai infection.


Symptoms may include the following:

    Peripheral eosinophilia.

  • Diarrhea.

  • Nausea.

  • Abdominal pain.

  • Lethargy.

  • Fatigue.

  • Anorexia.

  • Malaise.

  • Seizures (in extreme cases).

  • Neurological defects (in extreme cases).

  • Cardiac problems (in extreme cases).


A 1993 analysis of the efficacy of ELISA tests to diagnose Metagonimus yokogawai infection implied that simultaneous screening of specific 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 heterophyidae is limited, and therefore sedimentation concentration procedures may be needed to demonstrate eggs in lighter infections. Accurate species identification is also difficult because eggs of most flukes are similar in size and morphology, especially those of Heterophyes heterophyes, Clonorchis and Opisthorchis. 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.


The merthiolate, iodine, formalin (MIF) method is used to detect intestinal fluke parasites. The MIF method was established early as a versatile and accurate technique for identifying intestinal protozoa in stool and fecal samples. The technique simultaneously preserves and stains stool specimens, which can then be examined with direct smear techniques.

Various polymerase chain reaction (PCR) methods have shown potential in detecting Metagonimus yokogawai infection. These methods take advantage of the different types of DNA nucleotide sequence variations demonstrated by the different species of parasites within a particular genus.

Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and simple sequence repeat anchored PCR have been reported to be useful in distinguishing among species of the Metagonimus genus (including M yokogawai). These methodologies are based on differences in restriction fragment length polymorphisms and simple sequence repeats among the species. Information derived from RFLP involving specific sites in ribosomal RNA and mitochondrial cytochrome oxidase I (mtCOI) genes may help to differentiate M yokogawai from other Metagonimus species.


Praziquantel is recommended in both adult and pediatric cases with dosages of 75 mg/kg/d in 3 doses for 1 day. Praziquantel is a praziniozoquinoline derivative that alters the calcium flux through the parasite tectum and causes muscular paralysis and detachment of the fluke. Prizaquantel should be taken with liquids during a meal and as provided commercially as Biltricide. Praziquantel is not approved by the U.S. Food and Drug Administration (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 abdominal pain, allergy, diarrhea, headache, hepatic dysfunction/hepatitis, nausea or vomiting, exacerbation of porphyries, pruritus, rash, somnolence, vertigo, or dizziness. In fact, in 2002, the World Health Organization (WHO) 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, 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.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.



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