Effects of non-susceptible hosts on the infection with Trypanosoma cruzi of the vector Triatoma infestans: an experimental model.

We tested experimentally the effects of the presence of non-susceptible hosts on the infection with Trypanosoma cruzi of the vector Triatoma infestans. The experiment consisted in two treatments: with chickens, including two chickens (non-susceptible hosts) and two infected guinea pigs (susceptible hosts), and without chickens, including only two infected guinea pigs. The hosts were held unrestrained in individual metal cages inside a closed tulle chamber. A total of 200 uninfected T. infestans third instar nymphs were liberated in each replica, collected on day 14, and examined for infection and blood meal sources on day 32-36. The additional presence of chickens relative to infected guinea pigs: (a) significantly modified the spatial distribution of bugs; (b) increased significantly the likelihoods of having a detectable blood meal on any host and molting to the next instar; (c) did not affect the bugs' probability of death by predation; and (d) decreased significantly the overall percentage of T. infestans infected with T. cruzi. The bugs collected from inside or close to the guinea pigs' cages showed a higher infection rate (71-88%) than those collected from the chickens' cages (22-32%). Mixed blood meals on chickens and guinea pigs were detected in 12-21% of bugs. Although the presence of chickens would decrease the overall percentage of infected bugs in short term experiments, the high rate of host change of T. infestans would make this difference fade out if longer exposure times had been provided.

Biodiversity conservation: does phylogeny matter?

To conserve biodiversity, it is necessary not only to maximize the number of taxa that are saved today, but also to guarantee the maintenance of high levels of biological diversity in the future. A recent analysis argues that, to achieve this, consideration of phylogeny is essential.

Host-feeding patterns of domiciliary Triatoma infestans (Hemiptera: Reduviidae) in Northwest Argentina: seasonal and instar variation.

Blood meal sources of 1,964 Triatoma infestans Klug collected in bedrooms in 3 rural villages in northwest Argentina were identified by agar double-diffusion tests. Bugs were collected in September (1988, end of winter), October (1992), December (1988, spring), and March (1989, 1992, summer), and tested for human, dog, cat, chicken-duck, and goat-sheep serum antigens. From late winter to late summer, the percentage of domiciliary T. infestans that fed on humans decreased from 81 to 50-51%, whereas the percentage of bugs that fed on dogs rose from 39 to 45-57%, on chickens from 8 to 40-54%, and on cats from 7 to 12-23%. Bugs that fed on goat-sheep (2%) were collected mostly from 1 house. In winter, most bugs fed on humans only (48%), followed by dogs only (13%), cats only, or chickens only (approximately 1%). In spring-summer, the percentages of bugs that fed exclusively on humans (19%), dogs (16%), or chickens (17%) were similar. The seasonal shift was associated closely with changes in the sleeping places of people from indoors in winter to verandahs in summer, and with the presence of brooding hens or ducks in or close to bedrooms in spring-summer. In spring-summer, at each instar, bugs had more identified blood meals, switched hosts from earlier instars, fed on a larger number of different host types, and took mixed meals more frequently than in winter. Bugs collected from walls, roofs and household goods showed similar blood-feeding patterns, whereas bugs from beds showed the highest frequency of human meals. The increased anthropophagy of domiciliary T. infestans populations at the end of winter and during spring precedes or coincides with the spring peak incidence of acute cases of Chagas disease in the region. This is the 1st report documenting seasonal variation in host selection of any triatomine species.