Body size and hosts of Triatoma infestans populations affect the size of bloodmeal contents and female fecundity in rural northwestern Argentina.

Human sleeping quarters (domiciles) and chicken coops are key source habitats of Triatoma infestans-the principal vector of the infection that causes Chagas disease-in rural communities in northern Argentina. Here we investigated the links among individual bug bloodmeal contents (BMC, mg), female fecundity, body length (L, mm), host blood sources and habitats. We tested whether L, habitat and host blood conferred relative fitness advantages using generalized linear mixed-effects models and a multimodel inference approach with model averaging. The data analyzed include 769 late-stage triatomines collected in 120 sites from six habitats in 87 houses in Figueroa, Santiago del Estero, during austral spring. L correlated positively with other body-size surrogates and was modified by habitat type, bug stage and recent feeding. Bugs from chicken coops were significantly larger than pig-corral and kitchen bugs. The best-fitting model of log BMC included habitat, a recent feeding, bug stage, log Lc (mean-centered log L) and all two-way interactions including log Lc. Human- and chicken-fed bugs had significantly larger BMC than bugs fed on other hosts whereas goat-fed bugs ranked last, in consistency with average blood-feeding rates. Fecundity was maximal in chicken-fed bugs from chicken coops, submaximal in human- and pig-fed bugs, and minimal in goat-fed bugs. This study is the first to reveal the allometric effects of body-size surrogates on BMC and female fecundity in a large set of triatomine populations occupying multiple habitats, and discloses the links between body size, microsite temperatures and various fitness components that affect the risks of transmission of Trypanosoma cruzi.

Key source habitats and potential dispersal of triatoma infestans populations in Northwestern Argentina: implications for vector control.

BACKGROUND: Triatoma infestans -the principal vector of the infection that causes Chagas disease- defies elimination efforts in the Gran Chaco region. This study identifies the types of human-made or -used structures that are key sources of these bugs in the initial stages of house reinfestation after an insecticide spraying campaign. METHODOLOGY AND PRINCIPAL FINDINGS: We measured demographic and blood-feeding parameters at two geographic scales in 11 rural communities in Figueroa, northwest Argentina. Of 1,297 sites searched in spring, 279 (21.5%) were infested. Bug abundance per site and female fecundity differed significantly among habitat types (ecotopes) and were highly aggregated. Domiciles (human sleeping quarters) had maximum infestation prevalence (38.7%), human-feeding bugs and total egg production, with submaximal values for other demographic and blood-feeding attributes. Taken collectively peridomestic sites were three times more often infested than domiciles. Chicken coops had greater bug abundance, blood-feeding rates, engorgement status, and female fecundity than pig and goat corrals. The host-feeding patterns were spatially structured yet there was strong evidence of active dispersal of late-stage bugs between ecotopes. Two flight indices predicted that female fliers were more likely to originate from kitchens and domiciles, rejecting our initial hypothesis that goat and pig corrals would dominate. CONCLUSIONS AND SIGNIFICANCE: Chicken coops and domiciles were key source habitats fueling rapid house reinfestation. Focusing control efforts on ecotopes with human-fed bugs (domiciles, storerooms, goat corrals) would neither eliminate the substantial contributions to bug population growth from kitchens, chicken coops, and pig corrals nor stop dispersal of adult female bugs from kitchens. Rather, comprehensive control of the linked network of ecotopes is required to prevent feeding on humans, bug population growth, and bug dispersal simultaneously. Our study illustrates a demographic approach that may be applied to other regions and triatomine species for the design of innovative, improved vector control strategies.

Domestic animal hosts strongly influence human-feeding rates of the Chagas disease vector Triatoma infestans in Argentina.

