Risk factors for domestic infestation by the Chagas disease vector, Triatoma dimidiata in Chiquimula, Guatemala

Spatial epidemiology and adaptive targeted sampling to manage the Chagas disease vector Triatoma dimidiata

Widespread application of insecticide remains the primary form of control for Chagas disease in Central America, despite only temporarily reducing domestic levels of the endemic vector Triatoma dimidiata and having little long-term impact. Recently, an approach emphasizing community feedback and housing improvements has been shown to yield lasting results. However, the additional resources and personnel required by such an intervention likely hinders its widespread adoption. One solution to this problem would be to target only a subset of houses in a community while still eliminating enough infestations to interrupt disease transfer. Here we develop a sequential sampling framework that adapts to information specific to a community as more houses are visited, thereby allowing us to efficiently find homes with domiciliary vectors while minimizing sampling bias. The method fits Bayesian geostatistical models to make spatially informed predictions, while gradually transitioning from prioritizing houses based on prediction uncertainty to targeting houses with a high risk of infestation. A key feature of the method is the use of a single exploration parameter, α, to control the rate of transition between these two design targets. In a simulation study using empirical data from five villages in southeastern Guatemala, we test our method using a range of values for α, and find it can consistently select fewer homes than random sampling, while still bringing the village infestation rate below a given threshold. We further find that when additional socioeconomic information is available, much larger savings are possible, but that meeting the target infestation rate is less consistent, particularly among the less exploratory strategies. Our results suggest new options for implementing long-term T. dimidiata control.

Effective public health interventions for the control and elimination of neglected tropical diseases require an efficient use of resources while still causing long-term disease reduction at the community level. To use resources to best effect, areas most in need of control efforts must be identified. However, strategies for correctly identifying these areas are rarely known due to the complex environmental, biological, and cultural factors shaping disease spread. In turn, incorrect prioritization of control targets can cause the intervention to have no lasting effect. We address this tradeoff between efficiency and efficacy by adapting control priorities throughout an intervention, targeting areas of high uncertainty during the initial stages while shifting to areas of greatest risk at later stages. In the context of controlling Triatoma dimidiata, the primary vector of Chagas disease in several countries in Latin America, our methods provide a means of targeting only a subset of homes for insecticide and housing improvements, while still reducing a village’s overall infestation rate below the critical threshold.

Risk factors and spatial analysis for domiciliary infestation with the Chagas disease vector Triatoma venosa in Colombia

Background:

In Colombia, communities living in the Andean region are the most affected by Chagas disease due to the presence of the main vectors, the environmental and risk factors associated with house infestation. Triatoma venosa is classified as a secondary vector that is frequently found in the departments of Boyaca and Cundinamarca, but epidemiological information and its association with risk factors in domestic and peridomestic areas is unknown. The study aimed to evaluate housing and environmental characteristics associated with domestic and peridomestic infestation by T. venosa and a risk map was estimated.

Methods:

A cross-sectional study was conducted in municipalities of Boyaca and Cundinamarca, Colombia. From March to July 2015, triatomine infestation screening surveys were conducted in 155 households. Multivariate analysis was performed to evaluate associations with the infestation and ecological niche modeling was estimated using environmental variables.

Results:

No statistical association was found with any of the housing variables in the adjusted multivariate analysis. However, in raw relationship infestation was associated with bushes  < 10 m (OR = 3; 95% CI: 1.3–7.3) and higher temperature p value  < 0.05. The developed final risk map pointed to 12 municipalities with no previous report of the disease, which should be sampled for the presence of T. venosa.

Conclusion:

This study highlights the relationship between environmental factors and T. venosa in Colombia and the importance of modeling tools to improve mapping efforts. Additional studies are needed to verify the association with bushes and higher temperatures and to verify infestation in predicted risk area with no previous report of the species

Risk factors for triatominae infestation in a municipality of Colombia

BACKGROUND

Identifying risk factors for Triatominae infestation is essential for the development of vector control interventions.

METHODS

To determine the intra- and peridomiciliary risk factors associated with triatomine infestation, a cross-sectional analytical study was carried out with random cluster sampling in two stages, which included the identification of risk factors by survey and direct observation, as well as the search and capture of triatomines. The detection of trypanosomes in triatomines was carried out by observing the rectal content and then by conventional polymerase chain reaction (PCR).

RESULTS

In 21 of the 207 houses inspected, 13 specimens of R. colombiensis and 19 specimens of P. geniculatus were found. Entomological indices included: dispersion 36%, infestation 10%, infection 65%, colonization 4.7%, density 15%, and concentration 152%. An association was found between the presence of Triatominae and the existence of branches and fissures in the floors, as well as with the presence of accumulated objects and with knowledge about Chagas disease. The risk of having triatomines in urban homes is 5.7 times higher than the risk in rural areas [confidence interval (CI) 0.508-67.567]; 6.6 times in houses with cracked soil (CI 0.555-81.994), 6 times in houses located near caneys (CI 0.820-44.781), and 6.16 times with accumulated objects (CI 1.542-39.238).

