Population genomics and geographic dispersal in Chagas disease vectors: Landscape drivers and evidence of possible adaptation to the domestic setting.

Accurate prediction of vectors dispersal, as well as identification of adaptations that allow blood-feeding vectors to thrive in built environments, are a basis for effective disease control. Here we adopted a landscape genomics approach to assay gene flow, possible local adaptation, and drivers of population structure in Rhodnius ecuadoriensis, an important vector of Chagas disease. We used a reduced-representation sequencing technique (2b-RADseq) to obtain 2,552 SNP markers across 272 R. ecuadoriensis samples from 25 collection sites in southern Ecuador. Evidence of high and directional gene flow between seven wild and domestic population pairs across our study site indicates insecticide-based control will be hindered by repeated re-infestation of houses from the forest. Preliminary genome scans across multiple population pairs revealed shared outlier loci potentially consistent with local adaptation to the domestic setting, which we mapped to genes involved with embryogenesis and saliva production. Landscape genomic models showed elevation is a key barrier to R. ecuadoriensis dispersal. Together our results shed early light on the genomic adaptation in triatomine vectors and facilitate vector control by predicting that spatially-targeted, proactive interventions would be more efficacious than current, reactive approaches.

Prevalence, infected density or individual probability of infection? Assessing vector infection risk in the wild transmission of Chagas disease.

Vector-borne infectious disease dynamics result mainly from the intertwined effect of the diversity, abundance, and behaviour of hosts and vectors. Most studies, however, have analysed the relationship between host-species diversity and infection risk, focusing on vector population instead of individuals, probably dismissing the level at which the transmission process occurs. In this paper, we examine the importance of the host community in accounting for infection risk, at both population and individual levels, using the wild transmission of the protozoan that causes Chagas disease as a vector-borne disease model. Chagas disease is caused by Trypanosoma cruzi, transmitted by triatomine insects to mammals. We assessed if T. cruzi infection in vectors is explained by small mammal diversity and their densities (total and infected), when infection risk is measured at population level as infection prevalence (under a frequency-dependent transmission approach) and as density of infected vectors (density-dependent transmission approach), and when measured at individual level as vector infection probability. We analysed the infection status of 1974 vectors and co-occurring small mammal hosts in a semiarid-Mediterranean ecosystem. Results revealed that regardless of the level of analysis, only one host rodent species accounted for most variation in vector infection risk, suggesting a key role in the transmission cycle. To determine the factors explaining vector-borne disease dynamics, infection risk should be assessed at different scales, reflecting the factors meaningful from the vector's perspective and considering vector class-specific features.

Organs infected with Trypanosoma cruzi and DTU identification in the naturally infected rodent Octodon degus.

Chagas disease is a public health problem in America. Its parasite, Trypanosoma cruzi, presents different discrete typing units (DTUs), colonizes organs of mammalian hosts in chronic infections, and presents tropism for particular organs in experimental infections. We evaluated T. cruzi tropism towards organs on the naturally infected rodent Octodon degus, identifying the parasites' DTUs, by means of conventional PCR and hybridization. Almost all the analyzed organs presented T. cruzi. More than 42% of the tested oesophagus, skin, skeletal muscle, brain and intestine showed T. cruzi DNA. Other nine types of organs were infected in over 15%. These results suggest that there is some tropism by T. cruzi in chronically infected O. degus. DTU TcV was present in 92.5% of infected organs with identified DTUs; this DTU is frequently reported in human infections in the Southern Cone of South America. Few organs showed mixed DTU infections. This is one of the few reports on the outcome of chronic natural T. cruzi-infection in wild mammal hosts exposed to naturally infected vectors.

Global spatial assessment of Aedes aegypti and Culex quinquefasciatus: a scenario of Zika virus exposure.

Zika virus (ZIKV) is an arbovirus transmitted mainly by Aedes aegypti mosquitoes. Recent scientific evidence on Culex quinquefasciatus has suggested its potential as a vector for ZIKV, which may change the current risk zones. We aimed to quantify the world population potentially exposed to ZIKV in a spatially explicit way, considering the primary vector (A. aegypti) and the potential vector (C. quinquefasciatus). Our model combined species distribution modelling of mosquito species with spatially explicit human population data to estimate ZIKV exposure risk. We estimated the potential global distribution of C. quinquefasciatus and estimated its potential interaction zones with A. aegypti. Then we evaluated the risk zones for ZIKV considering both vectors. Finally, we quantified and compared the people under risk associated with each vector by risk level, country and continent. We found that C. quinquefasciatus had a more temperate distribution until 42° in both hemispheres, while the risk involving A. aegypti is concentrated mainly in tropical latitudes until 35° in both hemispheres. Globally, 4.2 billion people are under risk associated with ZIKV. Around 2.6 billon people are under very high risk associated with C. quinquefasciatus and 1 billion people associated with A. aegypti. Several countries could be exposed to ZIKV, which emphasises the need to clarify the competence of C. quinquefasciatus as a potential vector as soon as possible. The models presented here represent a tool for risk management, public health planning, mosquito control and preventive actions, especially to focus efforts on the most affected areas.

