Ecology, evolution and control of Chagas disease: a century of neglected modelling and a promising future

Effectiveness of Systemic Insecticide Dog Treatment for the Control of Chagas Disease in the Tropics

Chagas disease, caused by Trypanosoma cruzi and transmitted by triatomines, can lead to severe cardiac issues and mortality in many mammals. Recent studies have shown that systemic insecticide treatment of dogs is highly effective in killing triatomines. Here, we assessed the impact of dog treatment on T. cruzi transmission. We developed a mathematical model of T. cruzi transmission among triatomines, dogs, humans, and rodents. We used the model to evaluate the impact of dog treatment regimens on T. cruzi transmission dynamics to determine their effectiveness in reducing T. cruzi infection among hosts. We show that a 3-month treatment regimen may reduce T. cruzi incidence among humans by 59-80% in a high transmission setting, and 26-82% in a low transmission setting. An annual treatment may reduce incidence among humans by 49-74% in a high transmission setting, and by 11-76% in a low transmission setting. However, dog treatment may substantially increase T. cruzi prevalence among dogs if dog consumption of dead triatomines increases. Our model indicates that dog treatment may reduce T. cruzi infections among humans, but it may increase infections in dogs. Therefore, a holistic approach targeting different hosts is necessary for Chagas elimination.

Distribution of Triatoma dimidiata sensu lato (Reduviidae: Triatominae) and Risk Factors Associated with Household Invasion in Northern Belize, Central America

To date, Triatoma dimidiata sensu lato [Reduviidae: Triatominae (Latreille 1811)] remains the sole vector species associated with Chagas disease transmission reported from Belize. Human infection data are limited for Belize and the disease transmission dynamics have not been thoroughly investigated, yet the likelihood of autochthonous transmission is supported by the widespread collection of infected vectors from within local households. Here, we report updated infection rates of the vector population and infestation rates for villages in north and central Belize. Overall, 275 households were enrolled in an ongoing vector surveillance program. Of the 41 insects collected, 25 were PCR positive for T. cruzi, indicating an infection rate as high as 60%. To further characterize the epidemiological risk of human-vector contact, determinants of household invasion were modeled. Local households were surveyed and characterized with respect to over 25 key factors that may be associated with household infestation by T. dimidiata s.l. While final models were not strongly predictive with respect to the risk factors that were surveyed, likely due to the low number of collection observations, the presence of domestic/peri-domestic dogs, nearby light sources, and household structure materials could be the focus of continued risk assessments. In northern Belize, this vector survey lends support to T. dimidiata s.l. inhabiting sylvatic settings as opposed to the classical paradigm of domiciliated vector populations. This designation has strong implications for the local level of human exposure risk which can help guide vector surveillance and control resources.

Spatiotemporal variations in exposure: Chagas disease in Colombia as a case study

Age-stratified serosurvey data are often used to understand spatiotemporal trends in disease incidence and exposure through estimating the Force-of-Infection (FoI). Typically, median or mean FoI estimates are used as the response variable in predictive models, often overlooking the uncertainty in estimated FoI values when fitting models and evaluating their predictive ability. To assess how this uncertainty impact predictions, we compared three approaches with three levels of uncertainty integration. We propose a performance indicator to assess how predictions reflect initial uncertainty.

In Colombia, 76 serosurveys (1980–2014) conducted at municipality level provided age-stratified Chagas disease prevalence data. The yearly FoI was estimated at the serosurvey level using a time-varying catalytic model. Environmental, demographic and entomological predictors were used to fit and predict the FoI at municipality level from 1980 to 2010 across Colombia.

A stratified bootstrap method was used to fit the models without temporal autocorrelation at the serosurvey level. The predictive ability of each model was evaluated to select the best-fit models within urban, rural and (Amerindian) indigenous settings. Model averaging, with the 10 best-fit models identified, was used to generate predictions.

Our analysis shows a risk of overconfidence in model predictions when median estimates of FoI alone are used to fit and evaluate models, failing to account for uncertainty in FoI estimates. Our proposed methodology fully propagates uncertainty in the estimated FoI onto the generated predictions, providing realistic assessments of both central tendency and current uncertainty surrounding exposure to Chagas disease.

A voluntary use of insecticide treated nets can stop the vector transmission of Chagas disease

One of the stated goals of the London Declaration on Neglected Tropical Diseases is the interruption of domiciliary transmissions of Chagas disease in the region of the Americas. We used a game-theoretic approach to assess the voluntary use of insecticide treated nets (ITNs) in the prevention of the spread of infection through vector bites. Our results show that individuals behave rationally and weigh the risks of insect bites against the cost of the ITNs. The optimal voluntary use of ITNs results in predicted incidence rates that closely track the real incidence rates in Latin America. This means that ITNs are effective and could be used to control the spread of the disease by relying on individual decisions rather than centralized policies. Our model shows that to completely eradicate the vector transmission through the voluntary individual use of ITNs, the cost of ITNs should be as low as possible.

Human Trypanosoma cruzi infection is driven by eco-social interactions in rural communities of the Argentine Chaco

The transmission of Trypanosoma cruzi to humans is determined by multiple ecological, socio-economic and cultural factors acting at different scales. Their effects on human infection with T. cruzi have often been examined separately or using a limited set of ecological and socio-demographic variables. Herein, we integrated the ecological and social dimensions of human infection risk with the spatial distribution patterns of human and vector (Triatoma infestans) infection in rural communities of the Argentine Chaco composed of indigenous people (90% Qom) and a creole minority. We conducted serosurveys in 470 households aiming at complete population enumeration over 2012–2015. The estimated seroprevalence of T. cruzi prior to the implementation of an insecticide spraying campaign (2008) was 29.0% (N = 1,373 in 301 households), and was twice as large in Qom than creoles. Using generalized linear mixed models, human seropositive cases significantly increased with infected triatomine abundance, having a seropositive household co-inhabitant and household social vulnerability (a multidimensional index of poverty), and significantly decreased with increasing host availability in sleeping quarters (an index summarizing the number of domestic hosts for T. infestans). Vulnerable household residents were exposed to a higher risk of infection even at low infected-vector abundances. The risk of being seropositive increased significantly with house infestation among children from stable households, whereas both variables were not significantly associated among children from households exhibiting high mobility within the communities, possibly owing to less consistent exposures. Human infection was clustered by household and at a larger spatial scale, with hotspots of human and vector infection matching areas of higher social vulnerability. These results were integrated in a risk map that shows high-priority areas for targeted interventions oriented to suppress house (re)infestations, detect and treat infected children, and thus reduce the burden of future disease.