CONCLUSION

Chagas disease is a complex problem that requires control based on the vector's elimination or surveillance, which implies identifying species and their distribution, generating alerts, knowledge, and awareness in the population. It is necessary to intensify surveillance activities for the event, especially in changing aspects of Chagas diseases' transmission dynamics, such as urbanization and the type of housing associated with the vector's presence.

Novel Evolutionary Algorithm Identifies Interactions Driving Infestation of Triatoma dimidiata, a Chagas Disease Vector

Chagas disease is a lethal, neglected tropical disease. Unfortunately, aggressive insecticide-spraying campaigns have not been able to eliminate domestic infestation of Triatoma dimidiata, the native vector in Guatemala. To target interventions toward houses most at risk of infestation, comprehensive socioeconomic and entomologic surveys were conducted in two towns in Jutiapa, Guatemala. Given the exhaustively large search space associated with combinations of risk factors, traditional statistics are limited in their ability to discover risk factor interactions. Two recently developed statistical evolutionary algorithms, specifically designed to accommodate risk factor interactions and heterogeneity, were applied to this large combinatorial search space and used in tandem to identify sets of risk factor combinations associated with infestation. The optimal model includes 10 risk factors in what is known as a third-order disjunctive normal form (i.e., infested households have chicken coops AND deteriorated bedroom walls OR an accumulation of objects AND dirt floors AND total number of occupants ≥ 5 AND years of electricity ≥ 5 OR poor hygienic condition ratings AND adobe walls AND deteriorated walls AND dogs). Houses with dirt floors and deteriorated walls have been reported previously as risk factors and align well with factors currently targeted by Ecohealth interventions to minimize infestation. However, the tandem evolutionary algorithms also identified two new socioeconomic risk factors (i.e., households having many occupants and years of electricity ≥ 5). Identifying key risk factors may help with the development of new Ecohealth interventions and/or reduce the survey time needed to identify houses most at risk.

Implementation science: Epidemiology and feeding profiles of the Chagas vector Triatoma dimidiata prior to Ecohealth intervention for three locations in Central America

The Ecohealth strategy is a multidisciplinary data-driven approach used to improve the quality of people's lives in Chagas disease endemic areas, such as regions of Central America. Chagas is a vector-borne disease caused by the parasite Trypanosoma cruzi. In Central America, the main vector is Triatoma dimidiata. Because successful implementation of the Ecohealth approach reduced home infestation in Jutiapa department, Guatemala, it was scaled-up to three localities, one in each of three Central American countries (Texistepeque, El Salvador; San Marcos de la Sierra, Honduras and Olopa, Guatemala). As a basis for the house improvement phase of the Ecohealth program, we determined if the localities differ in the role of sylvatic, synanthropic and domestic animals in the Chagas transmission cycle by measuring entomological indices, blood meal sources and parasite infection from vectors collected in and around houses. The Polymerase Chain Reaction (PCR) with taxa specific primers to detect both, blood sources and parasite infection, was used to assess 71 T. dimidiata from Texistepeque, 84 from San Marcos de la Sierra and 568 from Olopa. Our results show that infestation (12.98%) and colonization (8.95%) indices were highest in Olopa; whereas T. cruzi prevalence was higher in Texistepeque and San Marcos de la Sierra (>40%) than Olopa (8%). The blood meal source profiles showed that in Olopa, opossum might be important in linking the sylvatic and domestic Chagas transmission cycle, whereas in San Marcos de la Sierra dogs play a major role in maintaining domestic transmission. For Texistepeque, bird was the major blood meal source followed by human. When examining the different life stages, we found that in Olopa, the proportion bugs infected with T. cruzi is higher in adults than nymphs. These findings highlight the importance of location-based recommendations for decreasing human-vector contact in the control of Chagas disease.

The resilience of Triatoma dimidiata: An analysis of reinfestation in the Nicaraguan Chagas disease vector control program (2010-2016)

Background

The control of Triatoma dimidiata, a major vector of Chagas disease, was believed to eliminate Trypanosoma cruzi transmission in Central America. This vector was known for its ability to repeatedly reinfest human dwellings even after initial insecticide spraying. Current vector control programs assume that community-based surveillance can maintain low levels of infestation over many years, despite a lack of evidence in the literature to corroborate this assumption. This study aims to evaluate long-term reinfestation risk in the Nicaraguan vector control program from 2010 to 2016.

Methods

We collected data from a cohort of 395 houses in Pueblo Nuevo, Nicaragua. Primary data were collected through a field survey to assess post-intervention levels of T. dimidiata house infestation in 2016, two years after the large-scale insecticide spraying. We obtained secondary data from the records about past infestation levels and control activities between 2010 and 2015. Multilevel mixed-effects logistic regression analyses were used to identify factors associated with post-intervention house infestation.

