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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.

In this study, we evaluated the responses of Triatoma dimidiata Latreille (Hemiptera: Reduviidae) to volatiles emitted by conspecific females, males, mating pairs and metasternal gland (MG) extracts with a Y-tube olfactometer. The volatile compounds released by mating pairs and MGs of T. dimidiata were identified using solid-phase microextraction and coupled gas chromatography-mass spectrometry (GC-MS). Females were not attracted to volatiles emitted by males or MG extracts; however, they preferred clean air to their own volatiles or those from mating pairs. Males were attracted to volatiles emitted by males, females, mating pairs, pairs in which the male had the MG orifices occluded or MG extracts of both sexes. However, males were not attracted to volatiles emitted by pairs in which the female had the MG orifices occluded. The chemical analyses showed that 14 and 15 compounds were detected in the headspace of mating pairs and MG, respectively. Most of the compounds identified from MG except for isobutyric acid were also detected in the headspace of mating pairs. Both females and males were attracted to octanal and 6-methyl-5-hepten-2-one, and males were attracted to 3,5-dimethyl-2-hexanol. Males but not females were attracted to a seven-compound blend, formulated from compounds identified in attractive MG extracts.

Summary 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 Yucatan), Guatemala (excluding Peten), El Salvador and Colombia. Cytotype 2 occurs in Yucatan and cytotype 3 occurs in Peten. 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 Yucatan cytotype inhabits wild ecotopes but increasingly enters houses, while the Peten 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 Yucatan and Peten 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. La vaste distribution geographique de Triatoma dimidiate, un des trois principaux vecteurs de la maladie de Chagas, sevi de Mexico au nord du Perou. Parce que cette espece occupe une grande diversite d'habitat compose de terrain artificiel et d'ecotopes naturels, son eradication est extremement difficile. Dans le but de contribuer aux efforts de controle, nous avons utilise des analyses chromosomiques et les quantites d'ADN comme marqueurs taxonomiques pour etudier la variabilite genetique dans les populations de T. dimidiate de Mexico, Guatemala, Salvador et Colombie. Nous avons distingue trois groupes ou cytotypes definis par les profils caracteristiques en bandes C du chromosome et la taille du genome mesuree par flow cytometrie. Les trois cytotypes sont confines dans des locations geographiques differentes. Le cytotype 1 sevi a Mexico (a l'exception du Yucatan), au Guatemala (a l'exception de Peten), au Salvador et en Colombie. Le cytotype 2 sevi dans le Yucatan et le cytotype 3 a Peten. Le cytotype 1, communement associea l'environnement domestique et peri domestique mais aussi a des ecotopes sylvatiques habites, est le plus prevalant avec une epidemiologie majeure significative. Par contre, le cytotype du Yucatan sevi dans les ecotopes sauvages mais de plus en plus entre dans les maisons, alors que le cytotype de Peten semble etre essentiellement sylvatique. Nous suggerons donc que ces cytotypes representent des especes cryptiques de T. dimidiate avec differentes importances epidemiologiques en tant que vecteurs de la maladie de Chagas. Le peu d'habilitea coloniser les habitations humaines ainsi que leur distribution geographiques restreintes indiquent que les putatives especes du Yucatan et de Peten ont probablement peu de signification epidemiologique par rapport au cytotype 1. Les marqueurs genetiques que nous decrivons sont donc de puissants outils pour differencier des especes cryptiques de T. dimidiate, pouvant ainsi contribuer a planifier des mesures de controle plus efficaces. La amplia distribucion del Triatoma dimidiata, uno de los tres vectores principales de la enfermedad de Chagas, se extiende desde Mejico al norte de Peru. Puesto que esta especie ocupa una gran diversidad de ecotopos artificiales y naturales, su erradicacion es extremadamente dificil. Con el fin de ayudar en los esfuerzos de control, utilizamos el analisis cromosomico y la cantidad de ADN como marcadores taxonomicos para estudiar la variabilidad genetica en poblaciones de T. Dimidiata provenientes de Mejico, Guatemala, El Salvador y Colombia. Diferenciamos tres grupos o citotipos, definidos por bandeo cromosomico y patron de bandas C caracteristicos y por el tamano de su genoma, medido por citometria de flujo. Los tres citotipos estaban restringidos a diferentes areas geograficas. El citotipo 1 ocurria en Mejico (excluyendo Yucatan), Guatemala (excluyendo Peten), El Salvador y Colombia. El citotipo 2 ocurria en Yucatan y el citotipo 3 en Peten. El citotipo 1, comunmente asociado con ambientes domesticos y peridomesticos, pero que tambien habita ecotipos selvaticos, es el mas extendido y el que mayor significado epidemiologico tiene. En contraste, el citotipo de Yucatan habita ecotopos salvajes, pero cada vez con mayor frecuencia entra en las casas, mientras que el citotipo Peten es exclusivamente selvatico. Sugerimos que estos citotipos representan la especie criptica de T. Dimidiata con diferente relevancia epidemiologica como vectores de la enfermedad de Chagas. Su escasa habilidad para colonizar viviendas humanas, junto con su distribucion geografica restringida, indican que las especies putativas de Yucatan y Peten probablemente tienen un significado epidemiologico muchisimo menor que el citotipo 1. Por lo tanto, los marcadores geneticos que describimos son herramientas poderosas para diferenciar entre especies cripticas de T. dimidiata, contribuyendo a planear medidas de control mas efectivas.

