Identification and characterization of microsatellite markers for population genetic studies of Panstrongylus megistus (Burmeister, 1835) (Triatominae: Reduviidae)

Occurrence and distribution of Panstrongylus megistus (Burmeister, 1835) (Hemiptera, Reduviidae) in a metropolitan area of Southern Brazil

Two triatomine genera (Panstrongylus and Triatoma) have essentially been recorded in Rio Grande do Sul State, Brazil. Panstrongylus megistus should be highlighted since this species is one of the main vectors of Trypanosoma cruzi in Brazil, due to its wide geographical distribution and the high susceptibility to this protozoan. This study aimed to present not only the occurrence and distribution of P. megistus in the Porto Alegre city's metropolitan area (PAMA), Rio Grande do Sul State, Brazil, but also the rates of T. cruzi infection, from 2009 to 2020. The PAMA, which comprises 34 cities and 4.4 million habitants, extends across the transition area in two biomes - Pampa and Mata Atlantica - found in the state. Results showed that P. megistus was recorded in 76.5% of cities (i.e., 26 out of 34), mainly in Porto Alegre city, where the vector was found in 11 out of the 12 years that were monitored. Three hundred and nineteen specimens were captured. Two hundred and sixty-seven specimens (83.7%) were located intradomicile (p < 0.0001), while 52.3% positivity for T. cruzi was found. Thus, P. megistus is important in the PAMA, because it invades and colonizes the households. Moreover, the high rates of T. cruzi infection have drawn attention.

Dynamics of Panstrongylus megistus infestation,the primary vector of Trypanosoma cruzi in Minas Gerais,Brazil

Panstrongylus megistus is considered one of the primary species of epidemiological importance for the transmission of Chagas disease in Brazil due to its wide geographical distribution throughout the national territory, good ability to invade and colonize houses, and high rates of natural infection by the Trypanosoma cruzi. The importance of this species in Minas Gerais has been recognized since the 80s. It is responsible for the high prevalence rates of Chagas disease in the west of the state. Studies conducted in the municipality of Jaboticatubas show that P. megistus is still the most captured vector in the region, even after 40 years of uninterrupted actions of the Chagas Disease Control Program in the municipality. Despite the importance of the species, its population dynamics is little studied. Consequently, crucial genetic information such as genetic diversity and gene flow among environments have not been well characterized yet. In this context, this work presents a population genetic analysis at the microgeographic level using microsatellite markers in samples of P. megistus obtained from Jaboticatubas to better understand the infestation dynamics of the primary vector species of T. cruzi in the region. The observed and expected heterozygosity ranged from 0.26 to 0.47 and 0.47 to 0.65, respectively. Most loci presented Hardy-Weinberg disequilibrium due to the excess of homozygotes. The pairwise Fst ranged from 0.05 to 0.35, with the p-value significant for all comparisons, indicating the absence of gene flow between them. The values of Fis found ranged from 0.25 to 0.52, all values of p ≤ 0.05, probably due to structured populations, inbreeding, or null alleles. The results suggest an extended stay of this species in the colonized environments, with rare dispersal to other locations. Such results differ from that observed for Triatoma brasiliensis and Triatoma dimidiata, species that present constant movement, even after colonization of the artificial environment, and are similar to the behavior of Triatoma infestans. Thus, the study reinforces the importance of continuous entomological surveillance in the areas of occurrence of P. megistus to avoid the installation and formation of new foci of household infestation in the region.