The role of trans-sialidase on Trypanosoma cruzi parasite load in Rhodnius prolixus, impact of infection on triatomid behavior, and dispersal in a simulated field environment
Studies were undertaken to observe: (1) the role of trans -sialidase (TS) on Trypanosoma cruzi parasite load in Rhodnius prohius, (2) behavioral implications of T. cruzi infection in Rhodnius prolixus and (3) movement and attraction of laboratory R. prolixus within a simulated field environment.
Laboratory R. prolixus were infected with T. cruzi parasites (Silvio strain) with or without various TS types. The addition of Trypanosoma TS or any recombinant TS type did not consistently affect the parasite load. However, the addition of 1.0 μg TS monoclonal antibody/ml blood did significantly increase parasite load.
Fractionated T. cruzi subpopulations (Silvio strain), based on the phenotypic expression of TS, were fed to R. prolixus . Bugs ingesting parasites lacking TS expression (TS-parasites) produced significantly higher parasite loads than bugs ingesting either TS+ parasites (parasite phenotypically expressing TS) or unfractionated populations. Two other strains of T. cruzi (Tulahuen and Montalvania-13) were fractionated by TS phenotype and fed to bugs. Fractionated Tulahuen parasites only weakly produced differential parasite loads, the highest of which was produced by TS-parasites, but Montalvania-13 TS-parasites produced significantly larger parasite loads than either TS+ parasites or unfractionated parasites.
The feeding and defecation behavior of T. cruzi infected vs. uninfected insects were observed on an artificial membrane-feeding system, as well as on a live host (guinea pig) feeding system. Fifth instars were the best vectors, followed by adult females, 4th instars and finally, adult males. Bugs fasted for longer periods of time (5–6 months) took smaller blood meals but defecated significantly earlier than bugs fasted for shorter periods of time (2–3 months).
A field environment was simulated within a styrofoarn box. Movement of R. prolixus into various refuge types was observed. Fifth instars were more likely to seek a refuge than 3rd instars. Fed nymphs were more likely to seek a refuge than fasted nymphs. Potential bug attractants were tested within an olfactometers; ammonium hydroxide (NH4OH) was incorporated into refuges placed in the simulated field environment. Fasted fourth instars significantly preferred to rest in refuges containing NH4OH whereas fed third instars seemed to actively avoid refuges containing this chemical.