Evaluation of risk factors for rural infestation by Triatoma pallidipennis (Hemiptera: Triatominae), a Mexican vector of Chagas disease

Thinking green: Insecticidal effect of biorational solutions against Triatoma pallidipennis Stal (Hemiptera: Triatominae)

The control of triatomine vectors depends almost exclusively on conventional insecticides. These compounds can, nevertheless, cause negative effects on environmental and human health as well as induce resistance in triatomines. Therefore, we need to look for more sustainable alternatives. Triatoma pallidipennis is one of the main chagasic vectors in Mexico. We evaluated the insecticidal effectiveness of two oils (neem and cinnamon), and two desiccants (potassium salts of fatty acids and diatomaceous earth), on 3rd instar nymphs of T. pallidipennis. The laboratory test involved direct exposure of the treatments to the insects. We found that diatomaceous earths caused 80 % mortality of nymphs after 30 days. Meanwhile, the cumulative mortality for the other treatments did not exceed 50 %. When applied to inert surfaces, the powder formulation of diatomaceous earth demonstrated greater effectiveness than the aqueous suspension. Thus, diatomaceous earth could be a promising alternative for an environmentally friendly control of triatomines.

Triatoma pallidipennis (Stål, 1872) (Hemiptera: Reduviidae) and its potential for infestation in Tecozautla, Hidalgo state, Mexico

Triatoma pallidipennis is an exclusive and widely distributed species in Mexico and one of the three main vectors that transmit Chagas disease in the country. The state of Hidalgo is an endemic area for Chagas disease where the presence of several species of triatomines has been reported. The objective of our work was to describe the morphology, colonization process, and reproductive behavior of T. pallidipennis in Guadalupe, Tecozautla, two years after the first collection of a specimen in this region. A total of 28 specimens was collected at both domicile and peridomicile, showing a 17.8% infection rate. The main collection site was a woodshed, and despite the collection of adults in the dwelling, we did not find eggs, exuviae, or nymphs. One female monitored from collection day until death laid 566 eggs, with a hatching rate of 95%, showing an increase of oviposition when cohabited with a male. The results showed the capacity that T. pallidipennis has to infest areas (mainly human dwellings) when it settles down, which would imply a risk for the population that lives in the locality.

Acute toxicity of two insecticides on two species of Chagas disease vectors

The control of triatomine vectors of Chagas disease is mainly based on the use of pyrethroid insecticides. Because chemical control is the primary method for managing these insects, it is crucial to diversify the range of products utilized to mitigate the risk of resistance development. This study evaluated the toxicity of two insecticides with different modes of action on Triatoma dimidiata Latreille and T. pallidipennis Stal first and third instar nymphs. Our study focused on the effects of two insecticides, buprofezin (a growth regulator) and flunocamid (an anti-feeder), on the mortality rate of triatomine bugs in a laboratory setting. Moreover, we investigated how direct and indirect (film method) exposure to these insecticides impacted the survival of the insects. Flonicamid emerged as a promising insecticide for triatomine control since it caused 100% mortality in first-instar nymphs 48 h after direct exposure. While, in third instar nymphs, the maximum mortality was 88% at 72 h after exposure. Our result can be used as a basis for future triatomine control plans.

Influence of blood meal source on the biological parameters of Triatoma pallidipennis (Heteroptera: Reduviidae) from Mexico

Chagas disease is one of the most important vector-borne diseases in Latin America, including Mexico. Triatoma pallidipennis (Stål) (Hemiptera: Reduviidae) is a Mexican triatomine vector commonly associated with different hosts. The influence of six blood meals (rabbits, rats, mice, dogs, cats and chickens) on six biological parameters of the biology of T. pallidipennis was evaluated. A significant difference was found in the period of egg-to-adult development between the five mammalian feeds (mean 195 days) and the chicken feed (221 days). The probability of survival was significantly lower in the chicken cohort (0.285). The total number of blood meals to moult from the first instar to the adult stage was the highest in the chicken cohort (10-15). This cohort had the significantly highest rate of females at the end cycle. The mean number of eggs laid per female and the egg eclosion rate were similar among the six food sources. Most results seemed to be influenced by the higher nutritional quality of the mammalian blood compared to the bird's blood and the increased energy expenditure required for the digestion of bird blood. These results clearly show that T. pallidipennis, unlike other triatomine species, has a high reproductive capacity when feeding on different hosts.

Trypanosoma cruzi transmission dynamics in a synanthropic and domesticated host community

Trypanosoma cruzi is the causative agent of Chagas disease, a Neglected Tropical Disease affecting 8 million people in the Americas. Triatomine hematophagous vectors feed on a high diversity of vertebrate species that can be reservoirs or dead-end hosts, such as avian species refractory to T. cruzi. To understand its transmission dynamics in synanthropic and domesticated species living within villages is essential to quantify disease risk and assess the potential of zooprophylaxis. We developed a SI model of T. cruzi transmission in a multi-host community where vector reproduction and parasite transmission depend on a triatomine blood-feeding rate accounting for vector host preferences and interference while feeding. The model was parameterized to describe T. cruzi transmission in villages of the Yucatan peninsula, Mexico, using the information about Triatoma dimidiata vectors and host populations accumulated over the past 15 years. Extensive analyses of the model showed that dogs are key reservoirs and contributors to human infection, as compared to synanthropic rodents and cats, while chickens or other domesticated avian hosts dilute T. cruzi transmission despite increasing vector abundance. In this context, reducing the number of dogs or increasing avian hosts abundance decreases incidence in humans by up to 56% and 39%, respectively, while combining such changes reduces incidence by 71%. Although such effects are only reached over >10-years periods, they represent important considerations to be included in the design of cost-effective Integrated Vector Management. The concomitant reduction in T. cruzi vector prevalence estimated by simulating these zooprophylactic interventions could indeed complement the removal of colonies from the peridomiciles or the use of insect screens that lower vector indoor abundance by ~60% and ~80%. These new findings reinforce the idea that education and community empowerment to reduce basic risk factors is a cornerstone to reach and sustain the key objective of interrupting Chagas disease intra-domiciliary transmission.

