Chagas Disease Ecology in the United States: Recent Advances in Understanding Trypanosoma cruzi Transmission Among Triatomines, Wildlife, and Domestic Animals and a Quantitative Synthesis of Vector-Host Interactions

Apparent absence of Trypanosoma cruzi in Mexican free-tailed bats (Tadarida brasiliensis) from Texas, USA

The Mexican free-tailed bat (Tadarida brasiliensis) is one of the most abundant mammals in North America. Mexican free-tailed bats have a wide geographic range stretching from northern South America to the western United States. Bats are theorized to be the original hosts for Trypanosoma cruzi -the causative agent of Chagas disease- and can serve as a source of infection to triatomine insect vectors that feed upon them. Chagas disease is a neglected tropical disease across the Americas where triatomines are present, including the southern United States, where Texas reports this highest number of locally-acquired human cases. To learn more about the role of bats in the ecology of Chagas disease in Texas, we surveyed a colony of Mexican free-tailed bats from Brazos County, Texas, for T. cruzi using carcasses salvaged after an extreme weather event. A total of 283 Mexican free-tailed bats collected in February 2021 were dissected and DNA from the hearts and kidneys was used for T. cruzi detection via qPCR. None of the bat hearts or kidneys tested positive for T. cruzi; this sample size affords 95% confidence that the true prevalence of T. cruzi in this population does not exceed 1%. Future sampling of multiple bat species as well as migrant and resident colonies of Mexican free-tailed bats across different times of the year over a broader geographic range would be useful in learning more about the role of bats in the ecology of Chagas disease in Texas.

Chagas Disease: A Silent Threat for Dogs and Humans

Chagas disease (CD) is a vector-borne Neglected Zoonotic Disease (NZD) caused by a flagellate protozoan, Trypanosoma cruzi, that affects various mammalian species across America, including humans and domestic animals. However, due to an increase in population movements and new routes of transmission, T. cruzi infection is presently considered a worldwide health concern, no longer restricted to endemic countries. Dogs play a major role in the domestic cycle by acting very efficiently as reservoirs and allowing the perpetuation of parasite transmission in endemic areas. Despite the significant progress made in recent years, still there is no vaccine against human and animal disease, there are few drugs available for the treatment of human CD, and there is no standard protocol for the treatment of canine CD. In this review, we highlight human and canine Chagas Disease in its different dimensions and interconnections. Dogs, which are considered to be the most important peridomestic reservoir and sentinel for the transmission of T. cruzi infection in a community, develop CD that is clinically similar to human CD. Therefore, an integrative approach, based on the One Health concept, bringing together the advances in genomics, immunology, and epidemiology can lead to the effective development of vaccines, new treatments, and innovative control strategies to tackle CD.

Abundant triatomines in Texas dog kennel environments: Triatomine collections, infection with Trypanosoma cruzi, and blood feeding hosts

Triatomine insects are vectors of the protozoan parasite Trypanosoma cruzi- the causative agent of Chagas disease. Chagas disease is endemic to Latin America and the southern United States and can cause severe cardiac damage in infected mammals, ranging from chronic disease to sudden death. Identifying interactions among triatomines, T. cruzi discrete typing units (DTUs), and blood feeding hosts is necessary to understand parasite transmission dynamics and effectively protect animal and human health. Through manual insect trapping efforts, kennel staff collections, and with the help of a trained scent detection dog, we collected triatomines from 10 multi-dog kennels across central and south Texas over a one-year period (2018-2019) and tested a subset to determine their T. cruzi infection status and identify the primary bloodmeal hosts. We collected 550 triatomines, including Triatoma gerstaeckeri (n = 515), Triatoma lecticularia (n = 15), Triatoma sanguisuga (n = 6), and Triatoma indictiva (n = 2), with an additional 10 nymphs and 2 adults unable to be identified to species. The trained dog collected 42 triatomines, including nymphs, from areas not previously considered vector habitat by the kennel owners. Using qPCR, we found a T. cruzi infection prevalence of 47 % (74/157), with T. lecticularia individuals more likely to be infected with T. cruzi than other species. Infected insects harbored two T. cruzi discrete typing units: TcI (64 %), TcIV (23 %), and mixed TcI/TcIV infections (13 %). Bloodmeal host identification was successful in 50/149 triatomines, revealing the majority (74 %) fed on a dog (Canis lupus), with other host species including humans (Homo sapiens), raccoons (Procyon lotor), chickens (Gallus gallus), wild pig (Sus scrofa), black vulture (Coragyps atratus), cat (Felis catus), and curve-billed thrasher (Toxostoma curviostre). Given the frequency of interactions between dogs and infected triatomines in these kennel environments, dogs may be an apt target for future vector control and T. cruzi intervention efforts.

