We reported a systematic collection of adults, nymphs, and eggs of T. williami inside human dwellings from Barra do Garças, Mato Grosso, Brazil, during two different years. In the second year, we found nymphs in the last developmental stage, suggesting early stages in the domestication of this sylvatic species. The domiciliation of wild triatomine species is a risk factor for reestablishing the vectorial transmission of ChD (SILVEIRA and DIAS, 2011; WALECKX et al. 2015). Surveillance for species, considering the domiciliation principle and the development of actions to interrupt this process, is paramount in preventing ChD. For Berenger and Pages (2007), the process of domestication seems irreversible.
Lunardi et al. (2017) discussed that morphological plasticity in the shape of T. williami is associated with blood source, but they did not test whether plasticity confers a fitness advantage to culminate in domiciliation by this species. However, in a previous study, Lunardi et al. (2015) recorded a high potential vector for nymphs of this species.
So far, T. williami has been considered a secondary T. cruzi vector because it maintains its wild condition and shows synanthropic potential, colonizing peridomiciles and, frequently, invading households. The synanthropy represents a secondary adaptation by sylvatic species in response to environmental changes. Such adaptability to human dwellings depends on triatomine plasticity (FORATTINI, 1980).
Given the increasing importance of secondary triatomine species and their frequency of occurrence within domiciliary environments, further eco-epidemiological studies should be stimulated to monitor changes in the behavior of these species. The behavioral characteristics of the different species of triatomines allow them to adapt to environmental changes, directly reflecting the population dynamics of these vectors. Thus, natural or anthropogenic environmental factors interfere with species density, dispersal, reproduction, and domiciliation (VAZQUEZ-PROKOPEC et al., 2006; GRIJALVA et al., 2014; CORASSA et al., 2016; VIANNA et al., 2017).
The first T. williami specimen in Nova Xavantina, Mato Grosso, Brazil, was recorded by Travassos-Filho (1972). This specimen was collected inside the house of a worker and was infected by T. cruzi. Then, Arrais-Silva et al. (2011) and Andrade-Neto (2012), using molecular biology, found that the natural infection rate of this species by T. cruzi was 30% in Barra do Garças, Mato Grosso, Brazil. In our parasitological feces diagnosis, we observed an elevated infection rate of T. williami by T. cruzi in 2019 and 2020, indicating the transmission risk of the parasite by this vector.
The finding of the TcIV DTU of T. cruzi in T. williami collected in the home is an unprecedented record for Mato Grosso, Brazil, and it is concerning. The distribution of DTU TcIV is more significant in Central and South America, with greater density in the Amazon region. In the Western Brazilian Amazon region, this is the leading cause of human infections, resulting from oral transmission outbreaks of the parasite in the region (MONTEIRO et al., 2012; TESTON et al., 2017; SANTANA et al., 2019). The origin of this DTU is derived as a wild cycle, but studies have already demonstrated its participation in domestic cycles (ZINGALES et al., 2012; BRENIÈRE et al., 2016), which are frequently correlated to acute ChD infections in humans. Studies analyzing triatomines from different biomes have not recorded this DTU for the Cerrado (BARROS et al., 2017). Therefore, this unprecedented record for Cerrado, the predominant biome in our study area. Izeta-Alberdi et al. (2016) found no correlation between TcIV and any vector species. Barros et al. (2017) found a predominance of this DTU for the Triatoma genus, corroborating the record of our study of this strain in T. williami. Regarding the potential reservoirs that participate in the transmission cycle of this parasite, the main mammals are carnivores, primates, and rodents (ZINGALES et al., 2012; IZETA-ALBERDI et al., 2016; BARROS et al., 2017).
The characteristics found for T. williami seem similar to those of T. infestans. According to Vinhaes et al. (2014), the protagonism of T. infestans can be justified due to its high degree of anthropophily, a large capacity to colonize human domiciles, and high rates of natural infection. The record of T. williami in the domiciliation process lights up an alert because there is a record of this species naturally infected by T. cruzi, with a high infection rate.
