Heterogeneous infectiousness in guinea pigs experimentally infected with Trypanosoma cruzi

Abstract

Guinea pigs are important reservoirs of Trypanosoma cruzi, the causative parasite of Chagas disease, and in the Southern Cone of South America, transmission is mediated mainly by the vector Triatoma infestans. Interestingly, colonies of Triatoma infestans captured from guinea pig corrals sporadically have infection prevalence rates above 80%. Such high values are not consistent with the relatively short 7-8 week parasitemic period that has been reported for guinea pigs in the literature. We experimentally measured the infectious periods of a group of T. cruzi-infected guinea pigs by performing xenodiagnosis and direct microscopy each week for one year. Another group of infected guinea pigs received only direct microscopy to control for the effect that inoculation by triatomine saliva may have on parasitemia in the host. We observed infectious periods longer than those previously reported in a number of guinea pigs from both the xenodiagnosis and control groups. While some guinea pigs were infectious for a short time, other "super-shedders" were parasitemic up to 22 weeks after infection, and/or positive by xenodiagnosis for a year after infection. This heterogeneity in infectiousness has strong implications for T. cruzi transmission dynamics and control, as super-shedder guinea pigs may play a disproportionate role in pathogen spread.

Keywords: Cavia porcellus; Guinea pig; Infectiousness; Super-shedder; Triatoma infestans; Trypanosoma cruzi; Xenodiagnosis.

Figure 1

Patterns of infectiousness heterogeneity as assessed through infection of insects (xenodiagnosis) and parasite counts (microscopy) among eight guinea pigs (GP).

Figure 2

Parasitemia levels assessed by direct microscopy. Each line represents the trajectory of mean parasitemia from three capillary tubes of one animal. Disjoint lines represent weeks in which the parasitemia could not be evaluated. Parasitemia levels measured after week 22 were 0 for all animals and not shown in the graph.