RACCOONS (PROCYON LOTOR) SHOW HIGHER TRYPANOSOMA CRUZI DETECTION RATES THAN VIRGINIA OPOSSUMS (DIDELPHIS VIRGINIANA) IN SOUTH CAROLINA, USA

Chagas disease, a significant public health concern in the Americas, is caused by a protozoan parasite, Trypanosoma cruzi. The life cycle of T. cruzi involves kissing bugs (Triatoma spp.) functioning as vectors and mammalian species serving as hosts. Raccoons (Procyon lotor) and opossums (Didelphis virginiana) have been identified as important reservoir species in the life cycle of T. cruzi, but prevalence in both species in the southeastern US is currently understudied. We quantified T. cruzi prevalence in these two key reservoir species across our study area in South Carolina, US, and identified factors that may influence parasite detection. We collected whole blood from 183 raccoons and 126 opossums and used PCR to detect the presence of T. cruzi. We then used generalized linear models with parasite detection status as a binary response variable and predictor variables of land cover, distance to water, sex, season, and species. Our analysis indicated that raccoons experienced significantly higher parasite detection rates than Virginia opossums, with T. cruzi prevalence found to be 26.5% (95% confidence interval [CI], 20.0-33.8) in raccoons and 10.5% (95% CI, 5.51-17.5) in opossums. Overall, our results concur with previous studies, in that T. cruzi is established in reservoir host populations in natural areas of the southeastern US.

Host genetic backgrounds: the key to determining parasite-host adaptation

Parasitic diseases pose a significant threat to global public health, particularly in developing countries. Host genetic factors play a crucial role in determining susceptibility and resistance to infection. Recent advances in molecular and biological technologies have enabled significant breakthroughs in understanding the impact of host genes on parasite adaptation. In this comprehensive review, we analyze the host genetic factors that influence parasite adaptation, including hormones, nitric oxide, immune cells, cytokine gene polymorphisms, parasite-specific receptors, and metabolites. We also establish an interactive network to better illustrate the complex relationship between host genetic factors and parasite-host adaptation. Additionally, we discuss future directions and collaborative research priorities in the parasite-host adaptation field, including investigating the impact of host genes on the microbiome, developing more sophisticated models, identifying and characterizing parasite-specific receptors, utilizing patient-derived sera as diagnostic and therapeutic tools, and developing novel treatments and management strategies targeting specific host genetic factors. This review highlights the need for a comprehensive and systematic approach to investigating the underlying mechanisms of parasite-host adaptation, which requires interdisciplinary collaborations among biologists, geneticists, immunologists, and clinicians. By deepening our understanding of the complex interactions between host genetics and parasite adaptation, we can develop more effective and targeted interventions to prevent and treat parasitic diseases. Overall, this review provides a valuable resource for researchers and clinicians working in the parasitology field and offers insights into the future directions of this critical research area.

