A prospective study of the effects of sustained vector surveillance following community-wide insecticide application on Trypanosoma cruzi infection of dogs and cats in rural Northwestern Argentina.

Domestic dogs were used as natural sentinels to assess prospectively the long-term impact of selective, community-based spraying with pyrethroid insecticides after community-wide spraying on transmission of Trypanosoma cruzi in rural villages under surveillance between 1992 and 2002. In 2000 and 2002 light infestations by Triatoma infestans were recorded, and 523 dogs and cats were examined serologically or by xenodiagnosis. The prevalence of T. cruzi infection in dogs decreased from 65% at baseline to 8.9% and 4.7% at 7.5 and 10 years after sustained vector surveillance, respectively. The average annual force of infection dropped 260-fold from 72.7 per 100 dog-years at baseline to <0.3% in 2002, as determined prospectively and retrospectively from the age-prevalence curve of native dogs born during surveillance. Multiple logistic regression analysis showed that prevalent cases in dogs in 2000 and 2002 were associated positively and significantly with the peak number of T. infestans caught in domestic areas at the dog's compound during its lifetime. The sustained decline in T. cruzi infections in dogs and cats is the result of selective, community-based insecticide spraying that kept the abundance of infected T. infestans at marginal levels, fast host population turnover, and low immigration rates from areas with active transmission.

Trypanosoma cruzi infection in Triatoma infestans and other triatomines: long-term effects of a control program in rural northwestern Argentina / Infección por Trypanosoma cruzi en Triatoma infestans y otros triatómidos: efectos a largo plazo de un programa de control en una zona rural del noroeste de Argentina

The prevalence of Trypanosoma cruzi infection in Triatoma infestans, Triatoma guasayana, and Triatoma sordida was evaluated in Amamá and other neighboring rural villages in northwestern Argentina for five years after massive spraying with deltamethrin in 1992 and selective sprays thereafter. Local residents and expert staff collected triatomines in domiciliary and peridomestic sites. During 1993-1997, the prevalence of T.cruzi was 2.4 per cent in 664 T. infestans, 0,7 per cent in 268 T.guasayana, and 0.2 per cent in 832 T.sordida. T.cruzi infection was more frequently detected in adult bugs and in triatomines collected at domiciliary sites. The infected T.guasayana and T.sordida were nymphs and adults, respectively, captured at peridomestic sites. The prevalence of T.cruzi infection in T.infestans decreased from 7.7 per cent to 1.5 per cent during the surveillance period, although that change was not statistically significant. Comparison of T.infestans infection rates before the control program and during surveillance showed a highly significant decrease from 49 per cent to 4.6 per cent in bedrooms, as well as a fall from 6 per cent to 1.8 per cent in peridomestic sites. Because of its infection with T.cruzi and frequent invasion of domiciliary areas and attacks on humans and dogs, T. guasayana appeared implicated as a putative secondary vector of T.cruzi in domestic and peridomestic sites during the surveillance period.T. sordida was the most abundat species, but it was strongly associated with chickens and showed little tendency to invade bedrooms

Durante los cinco años posteriores a una fumigación masiva con deltametrina realizada en 1992 y seguida de fumigaciones selectivas, se investigó la prevalencia de la infección por Trypanosoma cruzi en Triatoma infestans, Triatoma guasayana y Triatoma sordida en Amamá y otras poblaciones rurales vecinas del noroeste de Argentina. Los triatómidos fueron recogidos en los domicilios y en el área peridoméstica por los propios residentes y por personal experto. Durante el quinquenio 1993­1997, la prevalencia de T. cruzi fue de 2,4% en 664 T. infestans, de 0,7% en 268 T. guasayana y de 0,2% en 832 T. sordida. La infección por T. cruzi se detectó con mayor frecuencia en las chinches adultas y en los triatómidos recogidos en los domicilios. T. guasayana y T. sordida fueron, respectivamente, ninfas y adultos recogidos en el área peridoméstica. Durante el período de vigilancia, la prevalencia de la infección por T. cruzi en T. infestans disminuyó de 7,7% en 1993 a 1,5% en 1997, aunque este cambio no fue estadísticamente significativo. La comparación de las tasas de infección de T. infestans antes del programa de control (1992) y durante el período de vigilancia (1993­1997) reveló una disminución altamente significativa, de 49% a 4,6%, en los dormitorios y también en las áreas peridomésticas (de 6% a 1,8%). Debido a su infección por T. cruzi y a su frecuente invasión de las áreas domésticas con ataques a los humanos y a los perros, T. guasayana parecía estar implicado como vector secundario de T. cruzi en las áreas domésticas y peridomésticas durante el período de vigilancia. T. sordida fue la especie más abundante, pero estaba estrechamente asociada a los pollos y mostró escasa tendencia a invadir los dormitorios