The course of infection in rats given small primary doses of Strongyloides ratti and S. venezuelensis

Abstract

Development of exact doses (<100) of Strongyloides venezuelensis third-stage larvae in adult Wistar rats was insignificant (mean proportion of 0·076 of the dose at day 8, n = 16) compared with a homogonic strain of S. ratti (0·538, n = 6; 0·726, n = 6) and heterogonic S. ratti (0·681, n = 6). Newly-weaned Wistars allowed development of a mean proportion of S. venezuelensis of 0·298 (n = 4) compared with 0·013 (n = 4) of the same sample of larvae in adult hosts. Experiments with 75Se-labelled larvae established that S. venezuelensis effectively failed to migrate from skin to intestine in adult animals, while mean proportions of 0·141 (n = 5) and 0·138 (n = 4) of the label was found in the intestines of newly-weaned rats 72 h after skin application. Labelled larvae of homogonic S. ratti migrated equally well in both age groups of host (0·350 and 0·358 in 12- and 3-week-olds respectively). Adult S. venezuelensis transferred surgically to the intestines of previously uninfected full-grown Wistars survived over a 21-day period to the same extent as either strain of S. ratti. Resistance of Wistar rats to S. venezuelensis therefore appears to affect the migratory stage preferentially. S. venezuelensis developed better in mature PVG inbred rats (mean = 0·301, n = 20). Studies of S. ratti showed that infections of both strains initiated by exact (<100) doses in Wistar rats had decayed to insignificance between days 26 and 32. The rate of loss of adults of the heterogonic strain was significantly greater than that for the homogonic. The egg content of worms declined as infection progressed and rats were idiosyncratic in their influence on parasite reproduction from the earliest time of sampling (8 d). It was established that ‘autoinfection’ was an unlikely feature of the biology of homogonic S. ratti following the surgical transfer of 450 first-stage larvae to the intestines of 8 adult Wistar rats. No evidence of infection appeared in the guts of these animals 8 days post-transfer. The significance of these results in terms of the biology of Strongyloides spp. naturally occurring in the rat is discussed.

Density-dependent immune responses against the gastrointestinal nematode Strongyloides ratti

“…S. ratti is a gastrointestinal nematode parasite of the rat. Infections in rats are typically acute, being completely cleared after approximately 30 days (Carter and Wilson, 1989), though low level, longer lived infections also occur (Kimura et al, 1999). Hosts become infected when infective third stage larvae penetrate the skin of their host and migrate via the cranium and nasal-frontal region (Koga et al, 1999; Tindall and Wilson, 1988), to the gut, where they moult via a fourth larval stage into adult females only, which reproduce by parthenogenesis (Viney, 1994).…”

Effects of in vitro culture methods on morphological development and infectivity of Strongyloides venezuelensis filariform larvae

“…The morphology of L 3 obtained from different conventional in vitro cultures as well as those of the in vivo derived adult worms have been reported previously (Little, 1966;Hasegawa et al, 1988;Taira et al, 1994). After primary infection with S. venezuelensis, the subsequent development to the parasitic adult stage in a single and/or concurrent infections with S. ratti, pulmonary and intestinal worm burdens, kinetics of egg outputs, persistence of infection and immunological responses have been reported in rats (Werthiem, 1970a(Werthiem, , 1970bCarter and Wilson, 1989), mice (Sato and Toma, 1990), Mongolian gerbils (Tsuji et al, 1993) and Syrian golden hamsters (Shi et al, 1994). In the present study, we have demonstrated that in vitro culture methods have significant effects on morphological development to the L 3 stage, however, they do not influence the infectivity of the larvae to rats.…”

“…Eggs, L 3 and adults of S. venezuelensis obtained from experimentally infected rats can survive for an extended period in various culture media at different temperatures. The development of intestinal nematode from the free-living stage (e.g., L 3 stage) to the parasitic adult stage depends on several factors related to host (e.g., species, strain, age, sex and resistance) and parasite species (e.g., strain, infective dose and culture age of L 3 ) (Solomon and Haley, 1966;Carter and Wilson, 1989;Sato and Toma, 1990;Khan et al, 1993). Taira et al (1994) have demonstrated that the inoculation routes of S. venezuelensis L 3 significantly influence the worm burdens.…”

Migration of Strongyloides venezuelensis in Rats after Oral Inoculation of Free-Living Infective Larvae

“…The intracorporal migration route of SVZ from the stomach to the liver and then through the blood stream to lung was verified by the data reported here. The key parameters included the body length of migrating worms, the time of their first appearance and disappearance of MLS in each target organ and the establishment of fecundity after oral inoculation [6]. Carter and Wilson [6] reported that SVZ failed to migrate from the skin to intestine in adult Wistar rats, the number of eggs in the uterus declined as the infection progressed and rats were idiosyncratic in their influence on parasite reproduction from the earliest time of sampling.…”

“…The key parameters included the body length of migrating worms, the time of their first appearance and disappearance of MLS in each target organ and the establishment of fecundity after oral inoculation [6]. Carter and Wilson [6] reported that SVZ failed to migrate from the skin to intestine in adult Wistar rats, the number of eggs in the uterus declined as the infection progressed and rats were idiosyncratic in their influence on parasite reproduction from the earliest time of sampling. In the Mongolian gerbil, the fecal egg output and fecundity of the worm remain relatively stable over a long period [4].…”