House infestation dynamics and feeding sources of Triatoma dimidiata in central Veracruz, Mexico

Chagas disease is endemic in the state of Veracruz, Mexico, and we investigated here the dynamics of house infestation by Chagas disease vectors to understand disease transmission and design effective control interventions. Bug collections in 42 rural villages confirmed the widespread distribution of Triatoma dimidiata in central Veracruz. Unexpectedly, collection data further indicated a clear pattern of seasonal infestation by mostly adult bugs. Analysis of feeding sources with a polymerase chain reaction-heteroduplex assay indicated a frequent feeding on humans, in agreement with the high seroprevalence previously observed. Feeding sources also confirmed a significant dispersal of bugs between habitats. High dispersal capabilities and seasonal infestation may thus be a shared characteristic of several of the T. dimidiata sibling species from this complex. It would thus be critical to adapt vector control interventions to this behavior to improve their efficacy and sustainability, as the control of T. dimidiata has been notoriously challenging.     

Patterns of house infestation dynamics by non-domiciliated Triatoma dimidiata reveal a spatial gradient of infestation in rural villages and potential insect manipulation by Trypanosoma cruzi

Objective  Chagas disease is a major vector-borne parasitic disease in Latin America, primarily transmitted to humans by triatomine vectors. Non-domiciliated triatomine species such as Triatoma dimidiata in the Yucatan peninsula, Mexico, can transiently invade houses and are emerging as a major challenge to control Trypanosoma cruzi transmission to humans. We analyzed the spatio-temporal spreading of house infestation by T. dimidiata in four rural villages.
Methods  Triatomines were collected in four rural villages over a 2 years period, and the spatio-temporal patterns of infestation were analyzed.
Results  Triatomines were consistently more abundant at the periphery of villages than in centers, indicating a much higher risk of T. cruzi transmission at the periphery. Male T. dimidiata were found further in the center of the village, while females remained closer to the periphery, suggesting differential dispersal capabilities between sexes, although the timing of dispersal appeared identical. Surprisingly, infected females were consistently collected in houses much further from the surrounding bushes than non-infected females, while the distribution of males was unaffected by their T. cruzi infection status, suggesting an increased dispersal capability in infected females.
Conclusion  The spatial structure of infestation should be taken into account for the prioritization of vector control activities within villages, and spatially targeted interventions may be explored. A potential vector manipulation by T. cruzi, observed for the first time in triatomines, may favor parasite transmission to new hosts.     

Impregnated netting slows infestation by Triatoma infestans

We used sentinel animal enclosures to measure the rate of infestation by the Chagas disease vector, Triatoma infestans, in an urban community of Arequipa, Peru, and to evaluate the effect of deltamethrin-impregnated netting on that rate. Impregnated netting decreased the rate of infestation of sentinel enclosures (rate ratio, 0.23; 95% confidence interval, 0.13-0.38; P < 0.001), controlling for the density of surrounding vector populations and the distance of these to the sentinel enclosures. Most migrant insects were early-stage nymphs, which are less likely to carry the parasitic agent of Chagas disease, Trypanosoma cruzi. Spread of the vector in the city therefore likely precedes spread of the parasite. Netting was particularly effective against adult insects and late-stage nymphs; taking into account population structure, netting decreased the reproductive value of migrant populations from 443.6 to 40.5. Impregnated netting can slow the spread of T. infestans and is a potentially valuable tool in the control of Chagas disease.     

Geographic distribution of Triatoma dimidiata and transmission dynamics of Trypanosoma cruzi in the Yucatan peninsula of Mexico

Chagas disease represents a major public health concern in most of Latin America, and its control is currently based on vector control and blood bank screening. We investigated the geographic distribution and seasonal variations in triatomine populations in the Yucatan peninsula of Mexico to obtain entomologic data for the optimization of potential control programs. We collected domiciliated and peri-domiciliated Triatoma dimidiata from 115 houses in 23 villages distributed throughout most of the peninsula. A high abundance of bugs was observed in the northern part of the peninsula, indicating a prioritary area for vector control. Part of this distribution could be attributed to the type of vegetation. We also documented strong seasonal variations in T. dimidiata populations, with a higher abundance during the hot and dry season in April-June. These variations, associated with reduced year-round colonization of houses and the analysis of developmental stage structure, suggest that flying adults seasonally invading houses may play a larger role than domiciliated bugs in transmission of Trypanosoma cruzi to humans. The importance of this transmission dynamics may not be limited to the Yucatan peninsula, but may be a general mechanism contributing to natural transmission that should be taken into account in other regions for the design and optimization of control strategies.     

