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.

Panzera F ，Ferrandis I ，Ramsey J ，Ordòñez R ，Salazar-Schettino PM ，Cabrera M ，Monroy MC ，Bargues MD ，Mas-Coma S ，O'Connor JE ，Angulo VM ，Jaramillo N ，Cordón-Rosales C ，Gómez D ，Pérez R ... -  《TROPICAL MEDICINE & INTERNATIONAL HEALTH》

Genetic structure of sylvatic, peridomestic and domestic populations of Triatoma dimidiata (Hemiptera: Reduviidae) from an endemic zone of Boyaca, Colombia.

Randomly amplified polymorphic DNA (RAPD) technique was used to study the genetic structure of sylvatic, peridomestic and domestic populations of Triatoma dimidiata. The genetic flow among them was calculated to establish the epidemiological risk of non-domiciliated populations in the transmission of Chagas disease in an endemic area of Boyaca, Colombia. A total of 83 adult specimens were studied: 26 sylvatic, 27 peridomestic and 30 domestic insects. Wright's Fst was 0.071 and the effective migration rate (Nm) 3.3, suggestive of low genetic differentiation and a movement of at least three insects per generation. The calculated percentage of polymorphic loci was 99%, confirming a large average heterozygosity due to a permanent contact between insects of the three populations. These results imply that non-domiciliated populations of T. dimidiata represent an epidemiological risk in the transmission of Chagas disease owing to the fact that they can colonize human dwellings. Close surveillance of non-strictly domiciliated species of triatomines such as T. dimidiata should entail not only the domicile but also the peridomicile and should include control programs of animal reservoirs. Houses enhancement, educational programs, surveillance of reinfestation and of individuals at risk of infection should be priorities in the control policies in endemic regions such as Boavita, Boyaca.

Ramírez CJ ，Jaramillo CA ，del Pilar Delgado M ，Pinto NA ，Aguilera G ，Guhl F ... -  《ACTA TROPICA》

Two distinct Triatoma dimidiata (Latreille, 1811) taxa are found in sympatry in Guatemala and Mexico.

Approximately 10 million people are infected with Trypanosoma cruzi, the causative agent of Chagas disease, which remains the most serious parasitic disease in the Americas. Most people are infected via triatomine vectors. Transmission has been largely halted in South America in areas with predominantly domestic vectors. However, one of the main Chagas vectors in Mesoamerica, Triatoma dimidiata, poses special challenges to control due to its diversity across its large geographic range (from Mexico into northern South America), and peridomestic and sylvatic populations that repopulate houses following pesticide treatment. Recent evidence suggests T. dimidiata may be a complex of species, perhaps including cryptic species; taxonomic ambiguity which confounds control. The nuclear sequence of the internal transcribed spacer 2 (ITS2) of the ribosomal DNA and the mitochondrial cytochrome b (mt cyt b) gene were used to analyze the taxonomy of T. dimidiata from southern Mexico throughout Central America. ITS2 sequence divides T. dimidiata into four taxa. The first three are found mostly localized to specific geographic regions with some overlap: (1) southern Mexico and Guatemala (Group 2); (2) Guatemala, Honduras, El Salvador, Nicaragua, and Costa Rica (Group 1A); (3) and Panama (Group 1B). We extend ITS2 Group 1A south into Costa Rica, Group 2 into southern Guatemala and show the first information on isolates in Belize, identifying Groups 2 and 3 in that country. The fourth group (Group 3), a potential cryptic species, is dispersed across parts of Mexico, Guatemala, and Belize. We show it exists in sympatry with other groups in Peten, Guatemala, and Yucatan, Mexico. Mitochondrial cyt b data supports this putative cryptic species in sympatry with others. However, unlike the clear distinction of the remaining groups by ITS2, the remaining groups are not separated by mt cyt b. This work contributes to an understanding of the taxonomy and population subdivision of T. dimidiata, essential for designing effective control strategies.

Dorn PL ，Calderon C ，Melgar S ，Moguel B ，Solorzano E ，Dumonteil E ，Rodas A ，de la Rua N ，Garnica R ，Monroy C ... -  《PLoS Neglected Tropical Diseases》

Identification of a large hybrid zone between sympatric sibling species of Triatoma dimidiata in the Yucatan peninsula, Mexico, and its epidemiological importance.

Triatoma dimidiata is one of the major Chagas disease vectors, with an extensive diversity in its morphology, habitat, and level of domiciliation. Molecular studies based on the internal transcribed spacer 2 (ITS-2) have subdivided this species into four potential taxonomic groups. Using both ITS-2 and cytochrome B markers, we confirmed the sibling species status of ITS-2 Group 3 and detected an apparent sympatry of ITS-2 Groups 2 and 3 in the Yucatan peninsula, Mexico. Here we examine the geographic distribution of T. dimidiata ITS-2 genotypes in the region and compare their egg production and Trypanosoma cruzi infection rates, as indicators of biological differences between groups. PCR genotyping of large natural populations showed an extensive sympatry of Groups 2 and 3 in most of the peninsula, often within the same house. We also detected a large proportion of individuals displaying ITS-2 sequences from both Groups 2 and 3, suggesting hybridization. Analysis of ITS-2 genotype frequencies indicated a strong departure from Hardy-Weinberg equilibrium in female hybrids, but not in males, due to a large heterozygote deficit. These results suggest random mating between ITS-2 Groups 2 and 3 combined with reduced viability and/or survival in female hybrids. This and other factors may allow for the maintenance of distinct ITS-2 Groups 2 and 3 populations despite high hybrid frequencies. Importantly, T. cruzi infection was much higher in hybrids compared to ITS-2 Groups 2 and 3 individuals, but all three genotypes appeared to seasonally infest houses in a similar manner in the region. These findings warrant further studies on T. dimidiata taxonomy and its epidemiologic implications.

Herrera-Aguilar M ，Be-Barragán LA ，Ramirez-Sierra MJ ，Tripet F ，Dorn P ，Dumonteil E ... -  《-》

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.

Dumonteil E ，Tripet F ，Ramirez-Sierra MJ ，Payet V ，Lanzaro G ，Menu F ... -  《AMERICAN JOURNAL OF TROPICAL MEDICINE AND HYGIENE》