Phylogenetic, morphological and behavioural analyses support host switching of Trypanosoma (Herpetosoma) lewisi from domestic rats to primates.

We characterized four Brazilian trypanosomes isolated from domestic rats and three from captive non-human primates that were morphologically similar to T. lewisi, a considered non-pathogenic species restricted to rodents and transmitted by fleas, despite its potential pathogenicity for infants. These isolates were identified as T. lewisi by barcoding using V7V8 SSU rDNA sequences. In inferred phylogenetic trees, all isolates clustered tightly with reference T. lewisi and T. lewisi-like trypanosomes from Europe, Asia and Africa and despite their high sequence conservation formed a homogeneous clade separate from other species of the subgenus T. (Herpetosoma). With the aim of clearly resolving the relationships between the Brazilian isolates from domestic rats and primates, we compared sequences from more polymorphic ITS rDNA. Results corroborated that isolates from Brazilian rats and monkeys were indeed of the same species and quite close to T. lewisi isolates of humans and rats from different geographical regions. Morphology of the monkey isolates and their behaviour in culture and in experimentally infected rats were also compatible with T. lewisi. However, infection with T. lewisi is rare among monkeys. We have examined more than 200 free-ranging and 160 captive monkeys and found only three infected individuals among the monkeys held in captivity. The findings of this work suggest that proximity of monkeys and infected rats and their exposure to infected fleas may be responsible for the host switching of T. lewisi from their natural rodent species to primates. This and previous studies reporting T. lewisi in humans suggest that this trypanosome can cause sporadic and opportunistic flea-borne infection in primates.

The occurrence and ultrastructure of Trypanosoma (Herpetosoma) lewisi (Kent, 1880) Laveran and Mesnil, 1901, the parasite of rats (Rattus norvegicus) in Poland.

This study reports the light and electron microscopic examination of Trypanosoma (Herpetosoma) lewisi (Kent, 1880) Laveran and Mesnil, 1901, isolated from rats (Rattus norvegicus) from Poland. Bloodstream trypomastigotes were identified morphometrically from 100 specimens collected from three naturally infected rats Rattus norvegicus. Body length ranged from 15.45-23.64 microm and width from 1.3-2.32 microm while the free flagellum was 8.1 microm long. Electron microscopic study of bloodstream trypomastigotes exhibited typical ultrastructural features similar to those of other stercorarian trypanosomes. The presently determined morphological data have been compared with those provided by other authors.

Cell volume and DNA content of Trypanosoma lewisi and T. mega in vitro.

Two species of trypanosomes were harvested at a comparable stage in vitro development, just as cell division was ceasing and cell length had become maximal and its variability minimal. At this stage, T. mega displayed both a larger cell volume than T. lewisi (27.5 vs. 14.3 mu-2) and a greater DNA content (0.23 vs. 0.048 pg/cell).