Impact of community-based vector control on house infestation and Trypanosoma cruzi infection in Triatoma infestans, dogs and cats in the Argentine Chaco

Abstract

The relative impact of two community-based vector control strategies on house infestation by Triatoma infestans and Trypanosoma cruzi infection in bugs, domestic dogs and cats was assessed in two neighboring rural areas comprising 40 small villages and 323 houses in one of the regions most endemic for Chagas disease in northern Argentina. The prevalence and abundance of domestic infestation were 1.5- and 6.5-fold higher, respectively, in the area under pulsed, non-supervised control actions operating under the guidelines of the National Vector Control Program (NCVP) than in the area under sustained, supervised surveillance carried out jointly by the UBA research team and NCVP. The prevalence of infestation and infection varied widely among village groups within each area. In the pulsed control area, the prevalence of infection in bugs, dogs and cats was two- to three-fold higher than in the area under sustained surveillance, most of the infected animals qualified as autochthonous cases, and evidence of recent transmission was observed. Infection was highly aggregated at the household level and fell close to the 80/20 rule. Using multiple logistic regression analysis clustered by household, infection in dogs was associated positively and significantly with variables reflecting local exposure to infected T. infestans, thus demonstrating weak performance of the vector surveillance system. For high-risk areas in the Gran Chaco region, interruption of vector-mediated domestic transmission of T. cruzi requires residual insecticide spraying that is more intense, of a higher quality and sustained in time, combined with community participation and environmental management measures.

Fig. 1

A, Prevalence and abundance of Triatoma infestans and B, prevalence of Trypanosoma cruzi infection in Triatoma infestans, dogs and cats from two neighboring rural areas under different vector control strategies in Santiago del Estero, October 2002–July 2003. The mean abundance of bugs and (standard deviation) are shown beside squares (A). Numbers on top of bars are individuals infected/examined for infection (B).

Fig. 2

Age-specific prevalence of Trypanosoma cruzi infection in native dogs and cats from the area under pulsed control actions in Santiago del Estero, November 2002–July 2003. Numbers close to data points represent the numbers of animals examined for infection. Figure excludes seven dogs and three cats of unknown age.

Fig. 3

Age-specific prevalence of Trypanosoma cruzi infection in native dogs from two neighboring rural areas under different community-based vector control strategies in Santiago del Estero, November 2002–July 2003. Numbers close to data points represent the numbers of dogs examined for infection. Figure excludes 16 dogs of unknown age. Arrows indicate the main insecticide spraying campaigns. ^a Data taken from Cardinal et al. (2006a)

Fig. 4

Household distribution of Trypanosoma cruzi infection in Triatoma infestans, domestic dogs and cats from the area under pulsed vector control actions in Santiago del Estero, November 2002–July 2003. Numbers on top of bars are counts of households.