Chagas disease is one of the main neglected tropical diseases (NTDs) affecting vulnerable communities in Latin America where transmission by triatomine vectors still occurs. Access to diagnosis and treatment is one of the remaining challenges for sustainable control of Chagas disease in endemic areas. In this study, we integrated the ecological and social determinants of human infection with the spatial component to identify individuals, households and geographic sectors at higher risk of infection. We found that human infection was more prevalent in indigenous people compared to creoles and increased with the abundance of infected vectors and with household social vulnerability (a multidimensional index of poverty). We also found that the social factors modulated the effect of the abundance of infected vectors: vulnerable-household residents were exposed to a higher risk of infection even at low infected-vector abundance, and human mobility within the area determined a lower and more variable exposure to the vector over time. These results were integrated in a risk map that showed high-priority areas, which can be used in designing cost-effective serological screening strategies adapted to resource-constrained areas.

Trypanosoma cruzi transmission dynamics in a synanthropic and domesticated host community

Trypanosoma cruzi is the causative agent of Chagas disease, a Neglected Tropical Disease affecting 8 million people in the Americas. Triatomine hematophagous vectors feed on a high diversity of vertebrate species that can be reservoirs or dead-end hosts, such as avian species refractory to T. cruzi. To understand its transmission dynamics in synanthropic and domesticated species living within villages is essential to quantify disease risk and assess the potential of zooprophylaxis. We developed a SI model of T. cruzi transmission in a multi-host community where vector reproduction and parasite transmission depend on a triatomine blood-feeding rate accounting for vector host preferences and interference while feeding. The model was parameterized to describe T. cruzi transmission in villages of the Yucatan peninsula, Mexico, using the information about Triatoma dimidiata vectors and host populations accumulated over the past 15 years. Extensive analyses of the model showed that dogs are key reservoirs and contributors to human infection, as compared to synanthropic rodents and cats, while chickens or other domesticated avian hosts dilute T. cruzi transmission despite increasing vector abundance. In this context, reducing the number of dogs or increasing avian hosts abundance decreases incidence in humans by up to 56% and 39%, respectively, while combining such changes reduces incidence by 71%. Although such effects are only reached over >10-years periods, they represent important considerations to be included in the design of cost-effective Integrated Vector Management. The concomitant reduction in T. cruzi vector prevalence estimated by simulating these zooprophylactic interventions could indeed complement the removal of colonies from the peridomiciles or the use of insect screens that lower vector indoor abundance by ~60% and ~80%. These new findings reinforce the idea that education and community empowerment to reduce basic risk factors is a cornerstone to reach and sustain the key objective of interrupting Chagas disease intra-domiciliary transmission.

Disentangling Trypanosoma cruzi transmission cycle dynamics through the identification of blood meal sources of natural populations of Triatoma dimidiata in Yucatán, Mexico

Background

In the Yucatán Peninsula, Mexico, Triatoma dimidiata is the main vector of Trypanosoma cruzi, the causative agent of Chagas disease. Little effort has been made to identify blood meal sources of T. dimidiata in natural conditions in this region, although this provides key information to disentangle T. cruzi transmission cycles and dynamics and guide the development of more effective control strategies. We identified the blood meals of a large sample of T. dimidiata bugs collected in different ecotopes simultaneously with the assessment of bug infection with T. cruzi, to disentangle the dynamics of T. cruzi transmission in the region.

Methods

A sample of 248 T. dimidiata bugs collected in three rural villages and in the sylvatic habitat surrounding these villages was used. DNA from each bug midgut was extracted and bug infection with T. cruzi was assessed by PCR. For blood meal identification, we used a molecular assay based on cloning and sequencing following PCR amplification with vertebrate universal primers, and allowing the detection of multiple blood meals in a single bug.

Results

Overall, 28.7% of the bugs were infected with T. cruzi, with no statistical difference between bugs from the villages or from sylvatic ecotopes. Sixteen vertebrate species including domestic, synanthropic and sylvatic animals, were identified as blood meal sources for T. dimidiata. Human, dog and cow were the three main species identified, in bugs collected in the villages as well as in sylvatic ecotopes. Importantly, dog was highlighted as the main blood meal source after human. Dog was also the most frequently identified animal together with human within single bugs, and tended to be associated with the infection of the bugs.

Conclusions

Dog, human and cow were identified as the main mammals involved in the connection of sylvatic and domestic transmission cycles in the Yucatán Peninsula, Mexico. Dog appeared as the most important animal in the transmission pathway of T. cruzi to humans, but other domestic and synanthropic animals, which most were previously reported as important hosts of T. cruzi in the region, were evidenced and should be taken into account as part of integrated control strategies aimed at disrupting parasite transmission.

Polypharmacology in the Treatment of Chagas Disease

The current treatment of Chagas disease is based on monopharmacology where the used drugs have limited efficacy and severe side effects. In order to overcome these limitations, some tools have been described including the development or isolation of new drugs, drug repositioning, and polypharmacology. Here, we review the polypharmacology strategy where compounds belonging to different structural chemotypes were combined in order to affect different biochemical pathways of T. cruzi parasite. Therefore ergosterol biosynthesis inhibitors, anti-inflammatory agents, cardiac dysfunction drugs, trypanothione reductase inhibitors, vitamins, between others, were combined looking for new anti-Chagas treatment. Natural products were also used in the application of this strategy.

Insights from quantitative and mathematical modelling on the proposed WHO 2030 goals for Chagas disease

Chagas disease (CD) persists as one of the neglected tropical diseases (NTDs) with a particularly large impact in the Americas. The World Health Organization (WHO) recently proposed goals for CD elimination as a public health problem to be reached by 2030 by means of achieving intradomiciliary transmission interruption (IDTI), blood transfusion and transplant transmission interruption, diagnostic and treatment scaling-up and prevention and control of congenital transmission. The NTD Modelling Consortium has developed mathematical models to study Trypanosoma cruzi transmission dynamics and the potential impact of control measures. Modelling insights have shown that IDTI is feasible in areas with sustained vector control programmes and no presence of native triatomine vector populations. However, IDTI in areas with native vectors it is not feasible in a sustainable manner. Combining vector control with trypanocidal treatment can reduce the timeframes necessary to reach operational thresholds for IDTI (<2% seroprevalence in children aged <5 years), but the most informative age groups for serological monitoring are yet to be identified. Measuring progress towards the 2030 goals will require availability of vector surveillance and seroprevalence data at a fine scale, and a more active surveillance system, as well as a better understanding of the risks of vector re-colonization and disease resurgence after vector control cessation. Also, achieving scaling-up in terms of access to treatment to the expected levels (75%) will require a substantial increase in screening asymptomatic populations, which is anticipated to become very costly as CD prevalence decreases. Further modelling work includes refining and extending mathematical models (including transmission dynamics and statistical frameworks) to predict transmission at a sub-national scale, and developing quantitative tools to inform IDTI certification, post-certification and re-certification protocols. Potential perverse incentives associated with operational thresholds are discussed. These modelling insights aim to inform discussions on the goals and treatment guidelines for CD.