BACKGROUND: The host species composition in a household and their relative availability affect the host-feeding choices of blood-sucking insects and parasite transmission risks. We investigated four hypotheses regarding factors that affect blood-feeding rates, proportion of human-fed bugs (human blood index), and daily human-feeding rates of Triatoma infestans, the main vector of Chagas disease. METHODS: A cross-sectional survey collected triatomines in human sleeping quarters (domiciles) of 49 of 270 rural houses in northwestern Argentina. We developed an improved way of estimating the human-feeding rate of domestic T. infestans populations. We fitted generalized linear mixed-effects models to a global model with six explanatory variables (chicken blood index, dog blood index, bug stage, numbers of human residents, bug abundance, and maximum temperature during the night preceding bug catch) and three response variables (daily blood-feeding rate, human blood index, and daily human-feeding rate). Coefficients were estimated via multimodel inference with model averaging. FINDINGS: Median blood-feeding intervals per late-stage bug were 4.1 days, with large variations among households. The main bloodmeal sources were humans (68%), chickens (22%), and dogs (9%). Blood-feeding rates decreased with increases in the chicken blood index. Both the human blood index and daily human-feeding rate decreased substantially with increasing proportions of chicken- or dog-fed bugs, or the presence of chickens indoors. Improved calculations estimated the mean daily human-feeding rate per late-stage bug at 0.231 (95% confidence interval, 0.157-0.305). CONCLUSIONS AND SIGNIFICANCE: Based on the changing availability of chickens in domiciles during spring-summer and the much larger infectivity of dogs compared with humans, we infer that the net effects of chickens in the presence of transmission-competent hosts may be more adequately described by zoopotentiation than by zooprophylaxis. Domestic animals in domiciles profoundly affect the host-feeding choices, human-vector contact rates and parasite transmission predicted by a model based on these estimates.

Spatial re-establishment dynamics of local populations of vectors of Chagas disease.

BACKGROUND: Prevention of Chagas disease depends mainly on control of the insect vectors that transmit infection. Unfortunately, the vectors have been resurgent in some areas. It is important to understand the dynamics of reinfestation where it occurs. Here we show how continuous- and discrete-time models fitted to patch-level infestation states can elucidate different aspects of re-establishment. Triatoma infestans, the main vector of Chagas disease, reinfested sites in three villages in northwest Argentina after community-wide insecticide spraying in October 1992. METHODOLOGY/PRINCIPAL FINDINGS: Different methods of estimating the probabilities of bug establishment on each site were compared. The results confirmed previous results showing a 6-month time lag between detection of a new infestation and dispersal events. The analysis showed that more new bug populations become established from May to November than from November to May. This seasonal increase in bug establishment coincides with a seasonal increase in dispersal distance. In the fitted models, the probability of new bug establishment increases with increasing time since last detected infestation. CONCLUSIONS/SIGNIFICANCE: These effects of season and previous infestation on bug establishment challenge our current understanding of T. infestans ecology and highlight important gaps in knowledge. Experiments necessary to close these gaps are discussed.

Sustainable vector control and management of Chagas disease in the Gran Chaco, Argentina.

Chagas disease remains a serious obstacle to health and economic development in Latin America, especially for the rural poor. We report the long-term effects of interventions in rural villages in northern Argentina during 1984-2006. Two community-wide campaigns of residual insecticide spraying immediately and strongly reduced domestic infestation and infection with Trypanosoma cruzi in Triatoma infestans bugs and dogs and more gradually reduced the seroprevalence of children <15 years of age. Because no effective surveillance and control actions followed the first campaign in 1985, transmission resurged in 2-3 years. Renewed interventions in 1992 followed by sustained, supervised, community-based vector control largely suppressed the reestablishment of domestic bug colonies and finally led to the interruption of local human T. cruzi transmission. Human incidence of infection was nearly an order of magnitude higher in peripheral rural areas under pulsed, unsupervised, community-based interventions, where human transmission became apparent in 2000. The sustained, supervised, community-based strategy nearly interrupted domestic transmission to dogs but did not eliminate T. infestans despite the absence of pyrethroid-insecticide resistance. T. infestans persisted in part because of the lack of major changes in housing construction and quality. Sustained community participation grew out of establishing a trusted relationship with the affected communities and the local schools. The process included health promotion and community mobilization, motivation, and supervision in close cooperation with locally nominated leaders.

