Shifting host choices of the vector of Chagas disease, <em>Triatoma infestans</em>, in relation to the availability of hosts in houses in north-west Argentina.

1. Data from a 4-year study on the blood meal sources of 1964 specimens of Triatoma infestans collected from human sleeping places in three rural villages of north-west Argentina were analysed using individual houses as the basic sampling unit. Logistic multiple regression analysis was used to test whether the proportion of domiciliary T. infestans that fed on humans dogs chickens or cats was related to the number of these hosts in the house and to vector density. 2. On `average, dogs were 2.6 or 2.3 times more likely to lie selected than humans relative to availability, in summer 1992 (at 23 houses) or spring-summer 1988 89 (at 11 houses). respectively, but (0.8 less likely to be selected than humans, relative to their availability in winter 1988 (at 12 houses). In the hot season, chickens were 48 times more likely to be selected than humans relative to their assumed availability 3. From data collected during the hot season, the proportion of bugs that fed on humans among all bugs with any identified blood source (the human blood index. HBI). or on humans only HBI ONLY). decreased significantly as both the number of dogs sharing human sleeping places (room-mate dogs) and the proportion of bugs that fed on chickens increased. The proportion of bugs that fed partly on dogs and dogs alone, increased significantly with increasing numbers of room-mate dogs and decreased significantly with an increasing proportion of bugs feeding on chickens. 4. From data collected during the winter when fewer cases of feeding on chickens were detected and most people slept indoors, both HBI and HBI ONLY increased significantly with the number of humans and decreased with the number of room-mute dogs. 5. The effects of vector density on HBI or HBI ONLY were investigated by multiple logistic regression analysis. In summer 1992. after a backward elimination procedure. both HBI and HBI ONLY were significantly and negatively related to the density of domiciliary T. infestans per house, the number of room-mate dogs and the proportion of the bugs that fed on chickens A marginally significant and negative relationship between H Bl and the log-density of bugs was verified in two published datasets. 6. Analysis of 13 published host-feeding patterns of domiciliary T. infestans and of another 27 datasets from 11 other triatomine species collected inside or around bedroom areas. showed that HBI was inversely and significantly related to the proportion of bugs that fed on chickens (in both groups of vector species) or on dogs (for T. infestans). 7. Our study is the first to show that: (i) the likelihood of feeding partly on humans, or on humans only. significantly decreased in the presence of dogs and chickens in bedroom areas: (ii) the HBI was also negatively related to the density of hugs per house alter controlling for the effects of chickens and room-male dogs: and (iii) the likelihood of feeding on dogs increased significantly with more room-mate dogs and decreased width an increasing proportion of hugs feeding on chickens. Some epidemiological consequences of these relationships for transmission, control, zoo- prophylaxis and modelling are discussed. [ABSTRACT FROM AUTHOR]