Metagonimiasis

Metagonimiasis is a disease caused by an intestinal trematode, 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. Metagonimiasis is a disease caused by an intestinal trematode, 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. The main symptoms are diarrhea and colicky abdominal pain. Because symptoms are often mild, infections can often be easily overlooked but diagnosis is important. Flukes attach to the wall of the small intestine, but are often asymptomatic unless in large numbers. Infection can occur from eating a single infected fish source. Peripheral eosinophilia is associated especially in early phase. When present in large numbers, can cause chronic intermittent diarrhea, nausea, and vague abdominal pains. Clinical complaints can also include lethargy and anorexia. In acute metagonimiasis, clinical manifestations are developed only 5–7 days after infection. Heavy infection has also been associated with epigastric distress, fatigue, and malaise. Occasionally, flukes invade the mucosa and eggs deposited in tissue may gain access to circulation. This can then lead to eggs embolizing in the brain, spinal cord, or heart. Granulomas may form around eggs and can cause seizures, neurologic deficits, or cardiac insufficiency. An interesting case in Japan found diabetes mellitus (DM) to be a sign of chronic infection with intracerebral hemorrhages as the acute sign of aggravation{{citation needed}}. 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. Metagonimiasis is most commonly caused by one of the two smallest flukes known to infect man, Metagonimus yokagawai, also called the Japanese fluke. More rarely, metagonimiasis can arise from infection with M. takahashii or M. miyatai. Recent studies analyzing the DNA of the three agents causing metagonimiasis found that DNA sequencing supports M. yokagawai and M. takahashii be placed in the same clade, and phylogenic tree analysis supports their genetic similarity. M. miyatai, however, was found to be more genetically distinct, and the authors concluded it should be nominated as a separate species. An additional study examining karyotype data on the three disease-causing agents also supported the nomination of M. miyatai as a separate species. Trematodes are one class of phylum Platyhelminthes from the order Digenia and are generally referred to as flukes. Metagonimiasis is of the family Herterophyidae. Transmission requires two intermediate hosts, the first of which is snails, most commonly of species Semisucospira libertina, Semiculcospira coreana, 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.