House-Level Risk Factors for Triatoma dimidiata Infestation in Colombia

In Colombia, the main vectors of Trypanosoma cruzi, the causative agent of Chagas disease, are Rhodnius prolixus and Triatoma dimidiata. T. dimidiata is present in the east region of Colombia as domestic, peridomestic, and sylvatic populations, resulting in difficulties for its control. A cost-effective way to prioritize houses for treatment is to stratify houses based on risk factors. In this study, risk factors were evaluated for potential associations with domicile infestation of T. dimidiata. There was an increased likelihood of domestic infestation associated with the presence of mixed roofs (odds ratio [OR] = 36.14, 95% confidence interval [95% CI] = 12.21–106.97), cats (OR = 3.94, 95% CI = 1.36–11.38), rock piles (OR = 5.28, 95% CI = 1.64–16.98), and bushes with height above 10 m (OR = 11.21, 95% CI = 2.08–60.45). These factors could be used to target surveillance and control of T. dimidiata to houses with an increased risk of being infested.     

Two Triatoma dimidiata clades (Chagas disease vector) associated with different habitats in southern Mexico and Central America

Triatoma dimidiata is the only reported Chagas disease vector in Campeche, Mexico. The purpose of this study was to determine the genetic variability of vectors from Campeche coastal and rain forest areas and establish a phylogenetic relationship with other T. dimidiata populations by analyzing the internal transcribed spacer-2 (ITS-2) region. The sequence length of samples from Campeche ranged from 469 to 478 basepairs. The ITS-2 variability among the populations enabled us to classify them into two clades with an 18-22 nucleotide difference. The genetic distance (0.042) between them confirms this divergence. Phylogenetic analysis of gene genealogies confirmed these two clades. Furthermore, the population genetic analyses showed two groups with little genetic similarity or migration between them. One group was associated with the tropical forest area and the other group was associated with a mainly coastal distribution. This correlation was also observed when T. dimidiata from other regions of Mexico and Central America were analyzed.     

Feeding preferences of Triatoma dimidiata maculipennis in Yucatan, Mexico.

To determine whether a low preference for human blood by Triatoma dimidiata maculipennis Stal, 1859, the only known vector of Chagas' disease in Yucatan, Mexico, would account for the low prevalence of antibodies to Trypanosoma cruzi in man in the area, the intestinal contents of 924 bugs were tested against antisera to blood antigens of chicken, opossum, dog, bat, monkey, pig, goat, rabbit, horse, human, rat, ox, cat, and armadillo. Although the chicken was the primary host, man was fed upon frequently; thus, the hypothesis was rejected. Other explanations must be found for the relative lack of antibodies against T. cruzi in humans in Yucatan.     

Assessment of Triatoma dimidiata dispersal in the Yucatan Peninsula of Mexico by morphometry and microsatellite markers

In the Yucatán Peninsula of Mexico, the main vector of Chagas disease is Triatoma dimidiata. Field studies suggest that natural transmission occurs through transient and seasonal invasion of houses by sylvatic/peridomestic triatomines, rather than through persistent domiciliated bug populations. We investigated the genetic structure of T. dimidiata populations, using morphometry and microsatellite markers, to assess dispersal of individuals in this triatomine species and to understand the dynamics of domestic infestation. We observed low phenotypic and genetic differentiation among populations from different villages, with an FST of only 0.0553, which suggested a weak but significant population structure at this level. Similarly low but significant differences were observed among populations from the same village but different biotopes (sylvatic, peridomestic, and domestic), with FST values ranging from 0.0096 to 0.0455. These data suggested elevated dispersal of bugs between biotopes (Nm = 5-25), which was confirmed by likelihood and Bayesian assignment tests. A proportion of bugs collected within domiciles were significantly assigned to peridomestic and sylvatic areas. This study showed that T. dimidiata has important dispersal capabilities that can explain the seasonal pattern of domicile infestation by peridomestic and sylvatic bugs. Therefore, dispersal should be taken into account in the design of effective vector control strategies.     

