What are the other Names for this Condition? (Also known as/Synonyms)

• Metagonimus Yokagawai Infection
• Yokogawai’s Fluke Infection

What is Metagonimiasis? (Definition/Background Information)

• Metagonimiasis is a parasitic infection, caused by Metagonimus yokogawai, more commonly known as Yokogawai’s fluke
• Consuming fish infested with the live larval form of the parasite results in the spread of infection to humans
• M. yokogawai are flatworms that reside in the intestines of their human host, feeding off digested nutrients
• These parasites have an incubation period of 2-3 weeks, and symptoms, such as diarrhea and abdominal pain, may develop within this incubation time
• A healthcare provider typically diagnoses Metagonimiasis upon examination of the stool for the presence of parasitic eggs, and then may prescribe anthelmintic medication for treatment
• The prognosis of Metagonimiasis is generally good with prompt and appropriate treatment

Who gets Metagonimiasis? (Age and Sex Distribution)

• Individuals of all ages, races, ethnic groups, and both genders are susceptible to Metagonimiasis
• The infection is more common among those living in certain geographic regions/nations of the Far East, Spain, Siberia, parts of China (Manchuria), the Balkan states (such as Bulgaria, Albania, Romania, etc.), and Israel

What are the Risk Factors for Metagonimiasis? (Predisposing Factors)

The risk factors of Metagonimiasis are as follows:

• Frequent consumption of undercooked or raw fish - the parasite most often resides in fish tissue
• Traveling to or living in regions with poor sanitary waste disposal. A lack of proper sanitation and fecal matter disposal can result in lakes and ponds having higher concentrations of fish infected with M. yokogawai, which may be then consumed by people in the area

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Metagonimiasis? (Etiology)

• Metagonimiasis is caused by the infection of the intestine by the parasitic Metagonimus yokogawai flatworm. The M. yokogawai is classified as an intestinal fluke/trematode and is among the smallest flukes that reside in humans
• The M. yokogawai parasite has a long etiological life cycle before residing in a human as its definitive (final) host
• The brackish water fish is the most common carrier of the parasite that directly transmits the infection to human hosts. The parasite encysts (remains inactive) inside the fish, until it is consumed by humans
• Humans are the definitive (final) host of the M. yokogawai. After ingestion, the parasite excysts (return to active form), attaching to the small intestines and maturing into adults
• From the attachment point in the small intestine, the parasite feeds on nutrients digested by the host. The attachment of the parasite to the intestinal wall often causes inflammation and cell necrosis (cell death) at the attachment point and surrounding areas of the small intestine

What are the Signs and Symptoms of Metagonimiasis?

The signs and symptoms of Metagonimiasis may vary in severity, depending on the extent and duration of infestation by the parasite, and may include:

• Diarrhea
• Severe abdominal pain
• Inflammation of the intestines around the infected areas
• Dehydration

How is Metagonimiasis Diagnosed?

The diagnosis of Metagonimiasis is made by the help of the following tests and exams:

• A complete physical examination and an assessment of symptoms
• Evaluation of the affected individual’s full medical history and recent travel history, if any
• Ova and parasites stool test, to detect the presence of the parasitic eggs in stool
  • However, eggs of this parasitic worm can often be physiologically similar to eggs of other parasites such as Heterophyes heterophyes, Chlonorchis, and Opisthorchis, thus making a definitive diagnosis of Metagonimiasis more difficult
  • Identifying the adult forms of the parasite in a stool sample after inducing their exit from the body by using an anthelminthic drug. This is often considered the method by which a healthcare provider can definitively diagnose infection by the M. yokogawai parasite

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Metagonimiasis?

The potential complications that could arise from Metagonimiasis may include the following:

• Chronic dehydration as a secondary symptom due to fluid and salt loss from diarrhea. This is more common in children than adults
• Invasion by the eggs of the parasite into the bloodstream, where they can travel to the brain, liver, and other vital tissues, inhibiting their function and potentially causing death

How is Metagonimiasis Treated?

Treatment of Metagonimiasis may include the following:

• Prescription anthelmintics, which are a class of medication that kills parasitic tapeworms in the body (without interfering with essential bodily functions), by either paralyzing or starving the tapeworms until they die, detach from the tissue they are attached to, and are excreted from the body
• Electrolyte therapy for rehydration, particularly children

It is important to note that there have been reported cases where the severity of symptoms has subsided without treatment, but the parasite was still present in the intestine. It is therefore important that any suspected cases of infection are brought to the attention of a healthcare provider.

How can Metagonimiasis be Prevented?

Prevention of Metagonimiasis may be possible by considering the following measures:

• Ensuring that fish and marine food are thoroughly cooked to prevent or greatly reduce the risk of infection. Metagonimiasis is most commonly contracted by consuming undercooked, infected fish
• Effectively disposing of waste in a sanitary manner, which is important for keeping water-dependent flukes such as M. yokogawai from infecting fish in public waters

What is the Prognosis of Metagonimiasis? (Outcomes/Resolutions)

The prognosis of Metagonimiasis is often good with proper administration of medication in a timely manner.

• Administration of anthelmintics drugs has proven to be very effective in complete removal of the M. yokogawai parasite from the body 
• Failure to seek appropriate medical care for this infestation can lead to the migration of the parasite eggs to vital organs, which may be life-threatening and potentially result in death

Additional and Relevant Useful Information for Metagonimiasis:

• Infection by M. yokogawai flatworm presents similar symptoms to Heterophyes heterophyes parasitic infection; however, the organisms have very different morphologies
• Metagonimiasis infection was first identified by two scientists, Yokogawai and Katsurda, in the early 1900s
• Mammals and birds that eat fish can also be infected by M. yokogawai