Spermathecae: Morphofunctional features and correlation with fat bodies and trachea in six species of vectors of Chagas disease

Since spermatheca is able to transport spermatozoa and maintain a specific microenvironment for the storage of viable sperm cells for long periods of time, specific morphofunctional features must be involved in this capacity, and an efficient nutritional and oxygen supply must be required. In this study, we investigated the histological features of spermathecae and fat bodies in six species of three genera of epidemiological importance for Chagas' disease. The association of the reproductive system with the fat bodies and tracheal system was also focused in these species. The reproductive system, tracheae and fat bodies were fixed in 4% formaldehyde, and embedded in glycol methacrylate. The sections were stained with H.E., picrosirius red and Periodic-Acid Schiff methods for morphological analyses. Paraffin-embedded spermatheca sections were submitted to immunofluorescence for detection of V-ATPase. In P. lignarius, R. montenegrensis and R. prolixus, the spermatheca contains a slightly dilated tubular distal portion. In P. megistus and T. tibiamaculata, the spermatheca shows a large bulbous distal portion, and in T. infestans, a large oval-shaped distal portion. In all species, this portion was surrounded by a thin muscular layer, and the epithelial height varied according to the shape of this terminal portion. All spermathecal proximal portions showed simple columnar epithelium surrounded by a thick muscular layer. The epithelial cells of spermathecae showed PAS-positive cytoplasm and V-ATPase immunofluorescence in the apical surface. Tracheoles and polysaccharide-rich fat body cells were found next or in close contact to the oviduct or spermathecal tissues. The results indicate that the spermatheca proximal portion is related to contraction and sperm transport, whose oxygen and energy supply is guaranteed by the associated tracheal branches and fat bodies. In the storage portion, fat bodies and tracheae seem to be crucial for the maintenance of an optimal spermathecal microenvironment and storage of viable sperm cells. The participation of V-ATPase in the spermathecae epithelial cells may contribute for the maintenance of an optimal luminal milieu to spermatozoa, by alkalinization and/or acidification of lumen, similarly to the other epithelial cell types in insects. Further studies are necessary to clarify the role of this proton pump in the spermathecal epithelial cells.

Cytotaxonomy of Trypanosoma cruzi (Chagas, 1909): Differentiation of T. cruzi I (TcI) and T. cruzi II (TcII) Genotypes Using Cytogenetic Markers

Chagas disease is a public health problem caused by the Trypanosoma cruzi, and the T. cruzi I (TcI) and T. cruzi II (TcII) groups are considered important genotypes from the clinical point of view. Currently, the groups need to be molecularly analyzed for their identification; thus, we cytogenetically analyzed these groups with the objective of developing more accessible techniques for the characterization of these parasites. TcI and TcII groups were differentiated by nucleus characterization with lacto-acetic orcein (TcI-nucleus with positive heteropycnosis and TcII-nucleus with negative heteropycnosis), emphasizing the importance of the application of this technique for epidemiological and clinical studies of Chagas disease.

Heterogeneity of Trypanosoma cruzi infection rates in vectors and animal reservoirs in Colombia: a systematic review and meta-analysis

Background

The heterogeneity of Trypanosoma cruzi infection rates among triatomines insects and animal reservoirs has been studied in independent studies, but little information has been systematised to allow pooled and comparative estimates. Unravelling the main patterns of this heterogeneity could contribute to a further understanding of T. cruzi transmission in Colombia.

Methods

A systematic search was conducted in PubMed, Medline, LILACS, Embase, Web of Knowledge, Google Scholar and secondary sources with no filters of language or time and until April 2018. Based on selection criteria, all relevant studies reporting T. cruzi infection rates in reservoirs or triatomines were chosen. For pooled analyses, a random effects model for binomial distribution was used. Heterogeneity among studies is reported as I². Subgroup analyses included: taxonomic classification, ecotope and diagnostic methods. Publication bias and sensitivity analyses were performed.

Results

Overall, 39 studies reporting infection rates in Colombia were found (22 for potential reservoirs and 28 for triatomine insects) for a total sample of 22,838 potential animals and 11,307 triatomines evaluated for T. cruzi infection. We have found evidence of 38/71 different animal species as potential T. cruzi reservoirs and 14/18 species as triatomine vectors for T. cruzi. Among animals, the species with the highest pooled prevalence were opossum (Didelphis marsupialis) with 48.0% (95% CI: 26–71%; I² = 88%, τ² = 0.07, P < 0.01) and domestic dog (Canis lupus familiaris) with 22.0% (95% CI: 4–48%; I² = 96%, τ² = 0.01, P < 0.01). Among triatomines, the highest prevalence was found for Triatoma maculata in the peridomestic ecotope (68.0%, 95% CI: 62–74%; I² = 0%, τ² = 0, P < 0.0001), followed by Rhodnius prolixus (62.0%, 95% CI: 38–84%; I² = 95%, τ² = 0.05, P < 0.01) and Rhodnius pallescens (54.0%, 95% CI: 37–71%; I² = 86%, τ² = 0.035, P < 0.01) in the sylvatic ecotope.

Conclusions

To our knowledge, this is the first systematic and quantitative analyses of triatomine insects and potential animal reservoirs for T. cruzi infection in Colombia. The results highlight a marked heterogeneity between species and provide initial estimates of infection rates heterogeneity.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3541-5) contains supplementary material, which is available to authorized users.

Strategies for tackling Taenia solium taeniosis/cysticercosis: A systematic review and comparison of transmission models, including an assessment of the wider Taeniidae family transmission models

Background

The cestode Taenia solium causes the neglected (zoonotic) tropical disease cysticercosis, a leading cause of preventable epilepsy in endemic low and middle-income countries. Transmission models can inform current scaling-up of control efforts by helping to identify, validate and optimise control and elimination strategies as proposed by the World Health Organization (WHO).