Spatial distribution of an infectious disease in a small mammal community.

Chagas disease is a zoonosis caused by the parasite Trypanosoma cruzi and transmitted by insect vectors to several mammals, but little is known about its spatial epidemiology. We assessed the spatial distribution of T. cruzi infection in vectors and small mammals to test if mammal infection status is related to the proximity to vector colonies. During four consecutive years we captured and georeferenced the locations of mammal species and colonies of Mepraia spinolai, a restricted-movement vector. Infection status on mammals and vectors was evaluated by molecular techniques. To examine the effect of vector colonies on mammal infection status, we constructed an infection distance index using the distance between the location of each captured mammal to each vector colony and the average T. cruzi prevalence of each vector colony, weighted by the number of colonies assessed. We collected and evaluated T. cruzi infection in 944 mammals and 1976 M. spinolai. We found a significant effect of the infection distance index in explaining their infection status, when considering all mammal species together. By examining the most abundant species separately, we found this effect only for the diurnal and gregarious rodent Octodon degus. Spatially explicit models involving the prevalence and location of infected vectors and hosts had not been reported previously for a wild disease.

Modeling the spatial distribution of Chagas disease vectors using environmental variables and people´s knowledge.

BACKGROUND: Chagas disease is caused by the protozoan Trypanosoma cruzi, which is transmitted to mammal hosts by triatomine insect vectors. The goal of this study was to model the spatial distribution of triatomine species in an endemic area. METHODS: Vector's locations were obtained with a rural householders' survey. This information was combined with environmental data obtained from remote sensors, land use maps and topographic SRTM data, using the machine learning algorithm Random Forests to model species distribution. We analysed the combination of variables on three scales: 10 km, 5 km and 2.5 km cell size grids. RESULTS: The best estimation, explaining 46.2% of the triatomines spatial distribution, was obtained for 5 km of spatial resolution. Presence probability distribution increases from central Chile towards the north, tending to cover the central-coastal region and avoiding areas of the Andes range. CONCLUSIONS: The methodology presented here was useful to model the distribution of triatomines in an endemic area; it is best explained using 5 km of spatial resolution, and their presence increases in the northern part of the study area. This study's methodology can be replicated in other countries with Chagas disease or other vectorial transmitted diseases, and be used to locate high risk areas and to optimize resource allocation, for prevention and control of vectorial diseases.

Diet of the sylvatic triatomine Mepraia spinolai: Association with Trypanosoma cruzi infection near human settlements.

The proximity between infectious disease vector populations and human settlements, and the infection prevalence of vector populations can determine the rate of encounters between vectors and humans and hence infection risk. The diet of sylvatic triatomine vectors (kissing bugs) provides evidence about the host species involved in the maintenance of the protozoan Trypanosoma cruzi, the etiological agent of Chagas disease. Here, we characterized the diet of the Chilean endemic triatomine Mepraia spinolai using Next Generation Sequencing (NGS), and evaluated the relation between T. cruzi infection status and proximity to human settlements, with the proportion of human and human-associated (domestic and synanthropic) vertebrates in the diet. We sampled 28 M. spinolai populations, covering a latitudinal range of ∼800 km in Chile. For each population, genomic DNA was obtained from M. spinolai intestinal content. We assessed T. cruzi infection individually, and sequenced vertebrate cytochrome b to characterize the diet from infected and uninfected pooled samples. Human and human-associated animals were present in the diet of both T. cruzi-infected (13.50 %) and uninfected (10.43 %) kissing bugs. The proportion of human and human-associated vertebrates in the diet of infected M. spinolai was negatively associated with the distance from surrounding human settlements, but no relationship was detected for uninfected kissing bugs. This pattern could be related to alterations of kissing bug feeding behavior when infected by the protozoan. Our results highlight the relevance of developing a deeper knowledge of the wild transmission cycle of T. cruzi, thus advancing in the surveillance of vectors present in the natural environment near human settlements.