Trypanosoma cruzi infection in mammals in Florida: New insight into the transmission of T. cruzi in the southeastern United States

In Latin America, synanthropic mammalian reservoirs maintain Trypanosoma cruzi, a parasitic protozoan, where they facilitate the transmission of the parasite to humans and other reservoir hosts in peridomestic settings. In the United States, raccoons (Procyon lotor) and Virginia opossums (Didelphis virginiana) are known synanthropic T. cruzi reservoir hosts; however, the role these species have in the peridomestic transmission cycle in the US is not well understood. This study aimed to identify the suite of mammalian reservoirs of T. cruzi in Florida. We also compared infection prevalence in raccoon populations sampled from within and outside of the estimated distribution of the common T. cruzi vector in Florida to gain insight into how the arthropod vector distribution impacts the distribution of infected reservoirs in the state. Finally, to investigate the impact of peridomestic landscapes on parasite prevalence, we compared the prevalence of T. cruzi-infected raccoons and opossums across five paired peridomestic and sylvatic sites. We live-trapped and collected peripheral blood samples from 135 raccoons, 112 opossums, 18 nine-banded armadillos (Dasypus novemcinctus), and nine species of rodents in north central Florida. Using quantitative PCR methods, we found that raccoons (42.2%, 95% CI [34.2-50.7%]) and opossums (50.9%, 95% CI [41.8-60.0%]) were infected with T. cruzi and the prevalence across habitats was similar for both raccoons (peridomestic: n = 77, 44.2%, 95% CI [33.6-55.3%], sylvatic: n = 58, 39.7%, 95% CI [28.1-52.5%]) and opossums (peridomestic: n = 66, 48.5%, 95% CI [36.8-60.3%], sylvatic: n = 46, 54.3%, 95% CI [40.2-67.8%]). Raccoons sampled outside the estimated distribution of Triatoma sanguisuga were not infected with T. cruzi (n = 73, 0.0%, 95% CI [0.0-5.0%]). Our study did not indicate that peridomestic habitats in Florida maintained a higher infection prevalence than their sylvatic counterparts; however, we did find a difference in prevalence within vs. outside the estimated vector distribution in Florida.

Fluralaner systemic treatment of chickens results in mortality in Triatoma gerstaeckeri, vector of the agent of Chagas disease

BACKGROUND

Chagas disease remains a persistent vector-borne neglected tropical disease throughout the Americas and threatens both human and animal health. Diverse control methods have been used to target triatomine vector populations, with household insecticides being the most common. As an alternative to environmental sprays, host-targeted systemic insecticides (or endectocides) allow for application of chemicals to vertebrate hosts, resulting in toxic blood meals for arthropods (xenointoxication). In this study, we evaluated three systemic insecticide products for their ability to kill triatomines.

METHODS

Chickens were fed the insecticides orally, following which triatomines were allowed to feed on the treated chickens. The insecticide products tested included: Safe-Guard® Aquasol (fenbendazole), Ivomec® Pour-On (ivermectin) and Bravecto® (fluralaner). Triatoma gerstaeckeri nymphs were allowed to feed on insecticide-live birds at 0, 3, 7, 14, 28 and 56 days post-treatment. The survival and feeding status of the T. gerstaeckeri insects were recorded and analyzed using Kaplan-Meier curves and logistic regression.

RESULTS

Feeding on fluralaner-treated chickens resulted 50-100% mortality in T. gerstaeckeri over the first 14 days post-treatment but not later; in contrast, all insects that fed on fenbendazole- and ivermectin-treated chickens survived. Liquid chromatography tandem mass spectrometry (LC-QQQ) analysis, used to detect the concentration of fluralaner and fenbendazole in chicken plasma, revealed the presence of fluralaner in plasma at 3, 7, and 14 days post-treatment but not later, with the highest concentrations found at 3 and 7 days post-treatment. However, fenbendazole concentration was below the limit of detection at all time points.

CONCLUSIONS

Xenointoxication using fluralaner in poultry is a potential new tool for integrated vector control to reduce risk of Chagas disease.

Phenology and environmental predictors of Triatoma sanguisuga dispersal in east-central Texas, United States