Methodology/Principal findings

A systematic literature search was conducted using the PRISMA approach to identify and compare existing T. solium transmission models, and related Taeniidae infection transmission models. In total, 28 modelling papers were identified, of which four modelled T. solium exclusively. Different modelling approaches for T. solium included deterministic, Reed-Frost, individual-based, decision-tree, and conceptual frameworks. Simulated interventions across models agreed on the importance of coverage for impactful effectiveness to be achieved.

Other Taeniidae infection transmission models comprised force-of-infection (FoI), population-based (mainly Echinococcus granulosus) and individual-based (mainly E. multilocularis) modelling approaches. Spatial structure has also been incorporated (E. multilocularis and Taenia ovis) in recognition of spatial aggregation of parasite eggs in the environment and movement of wild animal host populations.

Conclusions/Significance

Gaps identified from examining the wider Taeniidae family models highlighted the potential role of FoI modelling to inform model parameterisation, as well as the need for spatial modelling and suitable structuring of interventions as key areas for future T. solium model development. We conclude that working with field partners to address data gaps and conducting cross-model validation with baseline and longitudinal data will be critical to building consensus-led and epidemiological setting-appropriate intervention strategies to help fulfil the WHO targets.

Taenia solium infection in humans (taeniosis and neurocysticercosis) and pigs (cysticercosis) presents a significant global public health and economic challenge. The World Health Organization has called for validated strategies and wider consensus on which strategies are suitable for different epidemiological settings to support successful T. solium control and elimination efforts. Transmission models can be used to inform these strategies. Therefore, a modelling review was undertaken to assess the current state and gaps relating to T. solium epidemiological modelling. The literature surrounding models for other Taeniidae family infections was also considered, identifying approaches to aid further development of existing T. solium models. A variety of different modelling approaches have been used for T. solium including differences in structural and parametric assumptions associated with T. solium transmission biology. Despite these differences, all models agreed on the importance of coverage on intervention effectiveness. Other Taeniidae family models highlighted the need for incorporating spatial structure when necessary to capture aggregation of transmission stages in the environment and movement of animal hosts.

In vitro antiprotozoal activity of some medicinal plants against sleeping sickness, Chagas disease and leishmaniasis

AIM

Antiprotozoal activity of 36 medicinal plants was evaluated.

MATERIALS & METHODS

In vitro potency against Trypanosoma brucei brucei, T. b. rhodesiense, T. cruzi and Leishmania infantum beside cytotoxicity on MRC-5 fibroblasts were determined.

RESULTS & CONCLUSION

Maytenus parviflora showed the highest activity against T. b. brucei (IC₅₀ of 0.6 μg/ml) and T. b. rhodesiense (IC₅₀ of 0.5 μg/ml) with low cytotoxicity (CC₅₀ of 30 μg/ml). Saussurea costus and Commiphora wightii, showed pronounced potency against T. cruzi with an IC₅₀ of 3.6 and 2.5 μg/ml, respectively. Jatropha pelargonifolia and Solanum villosum exhibited pronounced activity toward L. infantum with an IC₅₀ of 3.2 and 2.0 μg/ml, respectively. M. parviflora, S. costus, C. wightii, J. pelargonifolia and S. villosum showed relevant selectivity.

Non-randomized controlled trial of the long-term efficacy of an Ecohealth intervention against Chagas disease in Yucatan, Mexico

Non-domiciliated intrusive triatomine vectors are responsible for a low but significant transmission of Trypanosoma cruzi to humans. Their control is a challenge as insecticide spraying is of limited usefulness, and alternative strategies need to be developed for a sustainable control. We performed a non-randomized controlled trial of an Ecohealth intervention based on window insect screens and community participation to reduce house infestation by Triatoma dimidiata in two rural villages in Yucatan, Mexico. Efficacy of the intervention was measured over a three years follow-up period and entomological indicators showed that the proportion of triatomines found inside houses was significantly reduced in houses with insect screens, which effectively kept more bugs on the outside of houses. Using a previously developed model linking entomological data to the prevalence of infection in human, we predicted that the intervention would lead to a 32% reduction in yearly incidence and in the prevalence of T. cruzi infection. The cost for the coverage of all the windows of a house was of comparable magnitude to what families currently spend on various domestic insecticide, and most screens were still in good conditions after three years. In conclusion, the Ecohealth approach proposed here is effective for the long-term and sustainable control of intrusive T. dimidiata vectors in the Yucatan peninsula, Mexico. This strategy may also be easily adapted to other intrusive triatomine species as well as other regions/countries with comparable eco-epidemiological settings, and would be an excellent component of a larger integrated program for the control of a variety of other vector-borne diseases, bringing additional benefits to the communities. Our results should encourage a further scaling-up of our implementation strategy in additional villages in the region.

Looking for combination of benznidazole and Trypanosoma cruzi-triosephosphate isomerase inhibitors for Chagas disease treatment

BACKGROUND

The current chemotherapy for Chagas disease is based on monopharmacology with low efficacy and drug tolerance. Polypharmacology is one of the strategies to overcome these limitations.

OBJECTIVES

Study the anti-Trypanosoma cruzi activity of associations of benznidazole (Bnz) with three new synthetic T. cruzi-triosephosphate isomerase inhibitors, 2, 3, and 4, in order to potentiate their actions.

METHODS

The in vitro effect of the drug combinations were determined constructing the corresponding isobolograms. In vivo activities were assessed using an acute murine model of Chagas disease evaluating parasitaemias, mortalities and IgG anti-T. cruzi antibodies.

FINDINGS

The effect of Bnz combined with each of these compounds, on the growth of epimastigotes, indicated an additive action or a synergic action, when combining it with 2 or 3, respectively, and an antagonic action when combining it with 4. In vivo studies, for the two chosen combinations, 2 or 3 plus one fifth equivalent of Bnz, showed that Bnz can also potentiate the in vivo therapeutic effects. For both combinations a decrease in the number of trypomastigote and lower levels of anti-T. cruzi IgG-antibodies were detected, as well clear protection against death.

MAIN CONCLUSIONS

These results suggest the studied combinations could be used in the treatment of Chagas disease.

