Urban vectors of Chagas disease in the American continent: A systematic review of epidemiological surveys

Hidden Trypanosoma cruzi foci in Triatoma brasiliensis from a Brazilian Touristic area in the Northeast

This study aimed to assess the risk of human-vector interactions and Trypanosoma cruzi transmission in touristic areas of northeastern Brazil. We analyzed 180 adult Triatoma brasiliensis specimens collected from nine peridomestic and sylvatic ecotopes across the states of Rio Grande do Norte and Paraíba. High T. cruzi infection rates were detected in both ecotopes, indicating sustained parasite circulation. Metabarcoding of blood meals revealed a broader host range than previously documented, including human blood meals in sylvatic touristic areas with high infection rates, raising concerns about vector-mediated transmission in these settings. Given the potential public health implications, our findings were formally communicated to local health and tourism authorities, with specific recommendations to inform and protect visitors in high-risk zones. These results underscore the need for targeted surveillance and vector control strategies in tourist-exposed areas, where interventions must be integrated with efforts to preserve local cultural and ecological heritage.

Human migrations, anthropogenic changes, and insect-borne diseases in Latin America

Rapid urbanization and migration in Latin America have intensified exposure to insect-borne diseases. Malaria, Chagas disease, yellow fever, and leishmaniasis have historically afflicted the region, while dengue, chikungunya, and Zika have been described and expanded more recently. The increased presence of synanthropic vector species and spread into previously unaffected areas due to urbanization and climate warming have intensified pathogen transmission risks. This review examines recent outbreaks and reemergence of insect-borne diseases through five case studies: (i) malaria transmission linked to political instability and large-scale migration through the Amazon jungle; (ii) the expansion of triatomine bug habitats into overcrowded, substandard urban settlements, increasing Chagas disease incidence; (iii) the influence of movement and ecotourism in the Amazonia on yellow fever transmission in peri-urban areas; (iv) the spread of visceral leishmaniasis driven by deforestation and human-canine movement; and (v) dengue outbreaks in rural Amazon regions, spurred by urbanization and rural development. The findings underscore the complex interactions among vectors, pathogens, and shifting environmental and social conditions, complicating predictability and control. Addressing the social, economic, and political determinants of health is crucial to reducing disease transmission. Key measures include scaling vaccine coverage, especially for dengue and yellow fever; developing vaccines and treatments for neglected diseases; improving housing and sanitation; strengthening vector surveillance and control; fostering community engagement; enhancing data-driven interventions.

Unusual frequency of Trypanosoma cruzi DTU TcI and predominance of hybrid lineages in Triatoma infestans before and after control interventions in the Argentinian Chaco

Transmission of Trypanosoma cruzi involves diverse hosts, vectors and parasitic genotypes, in different environments. In recent decades, the distribution of T. cruzi has altered due to urbanization of affected people and vectors. We implemented a longitudinal intervention program between 2015 and 2022 which aimed to suppress (peri)domestic Triatoma infestans in the municipality of Avia Terai (Chaco Province, Argentina), and found a marginal risk of domestic vector-borne transmission across the rural-to-urban gradient after interventions. Here, we identified the parasite Discrete Typing Units (DTUs) in infected T. infestans collected throughout the intervention program (37 insects pre-intervention and 7 post-intervention). Identification of DTUs was conducted by two methodologies, using DNA extracted from T. infestans rectal ampoules. We also assessed the association between blood-feeding sources and DTUs. Complete DTU identification was achieved in 48 % of samples. The hybrid lineages TcV or TcVI and their combinations predominated (72 %), followed by TcI (16 %) and mixed infections of TcI and hybrid lineages (14 %). Half (50 %) of the houses harbored TcI infected bugs either alone or mixed with TcII/TcV/TcVI. Humans predominated as the bloodmeal sources in all insects with identified DTU. All DTUs (TcI, TcV and TcII/TcV/TcVI) were recorded in both rural and peri-urban environments, with 62 % of the houses having more than one DTU. These results confirm the predominance of hybrid lineages in domestic transmission cycles of the Argentine Chaco. However, the finding of several triatomines infected with TcI both pre- and post-intervention raises the question of which host(s) are involved in its transmission.