Opportunistic or selective? Stage-dependent feeding behavior in a wild vector of Chagas disease.

The composition and contribution of different host species in the dynamics of vector-borne zoonotic parasites are particularly relevant for public health. Hence, the study of host selection by vectors is fundamental. Developmental stage and infection status are factors that may modulate vector feeding behavior. In the semi-arid Mediterranean ecosystem of South America, the transmission of Trypanosoma cruzi, the protozoan causing Chagas disease, includes the triatomine vector Mepraia spinolai and several vertebrate species. In this field study, we examined whether M. spinolai exhibits an opportunistic feeding behavior dependent upon developmental stage and/or infection status. We found that M. spinolai does not feed according to the relative availability of vertebrate species. In addition, early stage nymphs (first/second instars) fed on twice as many different species as middle (third/fourth instars) and late (fifth instars and adults) M. spinolai, with the former feeding on native rodents and lizards and the latter mostly on rabbits. Infected and uninfected M. spinolai showed similar feeding profiles. Wild triatomine species might be described as stage-dependent selective blood feeders, as a consequence of the temporal and spatial scale at which host-vector interactions occur, highlighting that all developmental stages might be infected and capable of transmitting T. cruzi.

Humans as blood-feeding sources in sylvatic triatomines of Chile unveiled by next-generation sequencing.

BACKGROUND: Triatomines are blood-sucking insects capable of transmitting Trypanosoma cruzi, the parasite that causes Chagas disease in humans. Vectorial transmission entails an infected triatomine feeding on a vertebrate host, release of triatomine infective dejections, and host infection by the entry of parasites through mucous membranes, skin abrasions, or the biting site; therefore, transmission to humans is related to the triatomine-human contact. In this cross-sectional study, we evaluated whether humans were detected in the diet of three sylvatic triatomine species (Mepraia parapatrica, Mepraia spinolai, and Triatoma infestans) present in the semiarid-Mediterranean ecosystem of Chile. METHODS: We used triatomines collected from 32 sites across 1100 km, with an overall T. cruzi infection frequency of 47.1% (N = 4287 total specimens) by conventional PCR or qPCR. First, we amplified the vertebrate cytochrome b gene (cytb) from all DNA samples obtained from triatomine intestinal contents. Then, we sequenced cytb-positive PCR products in pools of 10-20 triatomines each, grouped by site. The filtered sequences were grouped into amplicon sequence variants (ASVs) with a minimum abundance of 100 reads. ASVs were identified by selecting the best BLASTn match against the NCBI nucleotide database. RESULTS: Overall, 16 mammal (including human), 14 bird, and seven reptile species were identified in the diet of sylvatic triatomines. Humans were part of the diet of all analyzed triatomine species, and it was detected in 19 sites representing 12.19% of the sequences. CONCLUSIONS: Sylvatic triatomine species from Chile feed on a variety of vertebrate species; many of them are detected here for the first time in their diet. Our results highlight that the sylvatic triatomine-human contact is noteworthy. Education must be enforced for local inhabitants, workers, and tourists arriving in endemic areas to avoid or minimize the risk of exposure to Chagas disease vectors.

Molecular surveillance of potential SARS-CoV-2 reservoir hosts in wildlife rehabilitation centers.

BACKGROUND: The COVID-19 pandemic, caused by SARS-CoV-2 infection, has become the most devastating zoonotic event in recent times, with negative impacts on both human and animal welfare as well as on the global economy. Although SARS-CoV-2 is considered a human virus, it likely emerged from animals, and it can infect both domestic and wild animals. This constitutes a risk for human and animal health including wildlife with evidence of SARS-CoV-2 horizontal transmission back and forth between humans and wild animals. AIM: Molecular surveillance in different wildlife rehabilitation centers and wildlife associated institutions in Chile, which are critical points of animal-human interaction and wildlife conservation, especially since the aim of wildlife rehabilitation centers is to reintroduce animals to their original habitat. MATERIALS AND METHODS: The survey was conducted in six WRCs and three wildlife associated institutions. A total of 185 samples were obtained from 83 individuals belonging to 15 different species, including vulnerable and endangered species. Each specimen was sampled with two different swabs: one oropharyngeal or nasopharyngeal according to the nostril diameter, and/or a second rectal sample. RNA was extracted from the samples and two different molecular assays were performed: first, a conventional RT-PCR with pan-coronavirus primers and a second SARS-CoV-2 qPCR targeting the N and S genes. RESULTS: All 185 samples were negative for SARS-CoV-2. CLINICAL RELEVANCE: This study constitutes the first report on the surveillance of SARS-CoV-2 from wildlife treated in rehabilitation centers in Chile, and supports the biosafety procedures adopted in those centers.