Detailed ecological associations of triatomines revealed by metabarcoding and next-generation sequencing: implications for triatomine behavior and Trypanosoma cruzi transmission cycles

Trypanosoma cruzi is the agent of Chagas disease, transmitted by hematophagous triatomine vectors. Establishing transmission cycles is key to understand the epidemiology of the disease, but integrative assessments of ecological interactions shaping parasite transmission are still limited. Current approaches also lack sensitivity to assess the full extent of this ecological diversity. Here we developed a metabarcoding approach based on next-generation sequencing to identify triatomine gut microbiome, vertebrate feeding hosts, and parasite diversity and their potential interactions. We detected a dynamic microbiome in Triatoma dimidiata, including 23 bacterial orders, which differed according to blood sources. Fourteen vertebrate species served as blood sources, corresponding to domestic, synantropic and sylvatic species, although four (human, dog, cow and mice) accounted for over 50% of blood sources. Importantly, bugs fed on multiple hosts, with up to 11 hosts identified per bug, indicating very frequent host-switching. A high clonal diversity of T. cruzi was detected, with up to 20 haplotypes per bug. This analysis provided much greater sensitivity to detect multiple blood meals and multiclonal infections with T. cruzi, which should be taken into account to develop transmission networks, and characterize the risk for human infection, eventually leading to a better control of disease transmission.

Models of Disease Vector Control: When Can Aggressive Initial Intervention Lower Long-Term Cost?

Insecticide spraying of housing units is an important control measure for vector-borne infections such as Chagas disease. As vectors may invade both from other infested houses and sylvatic areas and as the effectiveness of insecticide wears off over time, the dynamics of (re)infestations can be approximated by [Formula: see text]-type models with a reservoir, where housing units are treated as hosts, and insecticide spraying corresponds to removal of hosts. Here, we investigate three ODE-based models of this type. We describe a dual-rate effect where an initially very high spraying rate can push the system into a region of the state space with low endemic levels of infestation that can be maintained in the long run at relatively moderate cost, while in the absence of an aggressive initial intervention the same average cost would only allow a much less significant reduction in long-term infestation levels. We determine some sufficient and some necessary conditions under which this effect occurs and show that it is robust in models that incorporate some heterogeneity in the relevant properties of housing units.

Fe3+chelating quinoline–hydrazone hybrids with proven cytotoxicity, leishmanicidal, and trypanocidal activities

Neglected tropical diseases cause great concern in developing countries where there are millions of reported infected humans. Our calculations support a direct relationship between biological activity and the Fe³⁺chelating ability of the shown set of quinoline–hydrazone hybrids.

Evolutionary ecology of Chagas disease; what do we know and what do we need?

The aetiological agent of Chagas disease, Trypanosoma cruzi, is a key human pathogen afflicting most populations of Latin America. This vectorborne parasite is transmitted by haematophageous triatomines, whose control by large‐scale insecticide spraying has been the main strategy to limit the impact of the disease for over 25 years. While those international initiatives have been successful in highly endemic areas, this systematic approach is now challenged by the emergence of insecticide resistance and by its low efficacy in controlling species that are only partially adapted to human habitat. In this contribution, we review evidences that Chagas disease control shall now be entering a second stage that will rely on a better understanding of triatomines adaptive potential, which requires promoting microevolutionary studies and –omic approaches. Concomitantly, we show that our knowledge of the determinants of the evolution of T. cruzi high diversity and low virulence remains too limiting to design evolution‐proof strategies, while such attributes may be part of the future of Chagas disease control after the 2020 WHO's target of regional elimination of intradomiciliary transmission has been reached. We should then aim at developing a theory of T. cruzi virulence evolution that we anticipate to provide an interesting enrichment of the general theory according to the specificities of transmission of this very generalist stercorarian trypanosome. We stress that many ecological data required to better understand selective pressures acting on vector and parasite populations are already available as they have been meticulously accumulated in the last century of field research. Although more specific information will surely be needed, an effective research strategy would be to integrate data into the conceptual and theoretical framework of evolutionary ecology and life‐history evolution that provide the quantitative backgrounds necessary to understand and possibly anticipate adaptive responses to public health interventions.

Triclosan-caffeic acid hybrids: Synthesis, leishmanicidal, trypanocidal and cytotoxic activities

The synthesis, cytotoxicity, anti-leishmanial and anti-trypanosomal activities of twelve triclosan-caffeic acid hybrids are described herein. The structure of the synthesized products was elucidated by a combination of spectrometric analyses. The synthesized compounds were evaluated against amastigotes forms of L. (V) panamensis, which is the most prevalent Leishmania species in Colombia, and against Trypanosoma cruzi, which is the pathogenic species to humans. Cytotoxicity was evaluated against human U-937 macrophages. Eight compounds were active against L. (V) panamensis (18-23, 26 and 30) and eight of them against T. cruzi (19-22, 24 and 28-30) with EC₅₀ values lower than 40 μM. Compounds 19-22, 24 and 28-30 showed higher activities than benznidazole (BNZ). Esters 19 and 21 were the most active compounds for both L. (V) panamensis and T. cruzi with 3.82 and 11.65 μM and 8.25 and 8.69 μM, respectively. Compounds 19-22, 24 and 28-30 showed higher activities than benznidazole (BNZ). Most of the compounds showed antiprotozoal activity and with exception of 18, 26 and 28, the remaining compounds were toxic for mammalian cells, yet they have potential to be considered as candidates for anti-trypanosomal and anti-leishmanial drug development. The activity is dependent on the length of the alkyl linker with compound 19, bearing a four-carbon alkyl chain, the most performing hybrid. In general, hydroxyl groups increase both activity and cytotoxicity and the presence of the double bond in the side chain is not decisive for cytotoxicity and anti-protozoal activity.

Pacemaker Implants in Children and Adolescents with Chagas Disease in Brazil: 18-Year Incidence

Background:

Chagas disease continues to be a serious public health problem, and accounts for 25-30% of the indications for cardiac stimulation in Brazil.

Objective:

To assess clinical and epidemiological characteristics of patients with Chagas disease, younger than 18 years, who had undergone pacemaker implantation in Brazil between 1994 and 2011, and its temporal trend.

Methods:

This was a cross-sectional analysis of data from the Brazilian Pacemaker Registry database. The following variables were analyzed: year when pacemaker was implanted, location, age, sex, ethnic group, functional class and the main electrocardiographic findings at baseline.

Results:

In a total of 183,123 implants performed between 1994 and 2011, 214 implants of cardiac stimulation device in Chagas disease patients aged younger than 18 years were identified. Mean age at implantation was 5.6 ± 6.2 years. Second- and third-degree atrioventricular blocks corresponded to 71% of indications for pacemaker implantation. Fifty-six percent of the procedures were performed in the southeast region. Regarding the total number of pacemaker implants per year, there was a remarkable increase in the implants for all causes. However, time series analysis of the implants in Chagas disease patients younger than 18 years revealed a significant reduction in the annual number of implants.

Conclusion:

There has been an important reduction in the number of pacemaker implantations among children and adolescents with Chagas disease, suggesting a reduction in the vertical transmission of the parasite.