Eco-epidemiological aspects and risk factors associated with human Chagas disease in rural areas of the state of Piauí, Brazil

BACKGROUND

Piauí is located in Northeastern Brazil, an endemic area for Chagas disease, with the Brazilian semiarid representing the second region in number of people infected by the parasite Trypanosoma cruzi. The state of Piauí is one of the most socially vulnerable territories with direct impact on the access to diagnosis and treatment of Chagas disease for the population living in rural communities. Triatoma brasiliensis is the vector species of greatest epidemiological importance in Northeastern Brazil. We investigated the triatomine fauna and risk factors associated to T. cruzi transmission in two municipalities, Pedro II and Oeiras, located in different mesoregions of Piauí.

METHODS

Twenty-three rural areas were selected for triatomines search and serological survey of the population. The analysis of triatomines consisted on identifying T. cruzi infection index by microscopy and kDNA-PCR followed by parasite genotyping through the use of multilocus PCR to characterize the discrete typing units (DTUS), and the identification of food sources using PCR directed to the 12S rRNA gene of vertebrates and sequencing.

RESULTS

A total of 1,043 triatomines identified as T. brasiliensis, Triatoma pseudomaculata, Rhodnius nasutus, Rhodnius sp. and Panstrongylus lutzi were collected. The overall positivity for T. cruzi was 4.6% and 11.4% by microscopy and kDNA-PCR, respectively. The DTUs TcV (∼ 44%) and TcI (∼ 43%) were the most prevalent in either single or mixed infections. This is the first report of TcV and TcVI infections in vectors of Piauí. The most frequent blood source was Homo sapiens (46.5%), of which ∼ 42% individuals (28/67) were collected indoors and four of them (14.3%) tested positive for T. cruzi kDNA in Pedro II. Chicken (∼ 19%), domestic cat (∼ 17%) and others were also identified as feeding sources for triatomines. Serological survey revealed 2% seroprevalence. Variables as age over 60 years (p = 0.01), Black race (p = 0.002) and occupation as retired (p = 0.004) significantly influenced the seropositivity.

CONCLUSION

Despite the reduced seroprevalence of the population, the epidemiological scenario of Chagas disease in both municipalities highlights the risk of the re-emergence of domestic vector-borne transmission. Ensuring continued entomological surveillance and vector control programs and providing access to diagnosis and treatment for the susceptible population are still needed.

Climate change and Trypanosoma cruzi transmission in North and central America

Trypanosoma cruzi is a protozoan parasite that causes Chagas disease in humans. Transmission of T cruzi by triatomine vectors is dependent on diverse environmental and socioeconomic factors. Climate change, which is disrupting patterns of human habitation and land use, can affect the epidemiology of Chagas disease by influencing the distribution of vector and host species. We conducted a review using triatomine distribution as a proxy for T cruzi transmission in North America (Canada, Mexico, and the USA) and central America (Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama) and investigated the association of T cruzi transmission with climate change, identifying 12 relevant studies. Most studies (n=9) modelled the effect of the scenario of climate change on the distribution of relevant vector species and found that global warming could sometimes favour and sometimes hinder triatomine distribution. There is a need for more research in parasite biology and social sciences to further understand how climate change and socioeconomic factors can affect the epidemiology of this neglected tropical disease.

A simplified molecular tool for detecting the Chagas etiological agent using a vector feces sample in field conditions

Triatomine bugs are vectors of Trypanosoma cruzi, the etiologic agent of Chagas disease in the American continent. Here, we have tested a loop-mediated isothermal amplification (LAMP) test for a direct detection of T. cruzi in feces of Triatoma infestans, the main vector of this parasite in the Southern Cone of America. The analytical evaluation showed positive results with samples of triatomine feces artificially inoculated with DNA from strains of T. cruzi corresponding to each Discrete Typing Units (I-VI), with a sensitivity of up to one parasite per reaction. Conversely, the reaction yielded negative results when tested with DNA from Trypanosoma rangeli and other phylogenetically related and unrelated organisms. In triatomines captured under real field conditions (from urban households), and defined as positive or negative for T. cruzi using the reference microscopy technique, the LAMP test achieved a concordance of 100 %. Our results demonstrate that this LAMP reaction exhibits excellent analytical specificity and sensitivity without interference from the fecal matrix, since all the reactions were conducted without purification steps. This simple molecular diagnostic technique can be easily used by vector control agencies under field conditions.