Inequalities in the social determinants of health and Chagas disease transmission risk in indigenous and creole households in the Argentine Chaco

Background

The social determinants of health (SDHs) condition disease distribution and the ways they are handled. Socio-economic inequalities are closely linked to the occurrence of neglected tropical diseases, but empirical support is limited in the case of Chagas disease, caused by the protozoan Trypanosoma cruzi. Herein we assessed the relationship between key structural SDHs and the risk of T. cruzi vector-borne transmission in rural communities of the Argentine Chaco occupied by creoles and an indigenous group (Qom). We used multiple correspondence analysis to quantify the household-level socio-economic position (social vulnerability and assets indices), access to health and sanitation services, and domestic host availability. We identified the most vulnerable population subgroups by comparing their demographic profiles, mobility patterns and distribution of these summary indices, then assessed their spatial correlation and household-level effects on vector domiciliary indices as transmission risk surrogates.

Results

Qom households had higher social vulnerability and fewer assets than creoles, as did local movers and migrant households compared with non-movers. We found significantly positive effects of social vulnerability and domestic host availability on infected Triatoma infestans abundance, after adjusting for ethnicity. Access to health and sanitation services had no effect on transmission risk. Only social vulnerability displayed significant global spatial autocorrelation up to 1 km. A hotspot of infected vectors overlapped with an aggregation of most vulnerable households.

Conclusions

This synthetic approach to assess socio-economic related inequalities in transmission risk provides key information to guide targeted vector control actions, case detection and treatment of Chagas disease, towards sustainability of interventions and greater reduction of health inequalities.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3444-5) contains supplementary material, which is available to authorized users.

Biological parameters of the triatomine, Meccus phyllosomus pallidipennis, fed on two bloodmeal sources under laboratory conditions

Chagas disease is one of the most important vector-borne diseases in Latin America, including Mexico. Meccus phyllosomus pallidipennis (Stål), 1872 (Hemiptera: Reduviidae) is a Mexican triatomine vector that is commonly associated with hens and rabbits. The biological parameters of two cohorts fed on hens (H) and on rabbits (R) were evaluated. The median lifecycles of the two cohorts were 198 days (H) and 180 days (R). Moreover, mortality was around 30% in both cohorts. Time lapse for beginning of feeding was 0.5-1.9 (H) and 1.1-2.4 min (R). Feeding times of each instar in both cohorts were over 10 min. Most specimens fed on hens defecated immediately after feeding, whereas those that fed on rabbits defecated within 1-5 min post-feeding. Similar numbers of males and females (50%) were obtained in both cohorts. An average of 2.1-2.3 eggs per female per day was noted in both cohorts, with eclosion rates of 95.4 (H) and 88.8% (R). Thus, it can be concluded that M. phyllosomus pallidipennis may take advantage of feeding in hens, as in rabbits, which could imply a higher risk of Trypanosoma cruzi transmission to humans and animals in its distribution area.

Impact of climate change on vector transmission of Trypanosoma cruzi (Chagas, 1909) in North America

Climate change can influence the geographical range of the ecological niche of pathogens by altering biotic interactions with vectors and reservoirs. The distributions of 20 epidemiologically important triatomine species in North America were modelled, comparing the genetic algorithm for rule-set prediction (GARP) and maximum entropy (MaxEnt), with or without topographical variables. Potential shifts in transmission niche for Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae) (Chagas, 1909) were analysed for 2050 and 2070 in Representative Concentration Pathway (RCP) 4.5 and RCP 8.5. There were no significant quantitative range differences between the GARP and MaxEnt models, but GARP models best represented known distributions for most species [partial-receiver operating characteristic (ROC) > 1]; elevation was an important variable contributing to the ecological niche model (ENM). There was little difference between niche breadth projections for RCP 4.5 and RCP 8.5; the majority of species shifted significantly in both periods. Those species with the greatest current distribution range are expected to have the greatest shifts. Positional changes in the centroid, although reduced for most species, were associated with latitude. A significant increase or decrease in mean niche elevation is expected principally for Neotropical 1 species. The impact of climate change will be specific to each species, its biogeographical region and its latitude. North American triatomines with the greatest current distribution ranges (Nearctic 2 and Nearctic/Neotropical) will have the greatest future distribution shifts. Significant shifts (increases or decreases) in mean elevation over time are projected principally for the Neotropical species with the broadest current distributions. Changes in the vector exposure threat to the human population were significant for both future periods, with a 1.48% increase for urban populations and a 1.76% increase for rural populations in 2050.