Of 11 triatomine species in the United States (US), Triatoma sanguisuga has the widest distribution across a 23-state region encompassing the southeastern US. This species consistently feeds on humans and dogs and has a high infection prevalence with the Chagas parasite Trypanosoma cruzi, with over 30-60% of adults infected. Little is known about the phenology and environmental predictors of dispersal activity of Triatoma sanguisuga. Using manual searches standardized by effort, we sampled kissing bugs in east central Texas, US every other night from June to November 2020 to determine their phenology and environmental predictors of activity. We found 176 triatomines alive, all of which were T. sanguisuga, with peak collections in early August and cessation of activity by late October; the phenology as determined by this active surveillance matched what has been reported using a passive community science approach. Using a negative binomial regression, we found temperature to have a positive correlation with T. sanguisuga dispersal activity, while wind speed had a significant negative correlation. We identified increased collections during sampling sessions with precipitation during the preceding 22 h. Further, wind from the southwest - the direction of most of the sylvatic habitat in the study area - was correlated with an increased dispersal activity, suggesting wind-facilitated dispersal. Given concerns for human and animal Chagas disease within the distribution of T. sanguisuga, vector control strategies can be adapted based on the factors influencing dispersal behavior.

Effectiveness of fluralaner treatment regimens for the control of canine Chagas disease: A mathematical modeling study

BACKGROUND

Canine Chagas disease is caused by the protozoan parasite Trypanosoma cruzi and transmitted by insect triatomine vectors known as kissing bugs. The agent can cause cardiac damage and long-term heart disease and death in humans, dogs, and other mammals. In laboratory settings, treatment of dogs with systemic insecticides has been shown to be highly efficacious at killing triatomines that feed on treated dogs.

METHOD

We developed compartmental vector-host models of T. cruzi transmission between the triatomine and dog population accounting for the impact of seasonality and triatomine migration on disease transmission dynamics. We considered a single vector-host model without seasonality, and model with seasonality, and a spatially coupled model. We used the models to evaluate the effectiveness of the insecticide fluralaner with different durations of treatment regimens for reducing T. cruzi infection in different transmission settings.

RESULTS

In low and medium transmission settings, our model showed a marginal difference between the 3-month and 6-month regimens for reducing T. cruzi infection among dogs. The difference increases in the presence of seasonality and triatomine migration from a sylvatic transmission setting. In high transmission settings, the 3-month regimen was substantially more effective in reducing T. cruzi infections in dogs than the other regimens. Our model showed that increased migration rate reduces fluralaner effectiveness in all treatment regimens, but the relative reduction in effectiveness is minimal during the first years of treatment. However, if an additional 10% or more of triatomines killed by dog treatment were eaten by dogs, treatment could increase T. cruzi infections in the dog population at least during the first year of treatment.

CONCLUSION

Our analysis shows that treating all peridomestic dogs every three to six months for at least five years could be an effective measure to reduce T. cruzi infections in dogs and triatomines in peridomestic transmission settings. However, further studies at the local scale are needed to better understand the potential impact of routine use of fluralaner treatment on increasing dogs' consumption of dead triatomines.

The Trypanosoma cruzi TcrNT2 Nucleoside Transporter Is a Conduit for the Uptake of 5-F-2'-Deoxyuridine and Tubercidin Analogues

Among the scarce validated drug targets against Chagas disease (CD), caused by Trypanosoma cruzi, the parasite's nucleoside salvage system has recently attracted considerable attention. Although the trypanocidal activity of tubercidin (7-deazapurine) has long been known, the identification of a class of 7-substituted tubercidin analogs with potent in vitro and in vivo activity and much-enhanced selectivity has made nucleoside analogs among the most promising lead compounds against CD. Here, we investigate the recently identified TcrNT2 nucleoside transporter and its potential role in antimetabolite chemotherapy. TcrNT2, expressed in a Leishmania mexicana cell line lacking the NT1 nucleoside transporter locus, displayed very high selectivity and affinity for thymidine with a K_m of 0.26 ± 0.05 µM. The selectivity was explained by interactions of 2-oxo, 4-oxo, 5-Me, 3'-hydroxy and 5'-hydroxy with the transporter binding pocket, whereas a hydroxy group at the 2' position was deleterious to binding. This made 5-halogenated 2'-deoxyuridine analogues good substrates but 5-F-2'-deoxyuridine displayed disappointing activity against T. cruzi trypomastigotes. By comparing the EC₅₀ values of tubercidin and its 7-substituted analogues against L. mexicana Cas9, Cas9^ΔNT1 and Cas9^ΔNT1+TcrNT2 it was shown that TcrNT2 can take up tubercidin and, at a minimum, a subset of the analogs.