The mlpt smORF gene is essential for digestive physiology and molting during nymphal stages in the kissing bug Rhodnius prolixus

Chagas disease affects around 8 million people globally, with Latin America bearing approximately 10,000 deaths each year. Combatting the disease relies heavily on vector control methods, necessitating the identification of new targets. Within insect genomes, genes harboring small open reading frames (smORFs - < 100 amino acids) present numerous potential candidates. In our investigation, we elucidate the pivotal role of the archetypal smORF-containing gene, mille-pattes/polished-rice/tarsalless (mlpt/pri/tal), in the post-embryonic development of the kissing bug Rhodnius prolixus. Injection of double-stranded RNA targeting mlpt (dsmlpt) during nymphal stages yields a spectrum of phenotypes hindering post-embryonic growth. Notably, fourth or fifth stage nymphs subjected to dsmlpt do not undergo molting. These dsmlpt nymphs display heightened mRNA levels of JHAMT-like and EPOX-like, enzymes putatively involved in the juvenile hormone (JH) pathway, alongside increased expression of the transcription factor Kr-h1, indicating changes in the hormonal control. Histological examination reveals structural alterations in the hindgut and external cuticle of dsmlpt nymphs compared to control (dsGFP) counterparts. Furthermore, significant changes in the vector's digestive physiology were observed, with elevated hemozoin and glucose levels in the posterior midgut of dsmlpt nymphs. Importantly, dsmlpt nymphs exhibit impaired metacyclogenesis of Trypanosoma cruzi, the causative agent of Chagas disease, underscoring the crucial role of proper gut organization in parasite differentiation. Thus, our findings constitute the first evidence of a smORF-containing gene's regulatory influence on vector physiology, parasitic cycle, and disease transmission.

Circulation of Trypanosoma cruzi in triatomines and Didelphis sp. in urban areas: Transmission risk assessment in the Metropolitan Region

The presence of Trypanosoma cruzi vectors in urban areas has been frequent, with colonization of homes and associated with reservoir animals that increase risk to humans, with simultaneous circulation of vectors and T. cruzi. The study aimed to describe the circulation of triatomines and T. cruzi in the Metropolitan Region of São Paulo, as well as evaluate risk situations. For analysis purposes, the triatomine notification information from January 2016 to July 2023 was used. While for Didelphis sp. collection with the aid of traps, notification information used was from 2019 to 2023. Information about triatomines came from spontaneous demand by the population and notification services were carried out by state field teams following defined protocols. 202 notifications were received with the capture of 448 triatomines. The positivity for T. cruzi observed was 60.5%. Regarding Didelphis sp., 416 animals were collected, 5.3% of which were positive for T. cruzi. There was overlapping areas of presence of infected triatomines and Didelphis sp., whose Discrete Typing Unit (DTU) was T. cruzi I. This work indicates the presence of infected vectors in urban areas, and the presence of a wild cycle of T. cruzi in didelphiids, reaffirming the need for and importance of vector surveillance work, through actions that can prevent the transmission of Chagas disease.

Interesting case from Argentina: Kidney transplant recipient with skin lesions-A Latin American perspective

This is a case of a kidney transplant recipient who presented with skin lesions, low-grade fevers, and pancytopenia 2 months after his transplant.

Population genetics and genomics of Triatoma brasiliensis (Hemiptera, Reduviidae) in an area of high pressure of domiciliary infestation in Northeastern Brazil

Understanding the population dynamics of vectors is crucial for effective control of vector-borne diseases. In the Northeastern Brazilian semi-arid region, Triatoma brasiliensis persists as the most significant Chagas disease vector, frequently displaying recurrent domiciliary infestations. This situation raises relevant public health concerns in the municipality of Currais Novos in the state of Rio Grande do Norte. This area has experienced a high prevalence of peridomiciliary re-infestations by T. brasiliensis, coupled with elevated rates of Trypanosoma cruzi infection. Therefore, we assessed the distribution of genetic variation via mitochondrial Cytochrome b gene (MT-CYB) sequencing (n = 109) and single nucleotide polymorphisms (SNPs, n = 86) to assess the gene flow among distinct populations distributed in varied geographic spots and environments, mainly sylvatic and peridomiciliary. Insects were collected from rural communities at Currais Novos, enclosed within a 16 km radius. Sampling included 13 populations: one intradomiciliary, eight peridomiciliary, and four sylvatic. Furthermore, an external population located 220 km from Currais Novos was also included in the study. The method employed to obtain SNP information relied on ddRAD-seq genotyping-by-sequencing (GBS), enabling a genome-wide analysis to infer genetic variation. Through AMOVA analysis of MT-CYB gene variation, we identified four distinct population groups with statistical significance (FCT= 0.42; p<0.05). We identified a total of 3,013 SNPs through GBS, with 11 loci showing putative signs of being under selection. The variation based on 3,002 neutral loci evidenced low genetic structuration based on low FST values (p>0.05), indicating local panmixia. However, resampling algorithms pointed out that three samples from the external population were assigned (>98 %) in a cluster contrasting from the ones putatively under local panmixia - validating the newly applied genome-wide marker for studies on the population genetics at finer-scale resolution for T. brasiliensis. The presence of population structuring in some of the sampled points, as suggested by the mitochondrial marker, leads us to assume that infestations were probably initiated by small populations of females - demographic event poses a risk for rapid re-infestations. The local panmictic pattern revealed by the GBS marker poses a challenge for vector control measures, as re-infestation foci may be distributed over a wide geographical and ecological range. In such instances, vectors exhibit reduced susceptibility to conventional insecticide spraying operations since sylvatic populations are beyond the reach of these interventions. The pattern of infestation exhibited by T. brasiliensis necessitates integrating innovative strategies into the existing control framework, holding the potential to create a more resilient and adaptive vector control program. In our dataset, the results demonstrated that the genetic signals from both markers were complementary. Therefore, it is essential to consider the nature and inheritance pattern of each marker when inferring the pattern of re-infestations.

