Gastrodiscoides

Gastrodiscoides
Adult G. hominis
Scientific classification
Kingdom: Animalia
Phylum: Platyhelminthes
Class: Trematoda
Subclass: Digenea
Order: Echinostomida
Family: Paramphistomidae
Genus: Gastrodiscoides
Leiper, 1913
Type species
Gastrodiscoides hominis
(Lewis and McConnell, 1876) Leiper, 1913

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;[1][2] with isolated cases from Africa, such as Nigeria.[3]

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.[4][5]

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.[6]

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.[7] 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.[6] 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,[8] 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.[9]

Description

It is typically an amphistome with the ventral sucker close to the posterior end. The body is bilaterally symmetrical and is acoelomate. It is dorsoventrally flatted, with unique pyramidal shape. The body is covered by a tegument bearing numerous tubercles.[10] The alimentary canal is incomplete consisting of a pair of lateral pouches arising from the oral sucker and a pharyngeal tube, which bifurcates into two gut caeca. The bladder is in the middle behind the ventral sucker. Being hermaphrodite, both male and female reproductive system are present.[4][6]

Biology

Humans are now considered as the accidental host because humans are not the primary requirement for the life cycle. In fact, pigs are recognised as the principal definitive host. Infection causes a helminthic disease called gastrodiscoidiasis.[4] It is a digenetic trematode with a complex life cycle involving asexual reproduction in an intermediate host (presumably aquatic snails), and sexual reproduction in the vertebrate host. As a hermaphrodite, eggs are produced by self-fertilisation and are released along the faeces of the host. In water, eggs into miracidia which then infect a mollusc, in which larval development and fission occurs. Infective cercariae are produced and are released on water plants or directly infect other aquatic animals, such as fish.[11] Therefore, humans and other mammals are infected through eating contaminated vegetables and raw or undercooked fish. Infection is generally mild and asymptomatic. However, heavy infection in humans is suspected to cause diarrhoea, fever, abdominal pain, colic, malnutrition, anaemia, and even amounting to death.[1][3]

References

  1. 1 2 Mas-Coma S, Bargues MD, Valero MA (2006). "Gastrodiscoidiasis, a plant-borne zoonotic disease caused by the intestinal amphistome fluke Gastrodiscoides hominis (Trematoda:Gastrodiscidae)". Revista Ibérica de Parasitología. 66 (1-4): 75–81. ISSN 0034-9623.
  2. ↑ Kumar V (1980). "The digenetic trematodes, Fasciolopsis buski, Gastrodiscoides hominis and Artyfechinostomum malayanum, as zoonotic infections in South Asian countries". Ann Soc Belg Med Trop. 60 (4): 331–339. PMID 7016049.
  3. 1 2 Dada-Adegbola HO, Falade CO, Oluwatoba OA, Abiodun OO (2004). "Gastrodiscoides hominis infection in a Nigerian-case report". West African Journal of Medicine. 23 (2): 185–186. doi:10.4314/wajm.v23i2.28116. PMID 15287303.
  4. 1 2 3 Liu D (2012). Molecular Detection of Human Parasitic Pathogens. Boca Raton, FL: CRC Press. pp. 365–368. ISBN 1-4398-1242-X.
  5. ↑ Müller R, Wakelin D (2001). Worms and Human Disease. CABI Publishing, Oxon, UK. pp. 55–56. ISBN 0851995160.
  6. 1 2 3 Khalil M (1923). "A description of Gastrodiscoides hominis, from the Napu mouse deer" (PDF). Proceedings of the Royal Society of Medicine. 16 (1): 8–14. PMC 2103306Freely accessible. PMID 19983413.
  7. ↑ Leiper RT (1913). "Observations on certain helminths of Man". Transactions of the Royal Society of Tropical Medicine & Hygiene. 6 (8): 265–297. doi:10.1016/S0035-9203(13)90201-7.
  8. ↑ Buckley JJC (1939). "Observations on Gastrodiscoides hominis and Fasciolopsis in Assam". Journal of Helminthology. 17 (1): 1–12. doi:10.1017/S0022149X00030972.
  9. ↑ Buckley JJC (1964). "The problem of Gastrodiscoides hominis (Lewis and McConnell, 1876) Leiper, 1913". Journal of Helminthology. 38 (1-2): 1–6. doi:10.1017/S0022149X00033514. PMID 14125103.
  10. ↑ Tandon V, Maitra SC (1983). "Surface morphology of Gastrodiscoides hominis (Lewis & McConnell, 1876) Leiper, 1913 (Trematoda: Digenea) as revealed by scanning electron microscopy". Journal of Helminthology. 57 (4): 339–342. doi:10.1017/s0022149x00011056. PMID 6668422.
  11. ↑ Dutt SC, Srivastava HD (1972). "The life history of Gastrodiscoides hominis (Lewis and McConnel, 1876) Leiper, 1913--the amphistome parasite of man and pig". Journal of Helminthology. 46 (1): 35–46. PMID 5038423.

External links

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