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Gastrodiscoides
''Gastrodiscoides'' is genus of zoonotic fluke under the class Trematoda. It has only one species, ''Gastrodiscoides hominis''. It is a parasite of a variety of vertebrates including human. In fact the first definitive specimen was described from human subject in 1876. It is prevalent in Bangladesh, India, Burma, China, Kazakhstan, Philippines, Thailand, Vietnam, and Volga Delta in Russia; with isolated cases from Africa, such as Nigeria.
Its natural habitat is the colon of pigs, and has also been found in rhesus monkey, orang-utan, fish, field rats and Napu mouse-deer. In humans the habitat is on the wall of the caecum.
==History of discovery==
The worm was discovered and described by two British medical doctors, Timothy Richard Lewis and James McConnell in 1876, from the caecum of an Assamese man in India. Their description of the internal structure was inaccurate and incomplete. They claimed that the parasite had one testis and one ovary. They placed it in the genus ''Amphistomum'', because of its obvious location of posterior sucker; hence named ''Amphistomum hominis'', as it was found in human. In 1902, F. Fischoeder recognised the affinity with other species and tentatively placed it in the genus ''Gastrodiscus'' (Leuckart, 1877). However, the generic name was largely recognised as synonym; hence known as ''Amphistomum (Gastrodiscus) hominis''. With a fresh look, J.W.W. Stephens redescribed the parasite in 1906, and clearly noted the overlooked relatively small ovary and interpretation of the posterior testis as an ovary in the original description. But he nonetheless succumbed to the prevailing taxonomic position.
Then a blooming helminthologist at the London School of Tropical Medicine, Robert T. Leiper re-examined the parasite in 1913. He noted the distinctive characters such as: (1) tuberculated genital cone; (2) position of genital orifice; (3) smooth ventral disc; and (4) testes in tandem position. These outstanding features prompted him to create an entirely novel genus ''Gastrodiscoides'' for the specimen. This taxonomic revision was not without its criticism, as some of the descriptions were later found to be flawed, such as the position of testes. So it did not gain consensus acceptance. To make the matter worse, and to an embarrassment on the specific epithet, it came to light that the parasite was much more common to pigs and other mammals than in humans. The first report of infection of pigs was in Cochinchina, Vietnam, in 1911. In 1913, it was further confirmed that the rate of porcine infection was as high as 5%. Then a large number of living flukes was recovered from dead Napu mouse-deer at the Zoological Gardens of the Zoological Society of London. The mouse-deer was Prince of Wales's collection from Malay. Notwithstanding the shortcomings of Leiper's descriptions, the generic name ''Gastrodiscoides'' became more and more advocated in the early 1920s.〔 The currently accepted nomenclature was fortified by a British parasitologist, J.J.C. Buckley, at the London School of Hygiene and Tropical Medicine, whose descriptions were based on high incidence of the parasitism among the Assamese in India. From his first report in 1939, then followed by a body of evidences in support of Leiper's proposition, Buckley helped to vindicate the validity of a separate genus ''Gastrodiscoides'', hence the binomial ''Gastrodiscoides hominis''.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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