Prophylactic low-dose, bi-weekly benznidazole treatment fails to prevent Trypanosoma cruzi infection in dogs under intense transmission pressure

Trypanosoma cruzi naturally infects a wide variety of wild and domesticated mammals, in addition to humans. Depending on the infection dose and other factors, the acute infection can be life-threatening, and in all cases, the risk of chagasic heart disease is high in persistently infected hosts. Domestic, working, and semi-feral dogs in the Americas are at significant risk of T. cruzi infection and in certain settings in the southern United States, the risk of new infections can exceed 30% per year, even with the use of vector control protocols. In this study, we explored whether intermittent low-dose treatment with the trypanocidal compound benznidazole (BNZ) during the transmission season, could alter the number of new infections in dogs in an area of known, intense transmission pressure. Preliminary studies in mice suggested that twice-weekly administration of BNZ could prevent or truncate infections when parasites were delivered at the mid-point between BNZ doses. Pre-transmission season screening of 126 dogs identified 53 dogs (42.1%) as T. cruzi infection positive, based upon blood PCR and Luminex-based serology. Serial monitoring of the 67 uninfected dogs during the high transmission season (May to October) revealed 15 (22.4%) new infections, 6 in the untreated control group and 9 in the group receiving BNZ prophylaxis, indicating no impact of this prophylaxis regimen on the incidence of new infections. Although these studies suggest that rigorously timed and more potent dosing regimen may be needed to achieve an immediate benefit of prophylaxis, additional studies would be needed to determine if drug prophylaxis reduced disease severity despite this failure to prevent new infections.

Our Current Understanding of Chagas Disease and Trypanosoma cruzi Infection in the State of Florida — an Update on Research in this Region of the USA

Purpose of Review

Chagas disease (CD) is a neglected tropical disease caused by the protozoan parasite, Trypanosoma cruzi. Parasite transmission primarily occurs through direct interaction with an infected triatomine insect vector (kissing bug), but other routes are known. We aim to review the literature and discuss the unique circumstances of CD in the US state of Florida.

Recent Findings

Florida is home to naturally occurring kissing bugs that are invading homes and harbor T. cruzi. The state is also home to a diverse population of immigrants from Chagas-endemic regions in Latin America. In the USA, Florida is the state with the third highest estimated burden of CD, although the true prevalence is unknown.

Summary

Chagas disease is a chronic infection that often remains silent for decades. Those who manifest chronic disease may eventually die from debilitating cardiac and/or gastrointestinal manifestations. Florida is an opportune region of the USA for the study of CD, due to the existence of endemic transmission cycles in addition to the burden among people born in Chagas-endemic regions.

Toward New Epidemiological Landscapes of Trypanosoma cruzi (Kinetoplastida, Trypanosomatidae) Transmission under Future Human-Modified Land Cover and Climatic Change in Mexico

Chagas disease, caused by the protozoa Trypanosoma cruzi, is an important yet neglected disease that represents a severe public health problem in the Americas. Although the alteration of natural habitats and climate change can favor the establishment of new transmission cycles for T. cruzi, the compound effect of human-modified landscapes and current climate change on the transmission dynamics of T. cruzi has until now received little attention. A better understanding of the relationship between these factors and T. cruzi presence is an important step towards finding ways to mitigate the future impact of this disease on human communities. Here, we assess how wild and domestic cycles of T. cruzi transmission are related to human-modified landscapes and climate conditions (LUCC-CC). Using a Bayesian datamining framework, we measured the correlations among the presence of T. cruzi transmission cycles (sylvatic, rural, and urban) and historical land use, land cover, and climate for the period 1985 to 2012. We then estimated the potential range changes of T. cruzi transmission cycles under future land-use and -cover change and climate change scenarios for 2050 and 2070 time-horizons, with respect to “green” (RCP 2.6), “business-as-usual” (RCP 4.5), and “worst-case” (RCP 8.5) scenarios, and four general circulation models. Our results show how sylvatic and domestic transmission cycles could have historically interacted through the potential exchange of wild triatomines (insect vectors of T. cruzi) and mammals carrying T. cruzi, due to the proximity of human settlements (urban and rural) to natural habitats. However, T. cruzi transmission cycles in recent times (i.e., 2011) have undergone a domiciliation process where several triatomines have colonized and adapted to human dwellings and domestic species (e.g., dogs and cats) that can be the main blood sources for these triatomines. Accordingly, Chagas disease could become an emerging health problem in urban areas. Projecting potential future range shifts of T. cruzi transmission cycles under LUCC-CC scenarios we found for RCP 2.6 no expansion of favourable conditions for the presence of T. cruzi transmission cycles. However, for RCP 4.5 and 8.5, a significant range expansion of T. cruzi could be expected. We conclude that if sustainable goals are reached by appropriate changes in socio-economic and development policies we can expect no increase in suitable habitats for T. cruzi transmission cycles.