Habitat-Specific Occupancy and a Metapopulation Model of Triatoma sordida (Hemiptera: Reduviidae), a Secondary Vector of Chagas Disease, in Northeastern Argentina

Triatoma sordida Stål (Hemiptera: Reduviidae), a secondary vector of Trypanosoma cruzi Chagas (Kinetoplastida: Trypanosomatidae), occasionally colonizes human sleeping quarters in Paraguay, Bolivia, and Brazil, whereas only sylvatic and peridomestic populations are found in Argentina. We carried out a cross-sectional survey of house infestation in a well-defined rural area of northeastern Argentina to identify the key habitats of T. sordida; describe its spatial distribution in an apparently undisturbed setting under no recent insecticide treatment and use metapopulation theory to investigate these spatially structured populations. Timed-manual searches in 2,177 georeferenced sites from 368 houses yielded T. sordida in 78 sites (house infestation prevalence, 19.9%). Most triatomines occurred in chicken nests, chicken coops, and trees where chickens roosted (prime habitats). Goat or sheep corrals and pig corrals had a lower fraction of occupied sites (occupancies) and abundance. Both occupancy and catch increased with increasing refuge availability according to multimodel inference with model averaging. The majority of suitable habitats were unoccupied despite their proximity to occupied sites. The site-specific occurrence of T. sordida and Triatoma infestans Klug (Hemiptera: Reduviidae) was positively and homogeneously associated over ecotopes, showing no evidence of interspecific interference. An incidence function metapopulation model (including intersite distances and vector carrying capacity) predicted a fivefold greater occupancy relative to the observed pattern, suggesting the latter represented a transient state. T. sordida failed to colonize human sleeping quarters, thrived in peridomestic habitats occupied by chickens, and had a limited occupancy likely related to a poor colonizing ability and the relative instability of its prime habitats.

Comparative genomics analysis of triatomines reveals common first line and inducible immunity-related genes and the absence of Imd canonical components among hemimetabolous arthropods

Background

Insects operate complex humoral and cellular immune strategies to fend against invading microorganisms. The majority of these have been characterized in Drosophila and other dipterans. Information on hemipterans, including Triatominae vectors of Chagas disease remains incomplete and fractionated.

Results

We identified putative immune-related homologs of three Triatominae vectors of Chagas disease, Triatoma pallidipennis, T. dimidiata and T. infestans (TTTs), using comparative transcriptomics based on established immune response gene references, in conjunction with the predicted proteomes of Rhodnius prolixus, Cimex lecticularis and Acyrthosiphon pisum hemimetabolous. We present a compressive description of the humoral and cellular innate immune components of these TTTs and extend the immune information of other related hemipterans. Key homologs of the constitutive and induced immunity genes were identified in all the studied hemipterans.

Conclusions

Our results in the TTTs extend previous observations in other hemipterans lacking several components of the Imd signaling pathway. Comparison with other hexapods, using published data, revealed that the absence of various Imd canonical components is common in several hemimetabolous species.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2561-2) contains supplementary material, which is available to authorized users.

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.

Trypanosoma cruzi reservoir-triatomine vector co-occurrence networks reveal meta-community effects by synanthropic mammals on geographic dispersal

Contemporary patterns of land use and global climate change are modifying regional pools of parasite host species. The impact of host community changes on human disease risk, however, is difficult to assess due to a lack of information about zoonotic parasite host assemblages. We have used a recently developed method to infer parasite-host interactions for Chagas Disease (CD) from vector-host co-occurrence networks. Vector-host networks were constructed to analyze topological characteristics of the network and ecological traits of species’ nodes, which could provide information regarding parasite regional dispersal in Mexico. Twenty-eight triatomine species (vectors) and 396 mammal species (potential hosts) were included using a data-mining approach to develop models to infer most-likely interactions. The final network contained 1,576 links which were analyzed to calculate centrality, connectivity, and modularity. The model predicted links of independently registered Trypanosoma cruzi hosts, which correlated with the degree of parasite-vector co-occurrence. Wiring patterns differed according to node location, while edge density was greater in Neotropical as compared to Nearctic regions. Vectors with greatest public health importance (i.e., Triatoma dimidiata, T. barberi, T. pallidipennis, T. longipennis, etc), did not have stronger links with particular host species, although they had a greater frequency of significant links. In contrast, hosts classified as important based on network properties were synanthropic mammals. The latter were the most common parasite hosts and are likely bridge species between these communities, thereby integrating meta-community scenarios beneficial for long-range parasite dispersal. This was particularly true for rodents, >50% of species are synanthropic and more than 20% have been identified as T. cruzi hosts. In addition to predicting potential host species using the co-occurrence networks, they reveal regions with greater expected parasite mobility. The Neotropical region, which includes the Mexican south and southeast, and the Transvolcanic belt, had greatest potential active T. cruzi dispersal, as well as greatest edge density. This information could be directly applied for stratification of transmission risk and to design and analyze human-infected vector contact intervention efficacy.

A global systematic review of Chagas disease prevalence among migrants

Human migration has been identified as a potential factor for increased Chagas disease risk and has transformed the disease from a Latin American problem to a global one. We conducted a systematic review of the scientific literature between 2004-2014 in order to: summarize recent seroprevalence estimates of Chagas disease among Latin American migrants, in both endemic and non-endemic settings; compare seroprevalence estimates in migrants to countrywide prevalence estimates; and identify risk factors for Chagas disease among migrants. A total of 320 studies were screened and 23 studies were included. We found evidence that the prevalence of Chagas disease is higher than expected in some migrant groups and that reliance on blood donor screening prevalence estimates underestimates the burden of disease. Overall there is a dearth of high quality epidemiologic studies on the prevalence of Chagas disease in migrants, especially among intra-regional migrants within Latin America. Given that this zoonotic disease cannot likely be eradicated, improved surveillance and reporting is vital to continuing control efforts. More accurate health surveillance of both Latin American migrants and the Chagas disease burden will help countries appropriately scale up their response to this chronic disease. Overall, improved estimates of Chagas disease among migrants would likely serve to highlight the real need for better screening, diagnostics, and treatment of individuals living with the disease.

