The different infectivity of Trichinella spiralis and Trichinella nativa in rat does not solely localize to enteral or parenteral phase.

Rats are selective hosts for Trichinella nativa; infection levels in their muscles remain low when compared to Trichinella spiralis. To identify in which phase of the life cycle the selective responses take place, rats were infected perorally (p.o.) and intravenously (i.v.) with T. spiralis and T. nativa. Six rats were placed in each group; three rats served as uninfected controls. The infection intensities were examined 5 or 6 weeks after the infection. T. spiralis muscle larva burden was 57 times higher compared to that of T. nativa after p.o. inoculation (mean larvae per gram ± SD, 1,243 ± 378.9 vs. 22 ± 21.5). In i.v. inoculation, 12 times more T. spiralis larvae reached the muscle than with T. nativa. Also, in vitro newborn larva (NBL) production at day 6 postinfection was analyzed for parasites originating from both rat and mouse. The mean number of in vitro-produced NBL of rat-origin T. spiralis during 24 h was 70 (95 % CI, 65-75) and of T. nativa, 23 (95 % CI, 21-24). Intriguingly, this difference was less obvious with mouse-origin female Trichinella. NBL production of mouse origin T. spiralis was 57 (95 % CI, 51-62) and T. nativa, 29 (95 % CI, 26-31). Intestine histology at day 40 post p.o. infection, serological response, and weight dynamics were indistinguishable between the Trichinella species but differed from controls. Our results show that the defense against T. nativa is not solely enteral in rats but may partly be explained by different reproduction processes for the two Trichinella species in rat.