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.

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.