House Reinfestation Research Articles

High prevalence of Trypanosoma rangeli and Trypanosoma cruzi in opossums and triatomids in a formerly-endemic area of Chagas disease in Southeast Brazil

In Brazil Trypanosoma rangeli has been detected in humans, sylvatic mammals and vectors in the Amazon Basin and in wild rodents in a Southern State. Here we report for the first time a high prevalence of T. rangeli in opossums and triatomids captured in peridomestic environments in a formerly-endemic area of Chagas disease in Southeast Brazil. Five molecular typing tools clearly indicate the presence of T. rangeli and Trypanosoma cruzi in mammalian reservoirs and triatomids. Twenty-one opossums ( Didelphis albiventris) were captured and flagellates were detected in the blood of 57.1% (12/21) of the animals. Single infections with T. rangeli or T. cruzi were diagnosed, respectively, in 58.4 and 8.3% of the opossums. Mixed infections were observed in 33.3%. Forty-four triatomids (38 Rhodnius neglectus and 6 Panstrongylus megistus) were collected in palm trees within 50 m from human dwellings. Flagellates were observed in the digestive tract and feces of 50% of the insects. PCR assays performed in DNA samples obtained from 16 cultures of the intestinal tract revealed single infection with T. cruzi (68.7%) or T. rangeli (6.3%), as well as mixed infections (25%). T. rangeli was also detected in the hemolymph of two specimens. Genotyping revealed predominance of T. cruzi I. The data suggest that R. neglectus in conjunction with D. albiventris may be significant factors in the maintenance of the sylvatic and peridomestic cycles of T. rangeli in the region. The finding of T. cruzi and T. rangeli in triatomine species capable of domiciliation and therefore considered as alternative vectors for the parasite transmission opens up the possibility of re-establishment of Chagas disease following reinfestation of houses.

Aspectos operacionais do controle do Triatoma brasiliensis

Vector control strategies against indigenous species is not easy, due to their capacity to reinvade treated premises from sylvatic ecotopes. Between August 1996 and December 1997 we conducted a study on reinfestation of houses after spraying in a county in the State of Ceará. Of 277 houses examined, 113 (40.8%) were infested (21.7% intradomiciliary and 35.4% peridomiciliary). Of the 433 Triatominae collected, 207 were Triatoma brasiliensis (49% of which intradomiciliary, with a mean of 1.8 insects/house) and 226 were Triatoma pseudomaculata (97% peridomiciliary). The age structure of the two indicated a univoltine development cycle for T. brasiliensis and two cycles per year for T. pseudomaculata. Four months after spraying with deltamethrin SC 25mg ia/m2, 9.7% of the houses were still positive, mainly with peridomestic infestations. Intradomiciliary wall bioassays showed persistence of the insecticide up to 9 months after spraying. Considering the high potential for recolonization of treated premises from sylvatic foci, we propose an operational strategy combining traditional evaluations and community-based surveillance with increased selective interventions and community education.

Monitoring house reinfestation by vectors of Chagas disease: a comparative trial of detection methods during a four-year follow-up

Domestic reinfestations by triatomine bugs were monitored after application of deltamethrin and apparent elimination of Triatoma infestans in Amamá and other nearby rural villages, north-west Argentina, from 1992 to 1996. The five methods used were sensor boxes, sheets of pink typing-paper, timed manual catches by a skilled three-person team aided by a flushing-out agent, collections by house-dwellers, and knockdown using insecticide fumigant canisters. In bedrooms, house-dwellers collected T. infestans significantly more frequently than the flushing-out method, but the reverse occurred in peridomestic sites. Both methods and sensor boxes revealed the frequent invasion of adult Triatoma guasayana and T. infestans, but neither T. guasayana nor Triatoma sordida colonized bedroom areas in spite of their rising abundance in nearby peridomestic sites. Sensor boxes were significantly more sensitive than the matched paper-sheets in three of five cross-sectional surveys. On average, each box recorded 2.0–3.2 times more triatomine fecal smears than each paper sheet. The frequency of dejecta in sensor boxes correlated positively with the proportion of houses where T. infestans, T. guasayana or T. sordida were captured by any method in bedroom areas. Triatomine fecal smears in sensor boxes were the earliest and most frequent sign of domiciliary infestation, followed by dwellers’ collections of adult bugs. Analyzing the data prospectively, we provide a quantitative, predictive understanding of detection methods and review the validity and interpretation of the different signs of infestation obtained. The most sensitive and cost-effective combination of detection methods for vector surveillance in domestic areas was the use of sensor boxes and house-dwellers collections.

La modificacion del biotopo perihabitacional en la profilaxis de la enfermedad de Chagas

In zones endemic for the American trypanosomiasis the modification of the biotopes surrounding human, rural, sylvatic or suburban housing, involves the arrangement of a clean perimetral area completely free of shrubs and chaparral, devoid of dens of wild animals and dwellings of domestic animals, to hinder the persistence of peridomestic foci where the proliferation of Triatomine bugs encourage the reinfestation of the human lodgings. The success of insecticide spraying campaigns, even with simultaneous amelioration of housing, are enhanced by the modification of the biotopes. A pilot field experience is presented; a 2 year active campaign in a suburban area of Villa Carlos Paz, province Cordoba, Argentina, confirming the methods to eliminate reinfestation of houses from peridomestic sites, in an area of low vector density.