Social Representations and Practices Towards Triatomines and Chagas Disease in Calakmul, México

Vector-borne transmission of Trypanosoma cruzi (VBTTc) is dependent on the concomitant interaction between biological and environmental hazard over the entire landscape, and human vulnerability. Representations and practices of health-disease-care-seeking and territorial appropriation and use were analyzed for VBTTc in a qualitative ethnographic study in the Zoh-Laguna landscape, Campeche, Mexico. In-depth interviews and participatory observation explored representations and practices regarding ethno-ecological knowledge related to vector-transmission, health-disease-care-seeking, and land use processes. The population has a broad knowledge of biting insects, which they believe are all most abundant in the rainy season; the community´s proximity to natural areas is perceived as a barrier to control their abundance. Triatomines are mostly recognized by men, who have detailed knowledge regarding their occurrence and association with mammals in non-domestic fragments, where they report being bitten. Women emphasize the dermal consequences of triatomine bites, but have little knowledge about the disease. Triatomine bites and the chinchoma are "normalized" events which are treated using home remedies, if at all. The neglected condition of Chagas disease in Mexican public health policies, livelihoods which are dependent on primary production, and gender-related knowledge (or lack thereof) are structural circumstances which influence the environment and inhabitants´ living conditions; in turn, these trigger triatomine-human contact. The most important landscape practices producing vulnerability are the activities and mobility within and between landscape fragments causing greater exposure of inhabitants primarily in the dry season. A landscape approach to understanding vulnerability components of VBTTc from health-disease-care-seeking perspectives and based on territorial appropriation and use, is essential where there is continuous movement of vectors between and within all habitats. An understanding of the structural factors which motivate the population´s perceptions, beliefs, and practices and which create and maintain vulnerability is essential to develop culturally relevant and sustainable community-based VBTTc prevention and control.

Positive deviance study to inform a Chagas disease control program in southern Ecuador

Chagas disease is caused by Trypanosoma cruzi, which is mainly transmitted by the faeces of triatomine insects that find favourable environments in poorly constructed houses. Previous studies have documented persistent triatomine infestation in houses in the province of Loja in southern Ecuador despite repeated insecticide and educational interventions. We aim to develop a sustainable strategy for the interruption of Chagas disease transmission by promoting living environments that are designed to prevent colonisation of rural houses by triatomines. This study used positive deviance to inform the design of an anti-triatomine prototype house by identifying knowledge, attitudes and practices used by families that have remained triatomine-free (2010-2012). Positive deviants reported practices that included maintenance of structural elements of the house, fumigation of dwellings and animal shelters, sweeping with "insect repellent" plants and relocation of domestic animals away from the house, among others. Participants favoured construction materials that do not drastically differ from those currently used (adobe walls and tile roofs). They also expressed their belief in a clear connection between a clean house and health. The family's economic dynamics affect space use and must be considered in the prototype's design. Overall, the results indicate a positive climate for the introduction of housing improvements as a protective measure against Chagas disease in this region.

Ecological and sociodemographic determinants of house infestation by Triatoma infestans in indigenous communities of the Argentine Chaco

BACKGROUND

The Gran Chaco ecoregion, a hotspot for Chagas and other neglected tropical diseases, is home to >20 indigenous peoples. Our objective was to identify the main ecological and sociodemographic determinants of house infestation and abundance of Triatoma infestans in traditional Qom populations including a Creole minority in Pampa del Indio, northeastern Argentina.

METHODS

A cross-sectional survey determined house infestation by timed-manual searches with a dislodging aerosol in 386 inhabited houses and administered questionnaires on selected variables before full-coverage insecticide spraying and annual vector surveillance. We fitted generalized linear models to two global models of domestic infestation and bug abundance, and estimated coefficients via multimodel inference with model averaging.

PRINCIPAL FINDINGS

Most Qom households were larger and lived in small-sized, recently-built, precarious houses with fewer peridomestic structures, and fewer livestock and poultry than Creoles'. Qom households had lower educational level and unexpectedly high residential mobility. House infestation (31.9%) was much lower than expected from lack of recent insecticide spraying campaigns and was spatially aggregated. Nearly half of the infested houses examined had infected vectors. Qom households had higher prevalence of domestic infestation (29.2%) than Creoles' (10.0%), although there is large uncertainty around the adjusted OR. Factors with high relative importance for domestic infestation and/or bug abundance were refuge availability, distance to the nearest infested house, domestic insecticide use, indoor presence of poultry, residential overcrowding, and household educational level.

CONCLUSIONS AND SIGNIFICANCE

Our study highlights the importance of sociodemographic determinants of domestic infestation such as overcrowding, education and proximity to the nearest infested house, and corroborates the role of refuge availability, domestic use of insecticides and household size. These factors may be used for designing improved interventions for sustainable disease control and risk stratification. Housing instability, household mobility and migration patterns are key to understanding the process of house (re)infestation in the Gran Chaco.

Eco-epidemiology of Chagas disease in an endemic area of Colombia: risk factor estimation, Trypanosoma cruzi characterization and identification of blood-meal sources in bugs

The Sierra Nevada de Santa Marta (SNSM) is a mountainous area in Colombia that is highly endemic to Chagas disease. We explored some eco-epidemiological attributes involved in the Chagas disease transmission scenario in three Indigenous communities. An epidemiological survey was done, where parasite infection in reservoirs and insects, Trypanosoma cruzi genotyping, identification of blood-meal sources in intradomiciliary insects using the high-resolution melting technique, and some risk factors were evaluated. The results suggest that several dwelling conditions such as thatched palm roofs and mud walls carried the highest risk of finding intradomiciliary Rhodnius prolixus, which 56.41% were infected with T. cruzi and fed with human blood. Moreover, T. cruzi Ia was the most frequent haplotype found in insects. These results indicate the existence of a domestic T. cruzi transmission cycle that does not overlap with the sylvatic cycle, and highlight the need for efficient entomological control focused to this area.

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.