Trypanosoma cruzi Parasite Load Modulates the Circadian Activity Pattern of Triatoma infestans.

American trypanosomiasis is a disease caused by the flagellate protozoan Trypanosoma cruzi, which is transmitted mainly in endemic areas by blood-sucking triatomine vectors. Triatoma infestans is the most important vector in the southern cone of South America, exhibiting a nocturnal host-seeking behavior. It has been previously documented that the parasite produces changes in some triatomine species, but this is the first time that the behavior of a vector has been evaluated in relation to its parasite load. After comparing the movement events and distance traveled of infected and non-infected T. infestans, we evaluated the change produced by different T. cruzi parasite loads on its circadian locomotor activity. We observed differences between infected and non-infected triatomines, and a significant relation between the parasite load and the increase in locomotor activity of T. infestans, which was accentuated during the photophase. This could have direct implications on the transmission of T. cruzi, as the increased movement and distance traveled could enhance the contact of the vector with the host, while increasing the predation risk for the vector, which could both constitute a risk for vectorial and oral transmission to mammals.

The Parasite Load of Trypanosoma cruzi Modulates Feeding and Defecation Patterns of the Chagas Disease Vector Triatoma infestans.

Trypanosoma cruzi is the causal agent of Chagas disease, a parasitic zoonosis transmitted mainly through the feces of triatomine insects. Triatoma infestans is the main triatomine vector of this disease in South America. Previous research has shown that T. cruzi infection modifies the behavior of triatomines. We evaluated, for the first time, the effect of parasite load on feeding and defecation behavior, which we quantified by using real-time PCR. The detection time of the host was shorter in infected individuals, and the number of bites increased, while the dejection time was reduced when compared with the non-infected group. A significant correlation between the parasite load and the behavioral changes registered in the infected triatomines was found. These results would indicate that the intensity of T. cruzi infection modulates the feeding and defecation behavior of T. infestans, increasing the vector competence of this triatomine vector.

Trypanosoma cruzi infection in the wild Chagas disease vector, Mepraia spinolai: Parasitic load, discrete typing units, and blood meal sources.

BACKGROUND: Mepraia spinolai, a wild vector of Trypanosoma cruzi in Chile, is an abundant triatomine species that is frequently infected by the parasite that causes Chagas disease. The aim of this study was to determine if the parasitic load of T. cruzi in M. spinolai is related to its blood meal source and the infecting DTUs of T. cruzi. METHODS: The vector was captured in rural areas. In the laboratory, DNA was extracted from its abdomen and T. cruzi was quantified using qPCR. Real time PCR assays for four T. cruzi DTUs were performed. Blood meal sources were identified by real-time PCR amplification of vertebrate cytochrome b gene sequences coupled with high resolution melting (HRM). RESULTS: Trypanosoma cruzi was detected in 735 M. spinolai; in 484 we identified one blood meal source, corresponding to human, sylvatic, and domestic species. From these, in 224 we were able to discriminate the infecting DTU. When comparing the parasitic loads between the unique blood meal sources, no significant differences were found, but infections with more than one DTU showed higher parasitic loads than single infections. DTU TcI was detected in a high proportion of the samples. CONCLUSIONS: Higher parasitic loads are related to a greater number of T. cruzi DTUs infecting M. spinolai, and this triatomine seems to have a wide span of vertebrate species in its diet.

Trypanosoma cruzi DNA in Desmodus rotundus (common vampire bat) and Histiotus montanus (small big-eared brown bat) from Chile.

The protozoan Trypanosoma cruzi, the causative agent of Chagas disease, is transmitted by infected feces or consumption of blood-sucking triatomine insects to several mammalian orders including Chiroptera. In Chile, the distribution of several insectivorous and one hematophagous bat species overlaps with those of triatomine vectors, but the T. cruzi infection status of local chiropterans is unknown. In 2018, we live-captured bats from two protected areas in Chile to collect plagiopatagium tissue, feces and perianal swab samples, in search for T. cruzi-DNA by real time PCR assays using species-specific primers. In Pan de Azúcar island (∼26°S), we examined a roost of Desmodus rotundus (common vampire bat) and sampled tissue from 17 individuals, detecting T. cruzi-DNA in five of them. In Las Chinchillas National Reserve (∼31°S), we examined two roosts of Histiotus montanus (small big-eared brown bat), collecting feces or perianal swab samples from eight individuals, detecting T. cruzi-DNA in four of them. This is the first report of T. cruzi-DNA evidence in bat species from Chile. Both vector-borne and oral transmission are potential infection routes that can explain our results. Further investigation is needed for a better understanding of the role of bats in the T. cruzi transmission cycle.