Epidemiological modeling of Trypanosoma cruzi: Low stercorarian transmission and failure of host adaptive immunity explain the frequency of mixed infections in humans

People living in areas with active vector-borne transmission of Chagas disease have multiple contacts with its causative agent, Trypanosoma cruzi. Reinfections by T. cruzi are possible at least in animal models leading to lower or even hardly detectable parasitaemia. In humans, although reinfections are thought to have major public health implications by increasing the risk of chronic manifestations of the disease, there is little quantitative knowledge about their frequency and the timing of parasite re-inoculation in the course of the disease. Here, we implemented stochastic agent-based models i) to estimate the rate of re-inoculation in humans and ii) to assess how frequent are reinfections during the acute and chronic stages of the disease according to alternative hypotheses on the adaptive immune response following a primary infection. By using a hybrid genetic algorithm, the models were fitted to epidemiological data of Argentinean rural villages where mixed infections by different genotypes of T. cruzi reach 56% in humans. To explain this percentage, the best model predicted 0.032 (0.008-0.042) annual reinfections per individual with 98.4% of them occurring in the chronic phase. In addition, the parasite escapes to the adaptive immune response mounted after the primary infection in at least 20% of the events of re-inoculation. With these low annual rates, the risks of reinfection during the typically long chronic stage of the disease stand around 14% (4%-18%) and 60% (21%-70%) after 5 and 30 years, with most individuals being re-infected 1-3 times overall. These low rates are better explained by the weak efficiency of the stercorarian mode of transmission than a highly efficient adaptive immune response. Those estimates are of particular interest for vaccine development and for our understanding of the higher risk of chronic disease manifestations suffered by infected people living in endemic areas.

Modeling Chagas disease in Chile: From vector to congenital transmission

Chagaś disease is a human health problem in Latin America. It is highly prevalent in northern Chile between the Arica-Parinacota and Coquimbo regions, with reported incidence of 3-11/100000 inhabitants and mortality of 0.3-0.4/100000. The interruption of vector transmission was reported in 1999 by means of the elimination of the primary vector, Triatoma infestans, from human dwellings, thus the epidemiologic dynamics of this disease should be modified. Here we model the dynamics of Chagaś disease based on previous models for vector and congenital transmission, propose a model that includes both transmission forms and perform simulations. We derive useful relationships for the reproductive number (R₀) showing that it may be expressed as the sum of the vector (R_0V) and congenital (R_0C) contributions. The vector contribution is larger than the congenital one; without the former Chagaś disease vanishes exponentially in two to three generations. Sensitivity analyses showed that the main parameters that intervene are the human bite rate, the density of vectors per human and the mortality rate of the insect vectors. Our model showed that the success of the eradication of Chagaś disease is based on the interruption of domestic transmission. Once this is obtained, the control strategies should focus on avoiding the domiciliation of wild vectors, re-colonization by the primary vector, and an adequate coverage of congenital case treatment.

Comparison and validation of two computational models of Chagas disease: A thirty year perspective from Venezuela

BACKGROUND

Mathematical models can help aid public health responses to Chagas disease. Models are typically developed to fulfill a particular need, and comparing outputs from different models addressing the same question can help identify the strengths and weaknesses of the models in answering particular questions, such as those for achieving the 2020 goals for Chagas disease.

METHODS

Using two separately developed models (PHICOR/CIDMA model and Princeton model), we simulated dynamics for domestic transmission of Trypanosoma cruzi (T. cruzi). We compared how well the models targeted the last 9 years and last 19 years of the 1968-1998 historical seroprevalence data from Venezuela.

RESULTS

Both models were able to generate the T. cruzi seroprevalence for the next time period within reason to the historical data. The PHICOR/CIDMA model estimates of the total population seroprevalence more closely followed the trends seen in the historic data, while the Princeton model estimates of the age-specific seroprevalence more closely followed historic trends when simulating over 9 years. Additionally, results from both models overestimated T. cruzi seroprevalence among younger age groups, while underestimating the seroprevalence of T. cruzi in older age groups.

CONCLUSION

The PHICOR/CIDMA and Princeton models differ in level of detail and included features, yet both were able to generate the historical changes in T. cruzi seroprevalence in Venezuela over 9 and 19-year time periods. Our model comparison has demonstrated that different model structures can be useful in evaluating disease transmission dynamics and intervention strategies.

Relationships between altitude, triatomine (Triatoma dimidiata) immune response and virulence of Trypanosoma cruzi, the causal agent of Chagas' disease

Little is known about how the virulence of a human pathogen varies in the environment it shares with its vector. This study focused on whether the virulence of Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae), the causal agent of Chagas' disease, is related to altitude. Accordingly, Triatoma dimidiata (Hemiptera: Reduviidae) specimens were collected at three different altitudes (300, 700 and 1400 m a.s.l.) in Chiapas, Mexico. The parasite was then isolated to infect uninfected T. dimidiata from the same altitudes, as well as female CD-1 mice. The response variables were phenoloxidase (PO) activity, a key insect immune response, parasitaemia in mice, and amastigote numbers in the heart, oesophagus, gastrocnemius and brain of the rodents. The highest levels of PO activity, parasitaemia and amastigotes were found for Tryp. cruzi isolates sourced from 700 m a.s.l., particularly in the mouse brain. A polymerase chain reaction-based analysis indicated that all Tryp. cruzi isolates belonged to a Tryp. cruzi I lineage. Thus, Tryp. cruzi from 700 m a.s.l. may be more dangerous than sources at other altitudes. At this altitude, T. dimidiata is more common, apparently because the conditions are more beneficial to its development. Control strategies should focus activity at altitudes around 700 m a.s.l., at least in relation to the region of the present study sites.

Structural isomerism of Ru(ii)-carbonyl complexes: synthesis, characterization and their antitrypanosomal activities

New complexes with the formula [RuCl(CO)(dppb)(N–N)]PF₆ were prepared by varying the CO position as well as the diimine ligand.

DNA Microarray Detection of 18 Important Human Blood Protozoan Species

Background

Accurate detection of blood protozoa from clinical samples is important for diagnosis, treatment and control of related diseases. In this preliminary study, a novel DNA microarray system was assessed for the detection of Plasmodium, Leishmania, Trypanosoma, Toxoplasma gondii and Babesia in humans, animals, and vectors, in comparison with microscopy and PCR data. Developing a rapid, simple, and convenient detection method for protozoan detection is an urgent need.