The major vectors of Chagas disease are species of triatomine bugs adapted to human sleeping quarters and peridomestic annexes where they feed on humans and domestic or synanthropic mammals or birds. Knowledge of the demography and nutritional status of Triatominae in real-life settings is still fragmentary, and this affects our ability to prevent or reduce house reinfestation after insecticide spraying. In addition to showing where the bugs are likely to live (occupancy and density information), our observations and analysis of flight dispersal provide insights into where bugs are likely to originate. Data on nymphal and adult sex ratios, nutritional status, and female fecundity point to the key ecotopes and sites driving the population growth of the bugs and fueling house reinfestation. Focusing control efforts on the three ecotopes (human sleeping quarters, storerooms, and goat corrals) that housed reactive, human-fed bugs 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 in a typical house compound and community is required to prevent feeding on humans, bug population growth, and bug dispersal simultaneously.

Factors associated with peridomestic Triatoma sanguisuga (Hemiptera: Reduviidae) presence in southeastern Louisiana

Although rare, there have been isolated reports of autochthonous transmission of Trypanosoma cruzi Chagas in the United States. In June 2006, a human case of domestically transmitted T. cruzi was identified in southern Louisiana. To examine the localized risk of human T. cruzi infection in the area surrounding the initial human case, environmental surveys of households in the area and a serological survey of the residents were performed between September 2008 and November 2009. Human T. cruzi infection was determined using a rapid antigen field test, followed by confirmatory enzyme-linked immunosorbent assay testing in the laboratory. A perimeter search of each participating residence for Triatoma sanguisuga (LeConte), the predominant local triatomine species, was also performed. No participating individuals were positive for antibodies against T. cruzi; however, high levels of T. cruzi infection (62.4%) were detected in collected T. sanguisuga. Households with T. sanguisuga presence were less likely to use air conditioning, and more likely to have either chickens or cats on the property. While the human risk for T cruzi infection in southeastern Louisiana is low, a high prevalence of infected T. sanguisuga does indicate a substantial latent risk for T. cruzi peridomestic transmission. Further examination of the behavior and ecology of T. sanguisuga in the region will assist in refining local T. cruzi risk associations.

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

In Guatemala prior to control initiatives, the main vectors of Trypanosoma cruzi, the causative agent of Chagas disease, were Rhodnius prolixus and Triatoma dimidiata. This study conducted in 2006 in the department of Chiquimula recorded a high level of T. dimidiata infestation and an absence of R. prolixus in all surveyed communities. In Guatemala, the presence of T. dimidiata as domestic, peridomestic and sylvatic populations results in control difficulties as houses are re-infested from the surrounding environment. Entomological surveys, the current method used to select houses in need of control efforts, are labour intensive and time consuming. A time- and cost-effective way to prioritize houses for evaluation and subsequent treatment is the stratification of houses based on the risk of triatomine infestation. In the present study, 17 anthropogenic risk factors were evaluated for associations with house infestation of T. dimidiata including: wall, floor and roof type. There was an increased likelihood of domestic infestation with T. dimidiata associated with the presence of dirt floors (18/29; OR 8.075, 95% CI 2.13-30.6), uncoated bajareque walls (12/17; OR 4.80, 95% CI 1.35-17.1) and triatomine-like faeces on walls (16/26; OR 3.89, 95% CI 1.19-12.7). These factors could be used to target control of T. dimidiata to communities with an increased risk of being infested.

Eco-bio-social determinants for house infestation by non-domiciliated Triatoma dimidiata in the Yucatan Peninsula, Mexico

BACKGROUND

Chagas disease is a vector-borne disease of major importance in the Americas. Disease prevention is mostly limited to vector control. Integrated interventions targeting ecological, biological and social determinants of vector-borne diseases are increasingly used for improved control.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated key factors associated with transient house infestation by T. dimidiata in rural villages in Yucatan, Mexico, using a mixed modeling approach based on initial null-hypothesis testing followed by multimodel inference and averaging on data from 308 houses from three villages. We found that the presence of dogs, chickens and potential refuges, such as rock piles, in the peridomicile as well as the proximity of houses to vegetation at the periphery of the village and to public light sources are major risk factors for infestation. These factors explain most of the intra-village variations in infestation.

CONCLUSIONS/SIGNIFICANCE

These results underline a process of infestation distinct from that of domiciliated triatomines and may be used for risk stratification of houses for both vector surveillance and control. Combined integrated vector interventions, informed by an Ecohealth perspective, should aim at targeting several of these factors to effectively reduce infestation and provide sustainable vector control.

Ecological connectivity of Trypanosoma cruzi reservoirs and Triatoma pallidipennis hosts in an anthropogenic landscape with endemic Chagas disease

Traditional methods for Chagas disease prevention are targeted at domestic vector reduction, as well as control of transfusion and maternal-fetal transmission. Population connectivity of Trypanosoma cruzi-infected vectors and hosts, among sylvatic, ecotone and domestic habitats could jeopardize targeted efforts to reduce human exposure. This connectivity was evaluated in a Mexican community with reports of high vector infestation, human infection, and Chagas disease, surrounded by agricultural and natural areas. We surveyed bats, rodents, and triatomines in dry and rainy seasons in three adjacent habitats (domestic, ecotone, sylvatic), and measured T. cruzi prevalence, and host feeding sources of triatomines. Of 12 bat and 7 rodent species, no bat tested positive for T. cruzi, but all rodent species tested positive in at least one season or habitat. Highest T. cruzi infection prevalence was found in the rodents, Baiomys musculus and Neotoma mexicana. In general, parasite prevalence was not related to habitat or season, although the sylvatic habitat had higher infection prevalence than by chance, during the dry season. Wild and domestic mammals were identified as bloodmeals of T. pallidipennis, with 9% of individuals having mixed human (4.8% single human) and other mammal species in bloodmeals, especially in the dry season; these vectors tested >50% positive for T. cruzi. Overall, ecological connectivity is broad across this matrix, based on high rodent community similarity, vector and T. cruzi presence. Cost-effective T. cruzi, vector control strategies and Chagas disease transmission prevention will need to consider continuous potential for parasite movement over the entire landscape. This study provides clear evidence that these strategies will need to include reservoir/host species in at least ecotones, in addition to domestic habitats.