It is necessary to carry out immediate intervention measures to interrupt this process of domiciliation of T. williami in the urban area of Barra do Garças, Mato Grosso, Brazil. The approximation of vectors with human living spaces increases the risk of transmission of Chagas disease (CARVALHO and GOMES, 2014).
When we analyzed the records of the locations with triatomines in Barra do Garças over ten years, we identified a higher occurrence in households in the four neighborhoods bordering PESA. Thus, the presence of a green belt associated to the artificial light of these households might be supporting and promoting dispersion of the triatomines. Martins et al. (2019) reported that Barra do Garças, Mato Grosso, has a different ecological context, given its proximity to PESA. This state park may facilitate human contact with wild triatomines, which are potential vectors of ChD, especially in PESA neighborhoods.
The occurrence of wild triatomine species sporadically invading human houses is a significant difficulty in vector surveillance programs (CARANHA et al., 2011). A study in a similar area, by Jácome-Pinilla et al. (2015), proved an actively dispersing area and triatomines highly attracted to artificial lights. Furthermore, the environmental parameters encountered during this study, particularly during the first hours after sunset, are favorable for the active dispersal of sylvatic triatomines. One immediate recommendation is that external artificial lights on walls must remain turned off during the first hours after sunset, the period when most sylvatic triatomines find favorable atmospheric and environmental conditions for dispersal.
Entomological surveillance for triatomines in Barra do Garças has been done mainly by the population, showing the importance of passive surveillance by residents to detect foci of the triatomines. Thus, we reinforce the importance of health education for ChD prevention. The passive surveillance improved risk management by the city health system, favoring timely intervention in the ChD transmission chain. This process corroborates that entomological surveillance has been supported by community referees responsible for the Triatomine Information Post Network (IPN), which has been established for a long time (SILVEIRA and DIAS, 2011). The knowledge of the population about triatomines and ChD is paramount to promoting collaboration in vector control and reducing vector transmission (VILLELA et al., 2009a, 2009b; COURA; JUNQUEIRA, 2012). Thus, the better the understanding, the greater the chance of intervening positively, preventing health problems and favoring healthier ways of life (AYRES, 2009).
Analysis of the triatomines collected in Barra do Garças in a historical ten-year series showed earlier demonstrates the increase in vector density in 2019. The results indicate periods with a peak incidence of triatomines in the third quarter of the year. Seasonality is also observed in Chagas vector populations and transmission. In combination with density-dependent regulation, these characteristics have led to the belief that insecticide control of these vectors can be improved if seasonally timed (GORLA, 1988; SCHOFIELD, 1991).
Thus, studies are needed to investigate the mammal fauna and triatomines in urban areas and adjoining neighborhoods of PESA to evaluate the dimensions and degrees of trypanosomal infection. These new studies will allow us to assess the infection risks of humans around the park, considering the presence of the etiological agent of ChD.
The finding of T. williami colonies inside homes and the high rate of natural infection for this species reinforces the need to study reservoirs and their role in maintaining and or dispersing T. cruzi. The main determinants for establishing human infection by T. cruzi involve the adaptation of triatomines to the domicile and peridomicile and the T. cruzi circulation between wild and domestic animals in these environments (COURA, 2007).
However, understanding variation in vector infection prevalence alone is not enough to understand the risk to humans from the vector-related transmission. Several factors affect the relationship between vectors and the prevalence of human infection (BROWNE et al., 2016). The maintenance of sustainable surveillance activities is possible only if all transmission network components are identified (NOIREAU et al., 2009). These measures are essential for the sustainability of the control of ChD, since the re-infestation of homes by native triatomines occurs continuously, and as there are wild foci of vector species of T. cruzi, there is a risk of infection of the reservoirs (PRIOTTO, 2012).
The detection of possible triatomine domiciliation in the urban area of Barra do Garças, Mato Grosso, Brazil, demonstrates the importance of entomological surveillance and underscores the importance of strengthening prevention programs and controlling ChD infections. Our results reinforce the importance of and need for entomological surveillance in routine home visits by health field agents. Therefore, maintaining and systematizing chemical control measures and following the Brazilian Ministry of Health protocol and environmental management in households to reduce the risk of ChD infection in endemic areas of the state of Mato Grosso, Brazil, is of utmost importance.