Methodology/Principal Findings

The microarray assay simultaneously identified 18 species of common blood protozoa based on the differences in respective target genes. A total of 20 specific primer pairs and 107 microarray probes were selected according to conserved regions which were designed to identify 18 species in 5 blood protozoan genera. The positive detection rate of the microarray assay was 91.78% (402/438). Sensitivity and specificity for blood protozoan detection ranged from 82.4% (95%CI: 65.9% ~ 98.8%) to 100.0% and 95.1% (95%CI: 93.2% ~ 97.0%) to 100.0%, respectively. Positive predictive value (PPV) and negative predictive value (NPV) ranged from 20.0% (95%CI: 2.5% ~ 37.5%) to 100.0% and 96.8% (95%CI: 95.0% ~ 98.6%) to 100.0%, respectively. Youden index varied from 0.82 to 0.98. The detection limit of the DNA microarrays ranged from 200 to 500 copies/reaction, similar to PCR findings. The concordance rate between microarray data and DNA sequencing results was 100%.

Conclusions/Significance

Overall, the newly developed microarray platform provides a convenient, highly accurate, and reliable clinical assay for the determination of blood protozoan species.

More than 1 billion people are infected with blood protozoan diseases worldwide. The most common blood protozoa in humans, animals, and vectors include Plasmodium, Leishmania, Trypanosoma, Toxoplasma gondii and Babesia. Due to similar morphology among different blood protozoan species, misdiagnosis always occurs. Most molecular techniques are only carried out in laboratories, with a small number of samples detected simultaneously. Meanwhile, common detection methods may not be convenient for field investigation of large amounts of samples. In order to better manage blood protozoan infection, proper tools are required for the monitoring of these pathogens. Here, a comprehensive and sensitive DNA microarray was developed and tested, which allowed the parallel detection of 18 blood protozoan species.

Serological Diagnosis of Chronic Chagas Disease: Is It Time for a Change?

Chagas disease has spread to areas that are nonendemic for the disease with human migration. Since no single reference standard test is available, serological diagnosis of chronic Chagas disease requires at least two tests. New-generation techniques have significantly improved the accuracy of Chagas disease diagnosis by the use of a large mixture of recombinant antigens with different detection systems, such as chemiluminescence. The aim of the present study was to assess the overall accuracy of a new-generation kit, the Architect Chagas (cutoff, ≥1 sample relative light units/cutoff value [S/CO]), as a single technique for the diagnosis of chronic Chagas disease. The Architect Chagas showed a sensitivity of 100% (95% confidence interval [CI], 99.5 to 100%) and a specificity of 97.6% (95% CI, 95.2 to 99.9%). Five out of six false-positive serum samples were a consequence of cross-reactivity with Leishmania spp., and all of them achieved results of <5 S/CO. We propose the Architect Chagas as a single technique for screening in blood banks and for routine diagnosis in clinical laboratories. Only gray-zone and positive sera with a result of ≤6 S/CO would need to be confirmed by a second serological assay, thus avoiding false-positive sera and the problem of cross-reactivity with Leishmania species. The application of this proposal would result in important savings in the cost of Chagas disease diagnosis and therefore in the management and control of the disease.

Amazonian Triatomine Biodiversity and the Transmission of Chagas Disease in French Guiana: In Medio Stat Sanitas

The effects of biodiversity on the transmission of infectious diseases now stand as a cornerstone of many public health policies. The upper Amazonia and Guyana shield are hot-spots of biodiversity that offer genuine opportunities to explore the relationship between the risk of transmission of Chagas disease and the diversity of its triatomine vectors. Over 730 triatomines were light-trapped in four geomorphological landscapes shaping French-Guiana, and we determined their taxonomic status and infection by Trypanosoma cruzi. We used a model selection approach to unravel the spatial and temporal variations in species abundance, diversity and infection. The vector community in French-Guiana is typically made of one key species (Panstrongylus geniculatus) that is more abundant than three secondary species combined (Rhodnius pictipes, Panstrongylus lignarius and Eratyrus mucronatus), and four other species that complete the assemblage. Although the overall abundance of adult triatomines does not vary across French-Guiana, their diversity increases along a coastal-inland gradient. These variations unravelled a non-monotonic relationship between vector biodiversity and the risk of transmission of Chagas disease, so that intermediate biodiversity levels are associated with the lowest risks. We also observed biannual variations in triatomine abundance, representing the first report of a biannual pattern in the risk of Chagas disease transmission. Those variations were highly and negatively correlated with the average monthly rainfall. We discuss the implications of these patterns for the transmission of T. cruzi by assemblages of triatomine species, and for the dual challenge of controlling Amazonian vector communities that are made of both highly diverse and mostly intrusive species.

Increased mortality attributed to Chagas disease: a systematic review and meta-analysis

BACKGROUND

The clinical outcomes associated with Chagas disease remain poorly understood. In addition to the burden of morbidity, the burden of mortality due to Trypanosoma cruzi infection can be substantial, yet its quantification has eluded rigorous scrutiny. This is partly due to considerable heterogeneity between studies, which can influence the resulting estimates. There is a pressing need for accurate estimates of mortality due to Chagas disease that can be used to improve mathematical modelling, burden of disease evaluations, and cost-effectiveness studies.

METHODS

A systematic literature review was conducted to select observational studies comparing mortality in populations with and without a diagnosis of Chagas disease using the PubMed, MEDLINE, EMBASE, Web of Science and LILACS databases, without restrictions on language or date of publication. The primary outcome of interest was mortality (as all-cause mortality, sudden cardiac death, heart transplant or cardiovascular deaths). Data were analysed using a random-effects model to obtain the relative risk (RR) of mortality, the attributable risk percent (ARP), and the annual mortality rates (AMR). The statistic I(2) (proportion of variance in the meta-analysis due to study heterogeneity) was calculated. Sensitivity analyses and publication bias test were also conducted.

RESULTS

Twenty five studies were selected for quantitative analysis, providing data on 10,638 patients, 53,346 patient-years of follow-up, and 2739 events. Pooled estimates revealed that Chagas disease patients have significantly higher AMR compared with non-Chagas disease patients (0.18 versus 0.10; RR = 1.74, 95% CI 1.49-2.03). Substantial heterogeneity was found among studies (I(2) = 67.3%). The ARP above background mortality was 42.5%. Through a sub-analysis patients were classified by clinical group (severe, moderate, asymptomatic). While RR did not differ significantly between clinical groups, important differences in AMR were found: AMR = 0.43 in Chagas vs. 0.29 in non-Chagas patients (RR = 1.40, 95% CI 1.21-1.62) in the severe group; AMR = 0.16 (Chagas) vs. 0.08 (non-Chagas) (RR = 2.10, 95% CI 1.52-2.91) in the moderate group, and AMR = 0.02 vs. 0.01 (RR = 1.42, 95% CI 1.14-1.77) in the asymptomatic group. Meta-regression showed no evidence of study-level covariates on the effect size. Publication bias was not statistically significant (Egger's test p=0.08).