The development and validation of a risk score for household infestation by Triatoma infestans, a Bolivian vector of Chagas disease

Chagas disease, primarily spread in Bolivia by the vector Triatoma Infestans, persists as an important public health problem. Preventative insecticide campaigns target spraying on the basis of anecdotal evidence and there is a need for an accurate classification score to correctly identify 'at risk' houses. Data were collected from 337 households on 11 variables through the use of a standardised questionnaire and survey. Risk factors for infestation were identified and a risk score was developed and validated on a separate cohort of 165 houses. Five significant risk factors were identified: cracks in the walls of houses; adobe walls; junk in the peridomiciliary area; no insecticide spraying in the previous two years; and freely ranging animals. A risk score was generated and then calculated for each house. Three risk categories were defined: low, medium and high risk. In the development cohort the infestation rates were 2%, 18% and 69% respectively. The corresponding infestation rates in the validation cohort were 7%, 30% and 75% respectively. Sensitivity and specificity for this test were 81% and 84% and the positive predictive and negative predictive values were 71% and 90%. The risk score developed could be used to inform decision making in underfunded multilateral preventative initiatives.

Epidemiology of American trypanosomiasis (Chagas disease)

Trypanosoma cruzi, the cause of American trypanosomiasis, or Chagas disease, is a protozoan parasite that is enzootic and endemic in much of the Americas, where it infects a wide variety of wild and domestic mammals as well as many species of triatomine vectors, in addition to humans. Historically, vector-borne transmission of T. cruzi has been the most important mechanism through which humans have become infected with the parasite, but transmission by blood transfusion and congenital transmission also have been important. In many of the endemic countries transmission of T. cruzi has improved markedly in recent years as vector control and donor screening programs have been implemented on a widespread basis. In the United States autochthonous transmission of T. cruzi appears to be extremely rare. Five persons are known to have become infected with T. cruzi through organ transplants here, and prior to the implementation of blood donor screening in 2007 five instances of transmission by transfusion had been reported. Current estimates put the total number of T. cruzi-infected persons living in the United States at 300,000, essentially all of whom are immigrants from the endemic countries. The obstacles that stand in the way of the total elimination of T. cruzi transmission throughout the endemic range are economic and political, and no major technological advances are needed to accomplish this goal.

Risk factors for intradomiciliary infestation by the Chagas disease vector Triatoma dimidiatain Jutiapa, Guatemala

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.

Urban infestation by Triatoma dimidiata in the city of Mérida, Yucatán, México

The observation of widespread seasonal infestation by Triatoma dimidiata in rural villages around the city of Mérida, Yucatán, México, led us to reconsider the presence of Chagas disease vectors and the risk factors for house infestation in the city itself. Bugs were collected in 150 houses from 30 neighborhoods distributed throughout the city. We observed a widespread infestation by T. dimidiata in the city, with 38% of infested houses and 48% of the collected triatomines testing positive for Trypanosoma cruzi. House infestation by triatomines was greatest during the months of April-June. Infestation risk factors were related with backyard characteristics rather than housing type and quality of housing: houses located in the periphery of the city, with abandoned lots on the sides and large backyards, had a higher risk of being infested, while those with mosquito screens and occasional insecticide spraying in their yards had a lower risk. Several human blood meals were also identified and seropositive patients were distributed through most of the city, confirming the potential for urban transmission of Chagas disease to humans. This study shows that urban Chagas disease should not be neglected and surveillance programs should be implemented to further evaluate the magnitude of the problem.

House-level risk factors for triatomine infestation in Colombia

BACKGROUND

Chagas disease, transmitted domestically by triatomine bugs, is the most important vector-borne disease in Latin America. The association between triatomine infestation and housing characteristics was investigated based on a standardized survey in 41 971 houses in 15 Departments in Colombia.

METHODS

Multivariate logistic regression was used to test for associations of two highly correlated infestation measures of infestation (householders reporting having seen triatomines inside the house, and sending triatomines to the survey team), with 15 household-level risk factors. Risks were measured relative to a reference category of houses with up to three inhabitants, area up to 50 m(2), unplastered adobe walls, thatch roof and no outbuildings or domestic animals.

RESULTS

The probability of seeing triatomines was highest for households with over seven inhabitants (OR = 1.24, 95% CI 1.11-1.39), overhead storage space (OR = 1.16, 95% CI 1.03-1.32), grain shed (OR = 1.25, 95% CI 1.02-1.52), cats (OR = 1.27, 95% CI 1.14-1.42) and pigs (OR = 1.16, 95% CI 1.03-1.30). Lowest risks were in houses with wooden walls (OR = 0.46, 95% CI 0.34-0.61), fully plastered walls (OR = 0.78, 95% CI 0.68-0.88), roofs made of tiles (OR = 0.51, 95% CI 0.33-0.78) and flagstone floors (OR = 0.57, 95% CI 0.42-0.76). Results for householders returning triatomines support this set of risk factors, but with wider confidence intervals.

CONCLUSIONS

Surveillance of a few easily assessed household characteristics provides an accurate, rapid assessment of house-level variation in risk. Measured effect sizes for specific structural characteristics could be used to maximize the cost-effectiveness of programmes to reduce vector infestation and interrupt Chagas disease transmission by improving house quality.