Correction: Urban vectors of Chagas disease in the American continent: A systematic review of epidemiological surveys

[This corrects the article DOI: 10.1371/journal.pntd.0011003.].

Marginal risk of domestic vector-borne Trypanosoma cruzi transmission after improved vector control of Triatoma infestans across a rural-to-urban gradient in the Argentine Chaco

The interruption of domestic vector-borne transmission of Trypanosoma cruzi in the Americas remains one of the main goals of the World Health Organization 2021-2030 road map for neglected tropical diseases. We implemented a longitudinal intervention program over 2015-2022 to suppress (peri)domestic Triatoma infestans in the municipality of Avia Terai, Chaco Province, Argentina and found that house infestation (3851 houses inspected) and triatomine abundance decreased over the first 2 years post-intervention (YPI), and remained stable thereafter associated to moderate pyrethroid resistant foci. Here we assessed selected components of transmission risk after interventions across the rural-to-urban gradient. We used multistage random sampling to select a municipality-wide sample of T. infestans. We examined 356 insects collected in 87 houses for T. cruzi infection using kDNA-PCR and identified their bloodmeal sources using an indirect ELISA. The overall prevalence of T. cruzi infection post-intervention was 1.7% (95% CI 0.7-3.6). Few houses (5.7%) (95% CI 2.5-12.8) harbored infected triatomines across the gradient. Infected triatomines were found in 5 peri-urban or rural dwellings over 1-4 years post-intervention. No infected insect was found in the urban area. The human blood index decreased from 66.2 at baseline to 42.8 at 1YPI and then increased to 92.9 at 4-5 YPI in the few infested domiciles detected. The percentage of houses with human-fed bugs displayed a similar temporal trend. Our results indicate marginal risks of domestic vector-borne transmission across the district after implementation of the intervention program. Ensuring sustainable vector surveillance coupled with human etiological diagnosis and treatment in hiperendemic areas like the Gran Chaco region, is urgently needed. 252 words.

Identifying Barriers and Facilitators for Home Reconstruction for Prevention of Chagas Disease: An Interview Study in Rural Loja Province, Ecuador

BACKGROUND

Chagas disease (CD) is a tropical parasitic disease spread by triatomine bugs, which are bugs that tend to infest precarious housing in rural and impoverished areas. Reducing exposure to the bugs, and thus the parasite they can carry, is essential to preventing CD in these areas. One promising long-term sustainable solution is to reconstruct precarious houses. Implementing home reconstruction requires an understanding of how householders construct barriers and facilitators they might encounter when considering whether to rebuild their homes.

METHODS

To understand barriers and facilitators to home reconstruction, we performed in-depth qualitative interviews with 33 residents of Canton Calvas, Loja, Ecuador, a high-risk endemic region. Thematic analysis was used to identify these barriers and facilitators.

RESULTS

The thematic analysis identified three facilitators (project facilitators, social facilitators, and economic facilitators) and two major barriers (low personal economy and extensive deterioration of existing homes).

CONCLUSIONS

The study findings provide important loci for assisting community members and for agents of change in home reconstruction projects to prevent CD. Specifically, the project and social facilitators suggest that collective community efforts (minga) are more likely to support home reconstruction intentions than individualist efforts, while the barriers suggest that addressing structural issues of economy and affordability are necessary.