Results

The control program effectively reduced the infestation level from 2010 to 2014. Community-based surveillance was introduced in 2013; however, post-intervention infestation in 2016 had nearly reached pre-intervention levels in rural villages. Post-intervention house infestation was positively associated with poor wall construction, roofing tiles piled in the peri-domestic areas or the presence of dogs. Interestingly, the odds of post-intervention house infestation were one-fifth less when villagers sprayed their own houses regularly. Past infestation levels and the intensity of government-led insecticide spraying did not explain post-intervention house infestation.

Conclusions

The vector control program failed to offer sustained reductions in T. dimidiata house infestation. This experience would suggest that community-based surveillance is an insufficient approach to suppressing T. dimidiata house infestation over many years. This study provides evidence to suggest that control policies for T. dimidiata should be reconsidered throughout Central America.

Chagas Disease Infection among Migrants at the Mexico/Guatemala Border

Chagas disease results in the largest burden, in terms of disability-adjusted-life-years, of any parasitic disease in the Americas. Monitoring Chagas disease among migrants is critical to controlling its spread and to serving the needs of the migrant community. Therefore, we determined the prevalence and correlates of Chagas disease in regional and international migrant populations at the Mexico/Guatemala border. Data were collected as part of a larger study of human immunodeficiency virus (HIV) and migration. Participants were a sample of recent regional and international migrants who used an illicit substance or had recent problem drinking. Trypanosoma cruzi infection was classified as testing positive on two different enzyme-linked immunosorbent assays (ELISAs). Interviewer-administered surveys captured sociodemographics, migration history, Chagas disease knowledge, and access to care. We enrolled 389 recent migrants, and the prevalence of Chagas disease was 3.1%. Only 19% of the participants reported having ever heard of the disease and less than 1% had been previously tested. Trypanosoma cruzi-positive participants were more likely to have been born in a rural area or town than a city (92% yes versus 59% no, P = 0.02) and have recently lived in a house with a makeshift roof (33% yes versus 8% no, P < 0.01), walls (42% yes versus 13% no, P < 0.01), or floor (50% yes versus 21% no, P < 0.02), or cinderblock walls (92% yes versus 63% no, P = 0.04). With migration rapidly changing the distribution of Chagas disease, more work needs to be done to create targeted surveillance programs and provide access to affordable treatment among Latin American migrants.

Information to act: household characteristics are predictors of domestic infestation with the Chagas vector Triatoma dimidiata in Central America

The interruption of vectorial transmission of Chagas disease by Triatoma dimidiata in central America is a public health challenge that cannot be resolved by insecticide application alone. In this study, we collected information on previously known household risk factors for infestation in 11 villages and more than 2,000 houses in Guatemala, Honduras, and El Salvador, and we constructed multivariate models and used multimodel inference to evaluate their importance as predictors of infestation in the region. The models had moderate ability to predict infested houses (sensitivity, 0.32-0.54) and excellent ability to predict noninfested houses (specificity higher than 0.90). Predictive ability was improved by including random village effects and presence of signs of infestation (insect feces, eggs, and exuviae) as fixed effects. Multimodel inference results varied depending on factors included, but house wall materials (adobe, bajareque, and palopique) and signs of infestation were among the most important predictive factors. Reduced models were not supported suggesting that all factors contributed to predictions. Previous knowledge and information from this study show that we have evidence to prioritize rural households for improvement to prevent house infestation with Triatoma dimidiata in Central America. House improvement will most likely have other health co-benefits.

Factors associated with the occurrence of Triatoma sordida (Hemiptera: Reduviidae) in rural localities of Central-West Brazil

This study estimates the factors of artificial environments (houses and peridomestic areas) associated with Triatoma sordida occurrence. Manual searches for triatomines were performed in 136 domiciliary units (DUs) in two rural localities of Central-West Brazil. For each DU, 32 structural, 23 biotic and 28 management variables were obtained. Multiple logistic regression analysis was performed in order to identify statistically significant variables associated with occurrence of T. sordida in the study areas. A total of 1,057 specimens (99% in peridomiciles, mainly chicken coops) of T. sordida were collected from 63 DUs (infestation: 47%; density: ~8 specimens/DU; crowding: ~17 specimens/infested DU; colonisation: 81%). Only six (0.6%) out of 945 specimens examined were infected with Trypanosoma cruzi. The final adjusted logistic regression model indicated that the probability of T. sordida occurrence was higher in DU with wooden chicken coops, presence of > 30 animals in wooden corrals, presence of wood piles and presence of food storeroom. The results show the persistence of T. sordida in peridomestic habitats in rural localities of Central-West Brazil. However, the observed low intradomestic colonisation and minimal triatomine infection rates indicate that T. sordida has low potential to sustain high rates of T. cruzi transmission to residents of these localities.

Ecological, social and biological risk factors for continued Trypanosoma cruzi transmission by Triatoma dimidiata in Guatemala

Background

Chagas disease transmission by Triatoma dimidiata persists in Guatemala and elsewhere in Central America under undefined ecological, biological and social (eco-bio-social) conditions.

Methodology

Eco-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 Findings

Blood 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/Significance

Persistent 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.