Biology of three species of the Meccus phyllosomus complex (Hemiptera: Reduviidae: Triatominae) fed on blood of hens and rabbits

Aspects related to hatching, life time, number of blood meals to molt, mortality, feeding time and postfeed defecation delay for each instar of Meccus phyllosomus, M. mazzottii, and M. bassolsae, life-cycle were evaluated and compared in two cohorts of each of those three species, fed on hens or rabbits. No significant (p > 0.05) differences were recorded among cohorts fed on hens respect to cohorts fed on rabbits in M. phyllosomus and M. mazzottii and the average time of hatching was 21.5 days for cohorts fed on hens and 22.5 for cohorts fed on rabbits. Average egg-to-adult development times were no significant (p > 0.05) different between both cohorts of M. phyllosomus and M. mazzotti, independent of the blood meal source. The average span in days for each instar fed on hens was not significantly different to the average span for each instar fed on rabbits, when comparisons were made by species. The number of blood meals at each nymphal instar varied from 1 to 6 in both cohorts of each species. The mortality rates were higher on older nymphs, in both cohorts of M. phyllosomus and M. bassolsae, whereas they were higher on first instar nymphs on M. mazzottii. Mean feeding time was no significant (p > 0.05) different in triatomines fed on hens or fed on rabbits, when each species were compared separately. A similar number of nymphs of each cohort, completed the cycle. Defecation delay was no significant (p > 0.05) different when cohorts fed on hens and fed on rabbits were compared by species. Most of the studied parameters showed no significant (p > 0.05) differences among those cohorts fed on hens and for fed on rabbits, which could mean a high degree of association of those species with birds as much as mammals, under wild conditions, increasing their capacity to colonize human dwellings.

Peridomestic colonization of Triatoma longipennis (Hemiptera, Reduviidae) and Triatoma barberi (Hemiptera, Reduviidae) in a rural community with active transmission of Trypanosoma cruzi in jalisco state, Mexico

Infestation of peridomiciles is likely a major risk factor for Chagas disease transmission in Jalisco state, Mexico. An entomological and serological survey of a typical village was conducted between July and September 2003. The peridomestic areas of 100 dwellings were visited and triatomines were searched manually in 369 potential sites. A total of 1821 Triatoma longipennis (93.2%) or Triatoma barberi was captured. Both species frequently occurred in sympatry. The infestation index was 60% for T. longipennis and 16% for T. barberi. T. longipennis occurred throughout the village. Colonization indices were high for T. longipennis (93%) and T. barberi (75%), suggesting that both species have adapted to peridomestic habitats. The bug population size was larger for T. longipennis than for T. barberi. Five very large colonies of T. longipennis were recorded whereas only 1 or 2 bugs were observed in 38% of the positive sites, which suggests intense dispersal activity. Both species exhibited high infection prevalence with Trypanosoma cruzi (46%). Only T. cruzi lineage I was detected. Human seroprevalence was 1.8%. This study serves as an entomological overview of peridomiciliar triatomine colonization in a Mexican village and highlights the current risk of Chagas disease transmission.

Evaluation of cultures of Saccharomyces cerevisae as baits for Triatoma dimidiata and Triatoma pallidipennis

We tested the attraction of Triatoma dimidiata and T. pallidipennis to traps baited with yeast volatiles. Two traps were simultaneously presented in opposite sides of an experimental arena. One trap presented a yeast culture in sucrose solution, while the other contained sucrose solution as control. A first experimental series was done without offering a central refuge for bugs. In a second series, one shelter where the insects could hide was offered and the traps were presented afterwards. In the first series, yeast baited traps attracted significantly more insects than control ones for both species. In the second series, T. pallidipennis was significantly attracted to yeast, whereas T. dimidiata was not attracted. The potential use of yeast baited traps for capturing these vectors of Chagas disease is discussed.

HOUSEHOLD RISK FACTORS FOR TRYPANOSOMA CRUZI SEROPOSITIVITY IN TWO GEOGRAPHIC REGIONS OF ECUADOR

Few studies on the relationship between environmental factors and Trypanosoma cruzi transmission have been conducted in Ecuador. We conducted a cross-sectional study of household risk factors for T. cruzi seropositivity in 2 distinct geographical regions of Ecuador. Exposure information was collected via household surveys, and subjects were tested for serological evidence of T. cruzi infection. In total, 3,286 subjects from 997 households were included. In the coastal region, factors associated with seropositivity were living in a house with a palm roof (odds ratio [OR] = 2.63, 95% confidence interval, [1.61. 4.27]), wood walls (OR = 5.75 [2.04, 16.18]), or cane walls (OR = 2.81 11.31, 6.04]), and the presence of firewood in the peridomicile (OR = 2.48 [1.54, 4.01]). Accumulation of trash outside the home was associated with a reduced risk of seropositivity (OR = 0.25 [0.12, 0.51]). In the Andean region, living in a house with adobe walls was the only factor predictive of T. cruzi seropositivity. In conclusion, risk factors for T. cruzi transmission in Ecuador varied by geographic region, probably because of differing behavior of the triatomine vector species in each region. An understanding of the transmission dynamics of T. cruzi in a particular area is necessary for the development of effective Chagas disease control strategies in those areas.