Environmental Determinants of the Distribution of Chagas Disease Vector Triatoma dimidiata in Colombia

Triatomadimidiata (Hemiptera: Reduviidae) is a secondary vector of Trypanosoma cruzi in Colombia and represents an important epidemiological risk mainly in the central and oriental regions of the country where it occupies sylvatic, peridomestic, and intradomestic ecotopes, and because of this complex distribution, its distribution and abundance could be conditioned by environmental factors. In this work, we explored the relationship between T. dimidiata distribution and environmental factors in the northwest, northeast, and central zones of Colombia and developed predictive models of infestation in the country. The associations between the presence of T. dimidiata and environmental variables were studied using logistic regression models and ecological niche modeling for a sample of villages in Colombia. The analysis was based on the information collected in field about the presence of T. dimidiata and the environmental data for each village extracted from remote sensing images. The presence of Triatoma dimidiata (Latreille, 1811) was found to be significantly associated with the maximum vegetation index, minimum land surface temperature (LST), and the digital elevation for the statistical model. Temperature seasonality, annual precipitation, and vegetation index were the variables that most influenced the ecological niche model of T. dimidiata distribution. The logistic regression model showed a good fit and predicted suitable habitats in the Andean and Caribbean regions, which agrees with the known distribution of the species, but predicted suitable habitats in the Pacific and Orinoco regions proposing new areas of research. Improved models to predict suitable habitats for T. dimidiata hold promise for spatial targeting of integrated vector management.     

Comparative Field Trial of Alternative Vector Control Strategies for Non-Domiciliated Triatoma dimidiata

Chagas disease is a major vector-borne disease, and regional initiatives based on insecticide spraying have successfully controlled domiciliated vectors in many regions. Non-domiciliated vectors remain responsible for a significant transmission risk, and their control is a challenge. We performed a proof-of-concept field trial to test alternative strategies in rural Yucatan, Mexico. Follow-up of house infestation for two seasons following the interventions confirmed that insecticide spraying should be performed annually for the effective control of Triatoma dimidiata; however, it also confirmed that insect screens or long-lasting impregnated curtains may represent good alternative strategies for the sustained control of these vectors. Ecosystemic peridomicile management would be an excellent complementary strategy to improve the cost-effectiveness of interventions. Because these strategies would also be effective against other vector-borne diseases, such as malaria or dengue, they could be integrated within a multi-disease control program.     

The impact of vector control on Triatoma dimidiata in the Guatemalan department of Jutiapa

In 2000, a national control operation against the triatomine vectors of Trypanosoma cruzi, based on house spraying with residual pyrethroid insecticides, was initiated in Guatemala. The impact of the operation against Triatoma dimidiata in the most heavily infested department, Jutiapa, was evaluated by pre- and post-spraying surveys of the vector populations. Of the houses checked for Tri. dimidiata in the baseline surveys, 18.3% were found to be infested with the bug, and in 12.1% of the villages investigated more than half of the houses were found to be infested. The later survey was conducted after 24,250 houses and their associated peridomestic structures (in the 336 villages in which >5% of the houses had been found infested in the pre-spraying survey) had been sprayed. As a result of just this one round of spraying, the mean percentage of houses found infested in each of the villages surveyed twice fell from 36.0% to 8.9%. After the spraying, the percentage of houses infested in each sprayed village was never >50%, and the houses in 35.2% of the sprayed villages that were re-surveyed appeared to have been completely cleared of triatomine bugs. Re-infestation and colonization were mainly observed inside the houses, probably indicating that some indoor bugs survived the spraying round. If the department of Jutiapa is to be freed and kept free from domestic infestation, the efficacy of the insecticide spraying needs to be improved, spraying techniques need to be reviewed, and insecticides need to be re-applied at regular intervals. An effective vector-surveillance system (preferably one in which community participation is encouraged) is also essential.     

Impact of community-based vector control on house infestation and Trypanosoma cruzi infection in Triatoma infestans, dogs and cats in the Argentine Chaco

The relative impact of two community-based vector control strategies on house infestation by Triatoma infestans and Trypanosoma cruzi infection in bugs, domestic dogs and cats was assessed in two neighboring rural areas comprising 40 small villages and 323 houses in one of the regions most endemic for Chagas disease in northern Argentina. The prevalence and abundance of domestic infestation were 1.5- and 6.5-fold higher, respectively, in the area under pulsed, non-supervised control actions operating under the guidelines of the National Vector Control Program (NCVP) than in the area under sustained, supervised surveillance carried out jointly by the UBA research team and NCVP. The prevalence of infestation and infection varied widely among village groups within each area. In the pulsed control area, the prevalence of infection in bugs, dogs and cats was two- to three-fold higher than in the area under sustained surveillance, most of the infected animals qualified as autochthonous cases, and evidence of recent transmission was observed. Infection was highly aggregated at the household level and fell close to the 80/20 rule. Using multiple logistic regression analysis clustered by household, infection in dogs was associated positively and significantly with variables reflecting local exposure to infected T. infestans, thus demonstrating weak performance of the vector surveillance system. For high-risk areas in the Gran Chaco region, interruption of vector-mediated domestic transmission of T. cruzi requires residual insecticide spraying that is more intense, of a higher quality and sustained in time, combined with community participation and environmental management measures.     

