Murine Trypanosomiasis

Trypanosoma lewisi is the causative agent of murine trypanosomiasis in domestic rats throughout much of the world. It is principally transmitted by the Northern rat flea (N. fasciatus) and the Oriental rat flea {X. cheopis). Fleas imbibe trypanosomes while feeding on infected rats; the pathogen remains in the flea midgut where development occurs. Within 6 hr after ingestion, the trypanosomes invade midgut epithelial cells, transform into pear-shaped forms, and begin to divide. The parasitized gut cells rupture after 18 hr to 5 days to release the trypanosomes; these then either invade new epithelial cells to repeat the process or move posteriorly to the rectum and anus. Trypanosomes in this "rectal phase" are voided in the flea feces. The trypanosomes enter their rat hosts when the latter lick and scratch their fur during grooming, representing a classic example of posterior-station transmission. Murine trypanosomiasis is usually a benign infection in rats. However, the T. lewisi-ftta-rat system has been used as a laboratory model for devising therapies and studying the development of immunity against more virulent trypanosome species that are pathogenic to humans and domestic animals.

At least nine species of trypanosomes other than T. lewisi are transmitted to rodents by fleas. Rodent trypanosomes with confirmed flea transmission cycles include T. musculi (synonym: T. duttoni) of house mice, T. rabinowitschi of hamsters, T. neotomae of wood rats, and T.grost of the European wood mouse (Apodemus syl-vaticus). T. nabiasi is one of two species of trypanosomes known to be transmitted to rabbits by fleas. Fleas are also suspected as vectors of trypanosomes associated with some birds, shrews, voles, and lagomorphs.

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