Sylvatic foci of the Chagas disease vector Triatoma infestans in Chile: description of a new focus and challenges for control programs.

Triatoma infestans is one of the main domestic vectors of Chagas disease. Reports of wild habitat occurrences have recently increased. In Chile, after a successful elimination campaign of T. infestans domestic infestation, a sylvatic focus was reported in bromeliads in the metropolitan region. Here, we report a new focus of sylvatic T. infestans inhabiting rock piles in the Valparaíso region in central Chile. All T. infestans captured were nymphal instars living among the stones, which were inhabited by several mammal species, along with the sylvatic triatomine vector Mepraia spinolai. We found a prevalence of infection with Trypanosoma cruzi of 36.54% in T. infestans, similar to the previous report for sylvatic specimens from bromeliads. Sylvatic populations of T. infestans should be studied at different geographic scales to elucidate their role in the maintenance of the sylvatic transmission cycle of T. cruzi and their possible role in threatening the domestic elimination of this vector. This information should be used to re-design the control programs in Chile to avoid the re-establishment of the domestic cycle.

Trypanosomatid Infections among Vertebrates of Chile: A Systematic Review.

We present a review on the natural infection by trypanosomatids of nonhuman vertebrates in Chile, aiming to synthesize and update the knowledge on the diversity of trypanosomatids infecting native and alien vertebrate species. To this end, we conducted a systematic review of literature records published from 1900 to April 2020 on four databases, focusing on the 21 genera of trypanosomatids and Chile. The methods and findings of our review have been based on the preferred reporting items for systematic reviews and meta-analysis (prisma) checklist. We found 29,756 records but only 71 presented relevant information for this review. Overall, there are only two reported trypanosomatid genera infecting vertebrate species in Chile, the genera Trypanosoma and Leishmania. The former is mostly represented by Trypanosoma cruzi (90% of the total records) and to a much lesser extent by Trypanosoma avium, Trypanosoma humboldti, Trypanosoma lewisi, and a couple of unidentified trypanosomatids. A total of 25 mammals have been reported as being infected by T. cruzi, including 14 native and 11 alien species from Orders Artiodactyla, Carnivora, Chiroptera, Didelphimorphia, Lagomorpha, Perissodactyla, and Rodentia. Extensive screening studies using new analytical tools are necessary to grasp the whole potential diversity of trypanosomatid species infecting vertebrates in Chile.

Trypanosoma cruzi could affect wild triatomine approaching behaviour to humans by altering vector nutritional status: A field test.

Hematophagous insects exhibit complex behaviour when searching for blood-meals, responding to several host stimuli. The hematophagous insect Mepraia spinolai is a wild vector of Trypanosoma cruzi, causative agent of Chagas disease in humans, in the semiarid-Mediterranean ecosystem of Chile. In this study, we evaluated the association between the approaching behaviour to a human host, with T. cruzi infection status and nutritional condition of M. spinolai. To this end, we captured 501 individuals in six consecutive 10 min-timespan, using a human as bait. Captured vectors were weighed, photographed and measured to calculate their nutritional status by means of a Standardized Body Mass Index. Trypanosoma cruzi infection was assessed in the intestinal content by using a real-time PCR assay. Ordinal logistic regressions were performed separately for infected and uninfected groups to evaluate if the nutritional status was associated with the approaching behaviour to a human host, recorded as the time-span of capture. Nutritional status of uninfected triatomines was higher than that from infected ones (p < 0.005). Among the infected, those with higher nutritional status approached first (p < 0.01); there was no effect of nutritional status in the uninfected group. Trypanosoma cruzi infection might affect the foraging behaviour of M. spinolai under natural conditions, probably deteriorating nutritional status and/or altering vector detection abilities.

Potential impact of climate change on the geographical distribution of two wild vectors of Chagas disease in Chile: Mepraia spinolai and Mepraia gajardoi.