Infestation by Triatoma pallidipennis (Hemiptera: Reduviidae: Triatominae) is associated with housing characteristics in rural Mexico

Long-term control of Chagas disease requires not only interruption of the human transmission cycle of Trypanosoma cruzi Schyzotrypanum, Chagas, 1909 by controlling its domestic triatomine vectors but also surveillance to prevent reinfestation of residences from sylvatic or persistent peridomestic populations. Although a number of potential risk factors for infestation have been implicated in previous studies, the explanatory power of resulting models has been low. Two years after cessation of triatomine vector control efforts in the town of Chalcatzingo, Morelos, 78 environmental, socioecological, and spatial variables were analyzed for association with infestation by Triatoma pallidipennis Stal 1872 (Hemiptera: Reduviidae: Triatominae), the principal vector of T. cruzi. We studied 712 residences in this rural community to identify specific intradomestic and peridomestic risk factors that predicted infestation with T. pallidipennis. From numerous characteristics that were identified as correlated with infestation, we derived multivariate logistic regression models to predict residences that were more or less likely to be infested with T. pallidipennis. The most important risk factors for infestation included measurements of house age, upkeep, and spatial location in the town. The effects of certain risk factors on infestation were found to be modified by spatial characteristics of residences. The results of this study provide new information regarding risk factors for infestation by T. pallidipennis that may aid in designing sustainable disease control programs in rural Mexico.

Could the Chagas disease elimination programme in Venezuela be compromised by reinvasion of houses by sylvatic Rhodnius prolixus bug populations?

The Andean Pact Initiative (1997) committed Andean countries to eliminate vectorial transmission of Chagas disease by 2010 via widespread residual insecticide spraying. In Venezuela, this aim could be compromised by reinvasion of houses by palm tree populations of the major vector Rhodnius prolixus. To test this hypothesis, a multivariate logistic regression was undertaken of risk factors for triatomine infestation and colonization in 552 houses and 1068 peri-domestic outbuildings in Barinas State. After adjusting for other risk factors, including palm roofs, R. prolixus infestation and colonization of outbuildings (and, to some extent, houses) was significantly associated with proximity to high densities of Attalea butyracea palm trees. House infestation and/or colonization was also positively associated with bug density in peri-domestic outbuildings, the presence of pigsties and nests. Hence, R. prolixus populations in ineffectively sprayed outbuildings could also provide an important source of house re-infestations. The secondary vector Triatoma maculata was mainly found associated with the presence of hens nesting both indoors and outdoors.

Epidemiological risk for Trypanosoma cruzi transmission by species of Phyllosoma complex in the occidental part of Mexico

Domestic and peridomestic triatomine populations were collected in three rural Mexican communities of Jalisco, Nayarit and Zacatecas states. Triatoma longipennis and T. picturata (Phyllosoma complex) were the principal species unequally distributed in the villages: T. longipennis was the main species in two communities and T. picturata in the third one. Peridomestic infestation and colonization indexes were remarkably high ranging from 26.1% to 50% and from 58.3% to 85.7%, respectively. Moreover, domestic (indoor) infestation was observed in only one of the communities infested by T. longipennis. The preliminary study of temporal variation indicates increasing trend of the triatomine population and infestation rates during the dry season. Triatomine infection rates ranged from 41.2% to 60.2% and all the flagellate isolates were assigned to T. cruzi I. The majority of the dwellings were built with modern building materials and the sanitary conditions were generally good. High peridomestic infestations must be considered as a risk factor of Chagas disease transmission and further studies are needed to better understand the peridomestic conditions favoring the establishment of the triatomines. The contribution of such study to enlarger knowledge of epidemiological features of Chagas disease in Mexico is considered.

Risk factors associated with house infestation by the Chagas disease vector Triatoma pallidipennis in Cuernavaca metropolitan area, Mexico

Chagas disease caused by infection with Trypanosoma cruzi Chagas (Kinetoplastida: Trypanosomatidae) is widespread in Mexico, transmitted by various triatomine bugs (Hemiptera: Reduviidae). The only domestic vector in Cuernavaca (population 650 000) is Triatoma pallidipennis (Ståhl) with T. cruzi seroprevalence ranging from 1% to 9% in the resident human population. We surveyed possible risk factors for T. pallidipennis infestation at Cuernavaca (altitude 1200-2200 m) on south-western slopes of the Sierra Madre Occidental. This metropolitan area (with five administrative counties) has rapid urbanization, forested environs and proliferation of 'weekend housing' for visitors from Mexico City, 60 km to the north. To assess factors associated with T. pallidipennis infestation, we first stratified Cuernavaca by altitude and by socio-economic status of population catchment units (PCUs). Within each PCU, one to three blocks were chosen for cluster sampling (three houses/block) and information about Chagas disease was distributed. After obtaining signed consent from householders, representative houses were routinely and opportunistically inspected for T. pallidipennis and surveyed for demographic, economic, physical and other potential risk factors. Of the 1129 houses assessed, T. pallidipennis was found in 4.1% (range 3.0-6.8% per county) and the T. cruzi infection rate was approximately 50% in bugs. Rates of house infestation in poor PCUs were double those in higher socio-economic strata (odds ratio 2.12, confidence interval 1.03-4.3), with >4-fold greater crowding index of T. pallidipennis. The bug density index was inversely correlated with PCU altitude and socio-economic category (altitude of homes being associated with prosperity), while the bug colonization index (presence of nymphs indicating breeding) did not vary significantly across the PCU categories, but did vary according to altitude. Multivariate regression analysis showed that the most significant risk factors associated with T. pallidipennis infestation were lower altitude (linked with lower socio-economic status), garden area >80 m(2), dogs at liberty to enter the house, occurrence of squirrels and opossums around the house, presence of pigs in the surrounding area and having at least one of the adjacent lots empty (unconstructed). Householders who had received information about Chagas disease comprised 33% from infested houses (14/42) but only 15% from non-infested houses (148/984). Hence, the awareness of Chagas disease was significantly associated with having a bug-free house (P < 0.01). When shown specimens of T. pallidipennis, the proportions of householders who recognized them were 78% from infested houses but only 29% of those with uninfested houses. Given the low infestation rates and the high capacity of the population to act appropriately once they have received information regarding this disease and its vector, relevant health education is expected to have a significant impact on triatomine control in this metropolitan area.