Clinical Presentation

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In humans, the clinical presentation of metagonimiasis has been shown to vary according to the level of infection and the parasite load. The main symptoms are diarrhea and colicky abdominal pain. In extremely rare cases, migration of the eggs to extra-intestinal sites (heart, brain) can occur, with resulting symptoms.

Metagonimiasis has an incubation period of 2 to 3 weeks. Clinical symptoms develop within this time period after the ingestion of fish containing live metacercariae. Following infection, a moderate degree of inflammation develops around the sites in the intestine where the worms are attached. This inflammation is frequently accompanied by microscopic sloughing or necrosis of the surrounding mucosal cells. The sucker attachments of the flukes irritate the mucosa, producing an excess of mucus and superficial erosion of the cells. At times they cause eosinophilic and neutrophilic infiltration of the wall, particularly around eggs that are deposited in the tissues. Very rarely, the adult M. yokogawai infiltrate the intestinal capillaries and lymphatics and are carried to the myocardium, brain, spinal cord, and other tissues where granulomatous changes may be provoked by their presence.

Usually the symptoms consist of mild diarrhea, but the extent of the symptoms depends on the number of worms present, the depth of their penetration into the wall, and the individual reaction of the patient. Once the worms invade the mucosa they remain there until thy die. Young children tend to have more severe symptoms, because they are more likely to suffer from dehydration and electrolyte imbalance associated with the diarrhea. 

A study entitled "Metagonomiasis in Korea", published in the Korean Journal of Parasitology in 1984 showed that eating just one raw sweetfish may result in severe abdominal pain, prostration and watery diarrhea. However, in endemic areas, many egg discharging patients were found to be asymptomatic. The development of symptoms appeared to mainly depend on the degree of infection. The duration of infection also seemed to affect the intensity of symptoms. The researchers (Cho, Kang and Lee) experimentally infected cats and dogs, and found that juvenile worms migrated and matured in crypts of Lieberkühn in the jejunum. After about five days, the adult M. yokogawai moved into the intervillous space. Adults rarely affected the submucosa or lymphatic tissues. In heavier infections, damage to the mucosa like villi fusion, villi shortening, slight hypertrophy of crypts, goblet cell depletion, inflammatory cell infiltration and shortening of microvilli was observed. These pathologic findings regressed spontaneously within 4 weeks of infection though adult worms still lived in the mucosa.