Characterization of triatomine bloodmeal sources using direct Sanger sequencing and amplicon deep sequencing methods

Knowledge of host associations of blood-feeding vectors may afford insights into managing disease systems and protecting public health. However, the ability of methods to distinguish bloodmeal sources varies widely. We used two methods—Sanger sequencing and amplicon deep sequencing—to target a 228 bp region of the vertebrate Cytochrome b gene and determine hosts fed upon by triatomines (n = 115) collected primarily in Texas, USA. Direct Sanger sequencing of PCR amplicons was successful for 36 samples (31%). Sanger sequencing revealed 15 distinct host species, which included humans, domestic animals (Canis lupus familiaris, Ovis aries, Gallus gallus, Bos taurus, Felis catus, and Capra hircus), wildlife (Rattus rattus, Incilius nebulifer, Sciurus carolinensis, Sciurus niger, and Odocoileus virginianus), and captive animals (Panthera tigris, Colobus spp., and Chelonoidis carbonaria). Samples sequenced by the Sanger method were also subjected to Illumina MiSeq amplicon deep sequencing. The amplicon deep sequencing results (average of 302,080 usable reads per sample) replicated the host community revealed using Sanger sequencing, and detected additional hosts in five triatomines (13.9%), including two additional blood sources (Procyon lotor and Bassariscus astutus). Up to four bloodmeal sources were detected in a single triatomine (I. nebulifer, Homo sapiens, C. lupus familiaris, and S. carolinensis). Enhanced understanding of vector-host-parasite networks may allow for integrated vector management programs focusing on highly-utilized and highly-infected host species.

Silver Nanoparticles Containing Fucoidan Synthesized by Green Method Have Anti-Trypanosoma cruzi Activity

The brown seaweed Spatoglossum schröederi synthesizes three bioactive fucoidans, the most abundant of which is fucan A. This fucoidan was extracted and its identity was confirmed by chemical analysis, Fourier-transform infrared spectroscopy (FTIR), and agarose gel electrophoresis. Thereafter, silver nanoparticles containing fucan A (AgFuc) were produced using an environmentally friendly synthesis method. AgFuc synthesis was analyzed via UV-vis spectroscopy and FTIR, which confirmed the presence of both silver and fucan A in the AgFuc product. Dynamic light scattering (DLS), X-ray diffraction, scanning electron microscopy, and atomic force microscopy revealed that the AgFuc particles were ~180.0 nm in size and spherical in shape. DLS further demonstrated that AgFuc was stable for five months. Coupled plasma optical emission spectrometry showed that the AgFuc particles contained 5% silver and 95% sugar. AgFuc was shown to be more effective in inhibiting the ability of parasites to reduce MTT than fucan A or silver, regardless of treatment time. In addition, AgFuc induced the death of ~60% of parasites by necrosis and ~17% by apoptosis. Therefore, AgFuc induces damage to the parasites' mitochondria, which suggests that it is an anti-Trypanosoma cruzi agent. This is the first study to analyze silver nanoparticles containing fucan as an anti-Trypanosoma cruzi agent. Our data indicate that AgFuc nanoparticles have potential therapeutic applications, which should be determined via preclinical in vitro and in vivo studies.