Peridomicilary habitat and risk factors for Triatoma infestation in a rural community of the Mexican occident

An examination of peridomestic area organization and triatomine collection in an endemic village for Chagas disease (Jalisco State) identified the habitat of Triatoma longipennis (dominant species) and the risk factors of peridomestic infestation. In 100 visited peridomestic areas, 369 structures (permanent, temporary, and natural) were submitted to active manual research of triatomines. Storage shelters had a higher infestation of T. longipennis than piles of brick and tile; baked clay material had higher degrees of infestation than others. The secondary species Triatoma barberi shares a wide range of peridomicilary habitats with T. longipennis. Peridomestic area infestation risks (evaluated with multivariate logistic regression analysis) are number of closed storage shelters, number of brick and tile piles, number of houses per peridomestic areas, and distance of peridomicile from natural environment. Because both species present great adaptability to different artificial habitats, strategies of control must involved improving the overall management of peridomestic areas to prevent stable colonization.     

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.     

Chromosomal variation and genome size support existence of cryptic species of Triatoma dimidiata with different epidemiological importance as Chagas disease vectors

The wide geographical distribution of Triatoma dimidiata, one of the three major vectors of Chagas disease, ranges from Mexico to northern Peru. Since this species occupies a great diversity of artificial and natural ecotopes, its eradication is extremely difficult. In order to assist control efforts, we used chromosome analyses and DNA amount as taxonomic markers to study genetic variability in populations of T. dimidiata from Mexico, Guatemala, El Salvador and Colombia. We differentiated three groups or cytotypes defined by characteristic chromosome C-banding patterns and genome size measured by flow cytometry. The three cytotypes are restricted to different geographic locations. Cytotype 1 occurs in Mexico (excluding Yucatán), Guatemala (excluding Petén), El Salvador and Colombia. Cytotype 2 occurs in Yucatán and cytotype 3 occurs in Petén. Cytotype 1, commonly associated with domestic and peridomestic environments but also inhabiting sylvatic ecotopes, is the most widespread and with major epidemiological significance. In contrast, the Yucatán cytotype inhabits wild ecotopes but increasingly enters houses, while the Petén cytotype appears exclusively sylvatic. We suggest that these cytotypes represent cryptic species of T. dimidiata with different epidemiological relevance as Chagas disease vectors. Poor ability to colonize human dwellings, together with their restricted geographic distribution, indicate that the Yucatán and Petén putative species probably have much less epidemiological significance than cytotype 1. Thus, the genetic markers we describe are powerful tools to differentiate cryptic species in T. dimidiata with different epidemiological significance, contributing to planning the most effective control measures.     

广东省首次红带锥蝽分布调查与分析

目的 了解红带锥蝽在广东省的地理分布、形态学特征和分子生物学特征。方法 选取粤西地区和珠江三角洲地区8 个地市共23 个县(市、区)开展调查,采取光诱法和人诱法进行搜捕。对捕获的锥蝽进行形态学和分子生物学鉴定,提取锥蝽基因组DNA,PCR 扩增细胞色素b(Cytb)基因,测序并进行序列比对。结果 调查共捕获红带锥蝽273 只,其中若虫36 只,成虫237 只,分布在广东省的8 个地市共23 个县(市、区)。经形态学特征和基因序列分析,采集到的锥蝽为红带锥蝽,与广西合浦红带锥蝽Cytb 基因(GenBank: MH368018. 1)序列同源性最高,为94. 91%。调查共收集到9 起锥蝽叮咬人的事件报告。结论 红带锥蝽广泛分布于广东省粤西地区和珠三角地区,居民被叮咬的事件时有发生,应加强对红带锥蝽的监测和控制。     

家鼠人兽共患寄生虫病的流行与分布

家鼠分布广泛、活动性强, 可传播流行多种人兽共患寄生虫病, 严重影响人类健康。通过对相关资料进行研究, 明确主要的鼠传人兽共患寄生虫和储存宿主, 尤其是掌握对人类危害较大的家鼠所传播的寄生虫种类、病原学和分子生物学特征, 将对防控鼠传人兽共患寄生虫病提供有益资料。