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. Interestingly, captured colonies of T. infestans, the main vector of T. cruzi in the Southern Cone of South America, sporadically present with infection prevalence rates above 80%. Such high values are not consistent with the relatively short 7–8 week parasitemic period that has been reported in the literature. We experimentally measured the infectious periods of a group of T. cruzi-infected guinea pigs with two methods: xenodiagnosis and direct microscopy, each performed weekly for a year. Another group of infected guinea pigs received only direct microscopy weekly, 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.

Elucidating the mechanism ofTrypanosoma cruziacquisition by triatomine insects: evidence from a large field survey ofTriatoma infestans

“…A possible explanation for this finding is that newly infected mammalian hosts may undergo a rapid logistic increase in the number of circulating parasites. In other words, hosts may go from no parasitemia to a high level of infectiousness very quickly [12,13]. Vectors that feed on such hosts may be almost certain to acquire the parasite, regardless of the size of the blood meal they ingest.…”

Dispersal patterns of Trypanosoma cruzi in Arequipa, Peru

“…cruzi [5,[18][19][20][21][22][23][24]] -in addition to housing dogs and humans, which offer an abundance of blood meals for the vector and competent hosts for the parasite [5]. These data suggest that blocks remain free of T. cruzi due to either low rates of immigration or low probabilities of establishment as populations thrive once established.…”

“…Given the small sample size, T. cruzi introductions cannot be statistically correlated with the number of guinea pigs imported onto infected blocks. Hwoever, the high rate of inter-district guinea pig importation is likely to increase the probability of inter-district T. cruzi dispersal given that a single infected guinea pig can infect many vectors over its years-long lifetime [5,21,24]. The hypothesis that guinea pigs can infect many vectors is further supported because the number of guinea pigs is correlated with the density of T. infestans (S4 Fig), showing that the presence of guinea pigs helps support a large vector population which increases the number of potential T. cruzi vectors.…”

Trypanosoma cruzi Infection Does Not Decrease Survival or Reproduction of the Common Bed Bug, Cimex lectularius

“…Bed bug infection. At the beginning of each replicate, we collected unfed 1st instar C. lectularius individuals between 1 and 2 weeks old from the laboratory colony and fed each bug to engorgement on one of three 1-month-old mice infected with the T. cruzi strain Arequipa TC-35 19 (mouse infection details are presented in the following paragraphs). Between 40 and 100 bed bugs fed on each infected mouse once a week for 4 weeks, with one mouse per replicate to control for age and parasitemia, and three used in total throughout the entire experiment.…”

“…(We did not infect bugs using T. cruzi-infected guinea pigs because we have found in our prior work that T. cruzi-infected guinea pigs have highly variable infectiousness to triatomine bugs. 19 ) We used one individual guinea pig per treatment in each replicate for a total of six guinea pigs used across all replicates. Bugs from each group fed on a different individual to control for animal age.…”