BACKGROUND: Mepraia gajardoi and Mepraia spinolai are endemic triatomine vector species of Trypanosoma cruzi, a parasite that causes Chagas disease. These vectors inhabit arid, semiarid and Mediterranean areas of Chile. Mepraia gajardoi occurs from 18° to 25°S, and M. spinolai from 26° to 34°S. Even though both species are involved in T. cruzi transmission in the Pacific side of the Southern Cone of South America, no study has modelled their distributions at a regional scale. Therefore, the aim of this study is to estimate the potential geographical distribution of M. spinolai and M. gajardoi under current and future climate scenarios. METHODS: We used the Maxent algorithm to model the ecological niche of M. spinolai and M. gajardoi, estimating their potential distributions from current climate information and projecting their distributions to future climatic conditions under representative concentration pathways (RCP) 2.6, 4.5, 6.0 and 8.5 scenarios. Future predictions of suitability were constructed considering both higher and lower public health risk situations. RESULTS: The current potential distributions of both species were broader than their known ranges. For both species, climate change projections for 2070 in RCP 2.6, 4.5, 6.0 and 8.5 scenarios showed different results depending on the methodology used. The higher risk situation showed new suitable areas, but the lower risk situation modelled a net reduction in the future potential distribution areas of M. spinolai and M. gajardoi. CONCLUSIONS: The suitable areas for both species may be greater than currently known, generating new challenges in terms of vector control and prevention. Under future climate conditions, these species could modify their potential geographical range. Preventive measures to avoid accidental human vectorial transmission by wild vectors of T. cruzi become critical considering the uncertainty of future suitable areas projected in this study.

Spatio-temporal characterization of Trypanosoma cruzi infection and discrete typing units infecting hosts and vectors from non-domestic foci of Chile.

BACKGROUND: Trypanosoma cruzi is a protozoan parasite that is transmitted by triatomine vectors to mammals. It is classified in six discrete typing units (DTUs). In Chile, domestic vectorial transmission has been interrupted; however, the parasite is maintained in non-domestic foci. The aim of this study was to describe T. cruzi infection and DTU composition in mammals and triatomines from several non-domestic populations of North-Central Chile and to evaluate their spatio-temporal variations. METHODOLOGY/PRINCIPAL FINDINGS: A total of 710 small mammals and 1140 triatomines captured in six localities during two study periods (summer/winter) of the same year were analyzed by conventional PCR to detect kDNA of T. cruzi. Positive samples were DNA blotted and hybridized with specific probes for detection of DTUs TcI, TcII, TcV, and TcVI. Infection status was modeled, and cluster analysis was performed in each locality. We detected 30.1% of overall infection in small mammals and 34.1% in triatomines, with higher rates in synanthropic mammals and in M. spinolai. We identified infecting DTUs in 45 mammals and 110 triatomines, present more commonly as single infections; the most frequent DTU detected was TcI. Differences in infection rates among species, localities and study periods were detected in small mammals, and between triatomine species; temporally, infection presented opposite patterns between mammals and triatomines. Infection clustering was frequent in vectors, and one locality exhibited half of the 21 clusters found. CONCLUSIONS/SIGNIFICANCE: We determined T. cruzi infection in natural host and vector populations simultaneously in a spatially widespread manner during two study periods. All captured species presented T. cruzi infection, showing spatial and temporal variations. Trypanosoma cruzi distribution can be clustered in space and time. These clusters may represent different spatial and temporal risks of transmission.

Trypanosoma cruzi load in synanthropic rodents from rural areas in Chile.

BACKGROUND: Trypanosoma cruzi is the agent of Chagas disease, a major public health problem in Latin America. Many wild and domestic animals are naturally infected with T. cruzi; rodents are one of the groups which have been consistently detected infected in different countries. The aim of this work was to characterize blood T. cruzi load in naturally infected rodents from a Chagas disease endemic region in Chile. METHODS: Baited traps were set in domestic and peridomestic areas of rural dwellings. The rodents were anesthetized and blood sampled; DNA was extracted and the parasite load was quantified by T. cruzi satellite DNA real-time PCR assays. RESULTS: Seventy-one rodents of four species, Rattus rattus, Mus musculus, Phyllotis darwini and Octodon degus, were captured; R. rattus was the most abundant species. Fifty-nine samples (83.1%) were T. cruzi-positive and the median value of the parasite load was 2.99 parasite equivalents (par-eq)/ml. The comparison of frequency of infection or parasite load by species showed no differences. However, one R. rattus presented very elevated parasitemia (1644 par-eq/ml). CONCLUSIONS: The overall levels of parasitemia were similar to those found in humans in Chile. The high infection levels in exotic and endemic rodents very near to rural settlements increases their relevance as T. cruzi hosts.