Incidence of trypanosoma cruzi infection among children following domestic reinfestation after insecticide spraying in rural northwestern Argentina.

Following increasing reinfestation with Triatoma infestans after insecticide spraying, the household incidence of infection with Trypanosoma cruzi in children was positively related to the domestic abundance of infected T. infestans and the presence or proportion of infected dogs or cats in Amamá, a rural village in northwestern Argentina. Seven (12.1%) children seronegative for antibodies to T. cruzi at baseline, with no history of travel or blood transfusion, seroconverted after three years. Six incident cases lived in houses heavily infested with T. infestans, with high proportions of bugs infected with T. cruzi and having fed on humans or dogs. The remaining incident case occurred under a very light domestic infestation detected only at the endpoint, and most bugs had fed on humans. Dogs had a 17 times greater force of infection than children (4.3% per year). Sustained vector surveillance is crucially needed in high-risk areas for Chagas disease such as the Gran Chaco.

Congenital transmission of Trypanosoma cruzi infection in Argentina.

Trypanosoma cruzi, the causative agent of Chagas disease, infects 10-18 million people and may be transmitted to the newborn. Using various data sources, we estimated that nearly 850 congenital cases occurred in Argentina in 1993, or 6.3 expected cases per each reported case in 1994 and in 1994-2001. The congenital transmission of T. cruzi constitutes a sizeable public health problem in the region.

El papel del peridomicilio en la eliminacion de Triatoma infestants de comunidades rurales argentinas / The role of the peridomiciliary area in the elimination of Triatoma infestans in rural Argentine communities

El objetivo del estudio fue identificar el origen y estudiar la dinamica de la reinfestacion por Triatoma infestans ocurrida despues de rociar con deltametrina el domicilio y peridomicilio de 94 casas de tres comunidades rurales del noroeste argentino. La efectividad del rociamiento se evaluo inmediatamente despues y al segundo mes de rociar las viviendas. Ademas, se detectaron y rociaron 5 focos residuales peridomiciliarios y 3 preexistentes que no habian sido rociados.Para monitorizar la reinfestacion, se colocaron biosensores en los domicilios, se solicito a cada familia que capturase triatominos y los guardara en bolsas de plastico, y se buscaron triatominos en domicilios y peridomicilios usando un aereosol para desalojar a los insectos de sus refugios. Solo se realizaron rociamientos selectivos donde se encontro alguna colonia de T. infestns. Durante 30 meses de seguimiento, el porcentaje de casas donde se capturo algun T. infestans oscilo entre 3 por ciento y 9 por ciento. En 6 casas se capturaron T. infestans en mas de una evaluacion. El numero de peridomicilios infestados (19) fue el doble que el de domicilios (9). Solo se detectaron colonias de T. infestans en peridomicilios. La cifra de T. infestans capturados en peridomicilios fue seis veces mas alta que las de los domicilios. Las gallinas fueron el hospedador mas frecuente asociado con los focos peridomiciliarios. El peridomicilio constituyo el origen y la principal fuente de reinfestacion. Para reducir la velocidad de reinfestacion y la frecuencia de rociamientos es preciso combinar medidas de manejo ambiental y control quimico en los peridomicilios: reducir los refugios para triatominos; restringir la cria de aves a estructuras no colonizables por triatominos; aplicar un insecticida menos desagradable por agentes climaticos o realizar un segundo rociamiento de 6 a 12 meses despues del primero, y emplear un dispositivo para detectar tempranamente la presencia de T. infestans en peridomicilios

Se publica en ingles en el Bull. PAHO. Vol. 30(3), 1996