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 (Stahl) 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.

Scorpion stings cause more morbidity in Mexico than any other country, leading to about 100 deaths annually. In 1999, the State of Morelos reported nine deaths among 30663 cases of scorpion sting. To replace lindane used for scorpion control, field trials of pyrethroid pesticides were undertaken in Morelos during 1998-2000 at the village of Chalcatzingo (population initially with 2760 inhabitants and 530 houses). Pre-intervention surveys detected scorpions (Scorpiones: Buthidae) of two species in the majority of houses: Centruroides limpidus limpidus Karsch outnumbering Vaejovis mexicanus smithi Koch. Scorpion prevalence was assessed, pre- and post-spray, directly by searching (40 min/house) and by householder reports of sightings inside houses. Pre-intervention perceptions of scorpion abundance were similar for all areas, with sightings in 12-18% of houses, whereas daytime searches detected more infestations in eastern parts of the village (prevalence 17% indoors, 22% outdoors) than in other sectors (9% indoors, 14% outdoors). Pyrethroids were evaluated as residual treatments in separate sectors of Chalcatzingo, with almost complete coverage indoors and peridomestically, using the following four formulations: bifenthrin 10% wettable powder (WP) applied at 50mg a.i./m2, cyfluthrin 10% WP (Solfac 10 WP) at 44-55 mg a.i./m2, deltamethrin 2.5% suspension concentrate (Biothrin 25 SC) at 11 mg a.i./m2 and 5% WP (K-Othrine 50 WP) at 35 mg a.i./m2. Phase 1 compared bifenthrin 10 WP, Solfac 10 WP and Biothrin 25 SC sprayed in December 1998; phase 2 compared Solfac 10 WP and K-Othrine 50 WP sprayed in June and again in December 2000, with follow-up surveys of scorpions one month post-spray and subsequently. Scorpion prevalence was reduced by 64-77% peridomestically one month post-spray and by 83, 46 and 15% in houses sprayed with cyfluthrin WP, bifenthrin WP or deltamethrin SC, respectively. Householder reports of sighting scorpions indoors were 33-85% below pre-intervention levels. Cumulative effects of the three spray-rounds over 3 years reduced scorpion prevalence by approximately 60% in the deltamethrin WP re-sprayed area and by approximately 90% in the cyfluthrin WP re-sprayed area. Householder sightings also fell by 67 and 28% in the cyfluthrin and delta-methrin re-sprayed areas, respectively. Operational efficacy of these products against scorpions at the dosages applied was ranked as cyfluthrin WP > bifenthrin WP > deltamethrin SC > WP. Reported cases of scorpion sting intoxication fell by 17% during this study after having risen by approximately 40% over four previous years.

Mexico has 18 species of Triatomine bugs (Hemiptera: Reduviidae) reported to be vectors of Trypanosoma cruzi. Chagas Disease is widespread in Mexico, with up to 3.5% seropositivity of human transfusion blood. The State of Oaxaca has the longest history of endemic Chagas Disease, based on acute and chronic case reports, and of entomological surveys in the country. However, the State health care services need more information on current risks of vector transmission. In order to identify and characterize areas of transmission in Oaxaca and to stratify the vector potential, the distribution of domestic Triatominae was surveyed during 1996-98 in collaboration with the primary health care services and local communities. Villages were studied in 11% of 570 municipalities in Oaxaca. Eight triatomine species were found in domestic and peri-domestic habitats: Triatoma barberi Usinger, T. bolivari Carcavallo et al., T. dimidiata (Latreille), T. mazzottii Usinger, T. nitida Usinger, T. pallidipennis (Stal), T. phyllosoma (Burmeister) and Rhodnius prolixus Stal. For each triatomine species in Oaxaca, the range of distribution and habitat characteristics are described. Habitat partitioning, principally based on altitude and mean annual precipitation, limited the overlap of distribution between species. Relatively consistent altitude of human settlements facilitates the dispersion of individual species within microregions. Entomological indices of house infestation were used to estimate that approximately 50% of the human population (1,874,320 inhabitants) would be at risk of vector transmission, with a minimum of 134,320 infected people and 40,280 chronic cases of Chagas Disease currently in Oaxaca.