Trypanosoma lewisi

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Trypanosoma lewisi
Trypanosoma lewisi.jpg
Scientific classification Red Pencil Icon.png
Domain: Eukaryota
Phylum: Euglenozoa
Class: Kinetoplastea
Order: Trypanosomatida
Family: Trypanosomatidae
Genus: Trypanosoma
T. lewisi
Binomial name
Trypanosoma lewisi
(Kent, 1880)

Trypanosoma lewisi is a globally distributed parasite of Rattus species and other rodents such as mice, and of kangaroo rats in America. Among these host species were two endemic species of rats: Rattus macleari and Rattus nativitatis . Both are now believed to be extinct. It is not very clear whether or not the same parasite infected both species. However, both parasites are very similar. The northern rat flea ( Nosopsyllus fasciatus ) acts as the vector for the parasite, harboring the epimastigote stage in its midgut. [1] The trypomastigote is the stage that is present in the main host, the rodent. The epimastigote form attaches itself to the rectum of the insect using its flagella to burrow through the rectal walls. [2] The parasites also appear in the flea's feces. Ingestion of either the flea or its feces during grooming infects the host rodent with the parasites. [3] T. lewisi is normally non-pathogenic but is known to have produced fatal infections in rats. [4]



Trypanosomes in the blood of rats were first noted and described by Timothy Richards Lewis from Calcutta and the species was named after him. [5] In the 1900s, a parasitologist noticed that Rattus macleari , a species of rat endemic to Christmas Island, were becoming sick. The suspected cause was a species of trypanosomes. There was no proof that this was actually correct until scientists from the American Museum of Natural History deposited some rats that had been collected from Christmas Island as specimens into museums. Scientists argue that Trypanosoma lewisi is partially or wholly responsible for the subsequent extinction of Rattus macleari. The parasites were transmitted from fleas infesting the then recently introduced black rats ( Rattus rattus ). [6]


T. lewisi can be cultured in various media including in vivo in rat serum [7] and in vitro in mammalian cell culture media. [8] The parasite can also be grown in mice if the host is supplemented with a controlled diet and intraperitoneal injection of rat serum. [9] Ablastin, an antibody that arises during an infection in the host’s body, prevents the parasite from reproducing although they remain in adult form. [7]

A research paper suggests that the data on the aftermath of introduction of a Trypanosoma lewisi to immunologically naïve murine hosts on Christmas Island around 1900 matches reports of complete extinction within the range of 1–9 years. This gives some more information on the first pathogen introduction to a species to have caused species extinction. [6]

Although rare, there were also many cases in which human beings and primates were infected with Trypanosoma lewisi. In a recent study comparing Brazilian isolates in rats and primates, it was found the DNA sequences were the same when considering Trypanosoma lewisi. This further proves the potential of Trypanosoma lewisi's ability to infect human beings, despite being rare in most cases. [10]

Life cycle of Trypanosoma lewisi T. lewisi Life Cycle.pdf
Life cycle of Trypanosoma lewisi

Life cycle

A flea bites an infected rodent and ingests its blood. Within six hours, the parasites migrate and reproduce in the epithelial cells of their host flea's stomach. They then go further into the lumen of the stomach and finally move into the insect's rectum. [11] The parasite's metacyclic trypomastigote infects a rat after it eats the host flea or the flea's feces. Once inside the rat's body, the parasite will then begin reproducing epimastigotes in the blood capillaries of the host. After about five days, trypanosomes will begin appearing in the peripheral blood of the host, with the appearance of thick worms. These parasites are usually attacked by ablastin, a trypanocidal IgG antibody produced by their host's immune system beginning 2–4 days postinfection. [12] After a few weeks, the trypanosomes stop growing and disappear from the bloodstream. The rat then develops immunity against re-infection. [13]

Related Research Articles

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<i>Trypanosoma</i> Genus of parasitic flagellate protist in the Kinetoplastea class

Trypanosoma is a genus of kinetoplastids, a monophyletic group of unicellular parasitic flagellate protozoa. Trypanosoma is part of the phylum Sarcomastigophora. The name is derived from the Greek trypano- (borer) and soma (body) because of their corkscrew-like motion. Most trypanosomes are heteroxenous and most are transmitted via a vector. The majority of species are transmitted by blood-feeding invertebrates, but there are different mechanisms among the varying species. Some, such as Trypanosoma equiperdum, are spread by direct contact. In an invertebrate host they are generally found in the intestine, but normally occupy the bloodstream or an intracellular environment in the vertebrate host.

Maclears rat Extinct species of rodent

Maclear's rat is an extinct large rat endemic to Christmas Island in the Indian Ocean. It was one of two species of rat native to Christmas Island, alongside the bulldog rat. Abundant, unfamiliar with and seemingly unafraid of humans, large numbers of the creatures emerged and foraged in all directions at night. Making querulous squeaks, the rats entered the Challenger Expedition's tents and shelters in 1886, ran over sleepers, and upset everything in the search and fight for food. Maclear's rat might have been responsible for keeping the population of the Christmas Island red crab in check, as recent numbers of the crab are greater than in the past. It is thought that black rats inadvertently introduced by the expedition infected the Maclear's rats with a disease, which in turn could have contributed to the species' decline. The last recorded sighting was in 1903, although it is possible that Maclear's rats hybridized with black rats. A hard tick, described as an ectoparasite of Maclear's rat, is also thought to be extinct.

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<i>Pneumocystis jirovecii</i> Species of fungus

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<i>Toxascaris leonina</i> Species of roundworm

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Variant surface glycoprotein

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