House improvements and community participation in the control of Triatoma dimidiata re-infestation in Jutiapa, GuatemalaMelhorias habitacionais com participação comunitária no controle da re-infestação por Triatoma dimidiata em Jutiapa, Guatemala

BackgroundChagas disease transmission by Triatoma dimidiata persists in Guatemala and elsewhere in Central America under undefined ecological, biological and social (eco-bio-social) conditions.MethodologyEco-bio-social risk factors associated with persistent domiciliary infestation were identified by a cross-sectional survey and qualitative participatory methods. Quantitative and qualitative data were generated regarding Trypanosoma cruzi reservoirs and triatomine hosts. Blood meal analysis and infection of insects, dogs and rodents were determined. Based on these data, multimodel inference was used to identify risk factors for domestic infestation with the greatest relative importance (>0.75).Principal FindingsBlood meal analysis showed that 64% of 36 bugs fed on chickens, 50% on humans, 17% on dogs; 24% of 34 bugs fed on Rattus rattus and 21% on Mus musculus. Seroprevalence among 80 dogs was 37%. Eight (17%) of 46 M. musculus and three (43%) of seven R. rattus from households with infected triatomines were infected with T. cruzi Distinct Typing Unit I. Results from interviews and participatory meetings indicated that vector control personnel and some householders perceived chickens roosting and laying eggs in the house as bug infestation risk factors. House construction practices were seen as a risk factor for bug and rodent infestation, with rodents being perceived as a pest by study participants. Multimodel inference showed that house infestation risk factors of high relative importance are dog density, mouse presence, interior wall plaster condition, dirt floor, tile roofing and coffee tree presence.Conclusions/SignificancePersistent house infestation is closely related to eco-bio-social factors that maintain productive T. dimidiata habitats associated with dogs, chickens and rodents. Triatomine, dog and rodent infections indicate active T. cruzi transmission. Integrated vector control methods should include actions that consider the role of peridomestic animals in transmission and community memberś level of knowledge, attitudes and practices associated with the disease and transmission process.

Seventeen variables were evaluated as possible risk factors for the intradomiciliary infestation with Triatoma dimidiata in 644 houses in Jutiapa, Guatemala. During 2004 the houses were assessed for vector presence and evaluated for hygiene, cluttering, material comfort, construction conditions and number of inhabitants, among other factors. Chi-square analysis detected significant associations between vector presence and eight variables related to domestic sanitary and construction conditions. Log-linear models showed that regardless of the age of the house, the odds of vector presence were 4.3 and 10 times lower in houses with a good socioeconomic status compared with poor and very poor houses respectively. Log-linear models also pointed to a greater chance of vector presence when walls lacked plastering (3.85 times) or walls had low quality-incomplete plastering (4.56 times), compared with walls that were completely plastered. Control strategies against T. dimidiata should include the introduction of better-quality but inexpensive plastering formulations and better sanitation practices should also be promoted among the population. Such control strategies should not only reduce or eliminate infestation, but also prevent vector reinfestation.

Eight Triatoma dimidiata populations from different geographic regions were compared along with related species using traditional morphometry of head characters. A method for removing allometric change was used for the intraspecific comparisons, and scaling for the isometric change of size was used for the interspecific comparisons. The intraspecific comparison showed significant head shape differences between T. dimidiata populations correlating with geography, showing a separation between the northern, intermediate, and southern collections (more evident in females), and supporting the idea that this species includes several evolutionarily divergent populations. The positioning of one sylvatic group from Guatemala did not correlate with geography, because it was more closely related to a distinct population of Colombia. This sylvatic group was found in caves, while the Colombian specimens, although collected in houses, may have migrated from nearby caves. Evolutionary and/or ecological influences could be responsible for the head shape similarities between these two groups: a common ancestral origin of both populations or a morphological convergence caused by similar environmental pressures. The interspecific comparisons included four other regional species of the same genus, three of them belonging to the phyllosoma complex (T. pallidipennis, T. mexicana, and T. ryckmani, the latter provisionally) and the fourth one classified in the protracta complex (T. nitida). Both complexes were readily separated by their head dimensions, even after size adjustment, and our data support inclusion of T. dimidiata within the phyllosoma complex.

Abstract. A novel method using vector blood meal sources to assess the impact of control efforts on the risk of transmission of Chagas disease was tested in the village of El Tule, Jutiapa, Guatemala. Control used Ecohealth interventions, where villagers ameliorated the factors identified as most important for transmission. First, after an initial insecticide application, house walls were plastered. Later, bedroom floors were improved and domestic animals were moved outdoors. Only vector blood meal sources revealed the success of the first interventions: human blood meals declined from 38% to 3% after insecticide application and wall plastering. Following all interventions both vector blood meal sources and entomological indices revealed the reduction in transmission risk. These results indicate that vector blood meals may reveal effects of control efforts early on, effects that may not be apparent using traditional entomological indices, and provide further support for the Ecohealth approach to Chagas control in Guatemala.

Abstract. Infection rate is an estimate of the prevalence of arbovirus infection in a mosquito population. It is assumed that when infection rate increases, the risk of arbovirus transmission to humans and animals also increases. We examined some of the factors that can invalidate this assumption. First, we used a model to illustrate how the proportion of mosquitoes capable of virus transmission, or infectious, is not a constant fraction of the number of infected mosquitoes. Thus, infection rate is not always a straightforward indicator of risk. Second, we used a model that simulated the process of mosquito sampling, pooling, and virus testing and found that mosquito infection rates commonly underestimate the prevalence of arbovirus infection in a mosquito population. Infection rate should always be used in conjunction with other surveillance indicators (mosquito population size, age structure, weather) and historical baseline data when assessing the risk of arbovirus transmission.

Dispersion and invasion capacity of sylvatic populations of Triatoma dimidiata (Latreille) were investigated during 14 mo by means of experimental chicken coops installed in a nature reserve within the Maya Biosphere, Petén, Guatemala. In addition, palm trees, underground archeological holes (chultunes) and piles of limestones within the forest were inspected as potential sylvatic habitats of T. dimidiata. From the three types of sylvatic habitats we inspected, all served as shelter and breeding sites for T dimidiata. The natural infection of these bugs (n = 72) with Trypanosoma cruzi (Chagas) was high (25%) and represent a risk for humans who colonize the forest. T. dimidiata quickly invaded the experimental chicken coops installed in the primary forest, albeit at very low densities. However, only one adult bug was encountered in the chicken coops installed in a secondary forest. Dispersal of adult T. dimidiata was most apparent at the end of the dry season. Overall, our results indicate a potential risk for invasion by sylvatic T. dimidiata of domestic environments in this area, with a risk of T. cruzi transmission to humans. We suggest that a system of community-based surveillance should be developed to detect new infestations and organize prompt treatment of any new cases of acute Chagas disease that may result.

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