CONCLUSIONS

The results indicate a statistically significant excess of mortality due to Chagas disease that is shared among both symptomatic and asymptomatic populations.

The multiple and complex and changeable scenarios of the Trypanosoma cruzi transmission cycle in the sylvatic environment

In this study, we report and discuss the results generated from over 20 years of studies of the Trypanosoma cruzi sylvatic transmission cycle. Our results have uncovered new aspects and reviewed old concepts on issues including reservoirs, true generalist species, association of mammalian species with distinct discrete typing units - DTUs, distribution of T. cruzi genotypes in the wild, mixed infections, and T. cruzi transmission ecology. Using parasitological and serological tests, we examined T. cruzi infection in 7,285 mammalian specimens from nine mammalian orders dispersed all over the Brazilian biomes. The obtained T. cruzi isolates were characterized by mini-exon gene sequence polymorphism and PCR RFLP to identify DTUs. Infection by T. cruzi was detected by serological methods in 20% of the examined animals and isolated from 41% of those infected, corresponding to 8% of all the examined mammals. Each mammal taxon responded uniquely to T. cruzi infection. Didelphis spp. are able to maintain high and long-lasting parasitemias (positive hemocultures) caused by TcI but maintain and rapidly control parasitemias caused by TcII to almost undetectable levels. In contrast, the tamarin species Leontopithecus rosalia and L. chrysomelas maintain long-lasting and high parasitemias caused by TcII similarly to Philander sp. The coati Nasua nasua maintains high parasitemias by both parental T. cruzi DTUs TcI or TcII and by TcII/TcIV (formerly Z3) at detectable levels. Wild and domestic canidae seem to display only a short period of reservoir competence. T. cruzi infection was demonstrated in the wild canid species Cerdocyon thous and Chrysocyon brachyurus, and positive hemoculture was obtained in one hyper carnivore species (Leopardus pardalis), demonstrating that T. cruzi transmission is deeply immersed in the trophic net. T. cruzi DTU distribution in nature did not exhibit any association with a particular biome or habitat. TcI predominates throughout (58% of the T. cruzi isolates); however, in spite of being significantly less frequent (17%), TcII is also widely distributed. Concomitant DTU infection occurred in 16% of infected mammals of all biomes and included arboreal and terrestrial species, as well as bats. TcI/TcII concomitant infection was the most common and widely dispersed, with mixed TcI/TcII infections especially common in coatis and in Didelphimorphia. The second most common pattern of concomitant infection was TcI/TcIV, observed in Chiroptera, Didelphimorphia and Primates. Taken together, our results demonstrate the complexity of T. cruzi reservoir system and its transmission strategies, indicating that there is considerably more to be learned regarding ecology of T. cruzi.

Heterogeneous infectiousness in guinea pigs experimentally infected with Trypanosoma cruzi

Guinea pigs are important reservoirs of Trypanosoma cruzi, the causative parasite of Chagas disease, and in the Southern Cone of South America, transmission is mediated mainly by the vector Triatoma infestans. Interestingly, colonies of Triatoma infestans captured from guinea pig corrals sporadically have infection prevalence rates above 80%. Such high values are not consistent with the relatively short 7-8 week parasitemic period that has been reported for guinea pigs in the literature. We experimentally measured the infectious periods of a group of T. cruzi-infected guinea pigs by performing xenodiagnosis and direct microscopy each week for one year. Another group of infected guinea pigs received only direct microscopy to control for the effect that inoculation by triatomine saliva may have on parasitemia in the host. We observed infectious periods longer than those previously reported in a number of guinea pigs from both the xenodiagnosis and control groups. While some guinea pigs were infectious for a short time, other "super-shedders" were parasitemic up to 22 weeks after infection, and/or positive by xenodiagnosis for a year after infection. This heterogeneity in infectiousness has strong implications for T. cruzi transmission dynamics and control, as super-shedder guinea pigs may play a disproportionate role in pathogen spread.

Host switching vs. host sharing in overlapping sylvatic Trypanosoma cruzi transmission cycles

The principle of competitive exclusion is well established for multiple populations competing for the same resource, and simple models for multistrain infection exhibit it as well when cross-immunity precludes coinfections. However, multiple hosts provide niches for different pathogens to occupy simultaneously. This is the case for the vector-borne parasite Trypanosoma cruzi in overlapping sylvatic transmission cycles in the Americas, where it is enzootic. This study uses cycles in the USA involving two different hosts but the same vector species as a context for the study of the mechanisms behind the communication between the two cycles. Vectors dispersing in search of new hosts may be considered to move between the two cycles (host switching) or, more simply, to divide their time between the two host types (host sharing). Analysis considers host switching as an intermediate case between isolated cycles and intermingled cycles (host sharing) in order to examine the role played by the host-switching rate in permitting coexistence of multiple strains in a single-host population. Results show that although the population dynamics (demographic equilibria) in host-switching models align well with those in the limiting models (host sharing or isolated cycles), infection dynamics differ significantly, in ways that sometimes illuminate the underlying epidemiology (such as differing host susceptibilities to infection) and sometimes reveal model limitations (such as host switching dominating the infection dynamics). Numerical work suggests that the model explains the trace presence of TcI in raccoons but not the more significant co-persistence observed in woodrats.

Intrusive versus domiciliated triatomines and the challenge of adapting vector control practices against Chagas disease

Chagas disease prevention remains mostly based on triatomine vector control to reduce or eliminate house infestation with these bugs. The level of adaptation of triatomines to human housing is a key part of vector competence and needs to be precisely evaluated to allow for the design of effective vector control strategies. In this review, we examine how the domiciliation/intrusion level of different triatomine species/populations has been defined and measured and discuss how these concepts may be improved for a better understanding of their ecology and evolution, as well as for the design of more effective control strategies against a large variety of triatomine species. We suggest that a major limitation of current criteria for classifying triatomines into sylvatic, intrusive, domiciliary and domestic species is that these are essentially qualitative and do not rely on quantitative variables measuring population sustainability and fitness in their different habitats. However, such assessments may be derived from further analysis and modelling of field data. Such approaches can shed new light on the domiciliation process of triatomines and may represent a key tool for decision-making and the design of vector control interventions.