Modelling historical changes in the force-of-infection of Chagas disease to inform control and elimination programmes: application in Colombia

Privileged small molecules against neglected tropical diseases: A perspective from structure activity relationships

Neglected tropical diseases (NTDs) comprise diverse infections with more incidence in tropical/sub-tropical areas. In spite of preventive and therapeutic achievements, NTDs are yet serious threats to the public health. Epidemiological reports of world health organization (WHO) indicate that more than 1.5 billion people are afflicted with at least one NTD type. Among NTDs, leishmaniasis, chagas disease (CD) and human African trypanosomiasis (HAT) result in substantial morbidity and death, particularly within impoverished countries. The statistical facts call for robust efforts to manage the NTDs. Currently, most of the anti-NTD drugs are engaged with drug resistance, lack of efficient vaccines, limited spectrum of pharmacological effect and adverse reactions. To circumvent the issue, numerous scientific efforts have been directed to the synthesis and pharmacological development of chemical compounds as anti-infectious agents. A survey of the anti-NTD agents reveals that the majority of them possess privileged nitrogen, sulfur and oxygen-based heterocyclic structures. In this review, recent achievements in anti-infective small molecules against parasitic NTDs are described, particularly from the SAR (Structure activity relationship) perspective. We also explore current advocating strategies to extend the scope of anti-NTD agents.

The Hidden Hand of Asymptomatic Infection Hinders Control of Neglected Tropical Diseases: A Modeling Analysis

BACKGROUND

Neglected tropical diseases are responsible for considerable morbidity and mortality in low-income populations. International efforts have reduced their global burden, but transmission is persistent and case-finding-based interventions rarely target asymptomatic individuals.

METHODS

We develop a generic mathematical modeling framework for analyzing the dynamics of visceral leishmaniasis in the Indian sub-continent (VL), gambiense sleeping sickness (gHAT), and Chagas disease and use it to assess the possible contribution of asymptomatics who later develop disease (pre-symptomatics) and those who do not (non-symptomatics) to the maintenance of infection. Plausible interventions, including active screening, vector control, and reduced time to detection, are simulated for the three diseases.

RESULTS

We found that the high asymptomatic contribution to transmission for Chagas and gHAT and the apparently high basic reproductive number of VL may undermine long-term control. However, the ability to treat some asymptomatics for Chagas and gHAT should make them more controllable, albeit over relatively long time periods due to the slow dynamics of these diseases. For VL, the toxicity of available therapeutics means the asymptomatic population cannot currently be treated, but combining treatment of symptomatics and vector control could yield a quick reduction in transmission.

CONCLUSIONS

Despite the uncertainty in natural history, it appears there is already a relatively good toolbox of interventions to eliminate gHAT, and it is likely that Chagas will need improvements to diagnostics and their use to better target pre-symptomatics. The situation for VL is less clear, and model predictions could be improved by additional empirical data. However, interventions may have to improve to successfully eliminate this disease.

Oral Chagas Disease in Colombia-Confirmed and Suspected Routes of Transmission

Chagas disease (CD) remains endemic throughout many regions of Colombia despite implementing decades of vector control strategies in several departments. Some regions have had a significant decrease in vectorial transmission, but the oral ingestion of Trypanosoma cruzi through consumption of contaminated food and drink products is increasingly described. This form of transmission has important public health relevance in Colombia due to an increase in reported acute CD cases and clinical manifestations that often lead to significant morbidity and mortality. Oral CD in Colombia has been associated with the consumption of contaminated fruit juices, such as palm wine, sugar cane, or tangerine juice and water for consumption, or contaminated surfaces where food has been prepared. Another interesting route of oral transmission includes ingestion of unbeknownst infected armadillos' blood, which is related to a traditional medicine practice in Colombia. Some earlier reports have also implemented consumption of infected bush meat as a source, but this is still being debated. Within the Amazon Basin, oral transmission is now considered the principal cause of acute CD in these regions. Furthermore, new cases of acute CD are now being seen in departments where CD has not been documented, and triatomine vectors are not naturally found, thus raising suspicion for oral transmission. The oral CD could also be considered a food-borne zoonosis, and odoriferous didelphid secretions have been implemented in contaminating the human dwelling environment, increasing the risk of consumption of infectious metacyclic trypomastigotes. In this article, we will discuss the complex transmission dynamics of oral CD in Colombia and further examine the unique clinical manifestations of this route of infection. New insights into the oral transmission of Trypanosoma cruzi are being discovered in Colombia, which can help bring increased awareness and a better understanding of this neglected tropical disease to reduce the burden of CD throughout Latin America.

From serological surveys to disease burden: a modelling pipeline for Chagas disease

In 2012, the World Health Organization (WHO) set the elimination of Chagas disease intradomiciliary vectorial transmission as a goal by 2020. After a decade, some progress has been made, but the new 2021-2030 WHO roadmap has set even more ambitious targets. Innovative and robust modelling methods are required to monitor progress towards these goals. We present a modelling pipeline using local seroprevalence data to obtain national disease burden estimates by disease stage. Firstly, local seroprevalence information is used to estimate spatio-temporal trends in the Force-of-Infection (FoI). FoI estimates are then used to predict such trends across larger and fine-scale geographical areas. Finally, predicted FoI values are used to estimate disease burden based on a disease progression model. Using Colombia as a case study, we estimated that the number of infected people would reach 506 000 (95% credible interval (CrI) = 395 000-648 000) in 2020 with a 1.0% (95%CrI = 0.8-1.3%) prevalence in the general population and 2400 (95%CrI = 1900-3400) deaths (approx. 0.5% of those infected). The interplay between a decrease in infection exposure (FoI and relative proportion of acute cases) was overcompensated by a large increase in population size and gradual population ageing, leading to an increase in the absolute number of Chagas disease cases over time. This article is part of the theme issue 'Challenges and opportunities in the fight against neglected tropical diseases: a decade from the London Declaration on NTDs'.

serosim: An R package for simulating serological data arising from vaccination, epidemiological and antibody kinetics processes

serosim is an open-source R package designed to aid inference from serological studies, by simulating data arising from user-specified vaccine and antibody kinetics processes using a random effects model. Serological data are used to assess population immunity by directly measuring individuals' antibody titers. They uncover locations and/or populations which are susceptible and provide evidence of past infection or vaccination to help inform public health measures and surveillance. Both serological data and new analytical techniques used to interpret them are increasingly widespread. This creates a need for tools to simulate serological studies and the processes underlying observed titer values, as this will enable researchers to identify best practices for serological study design, and provide a standardized framework to evaluate the performance of different inference methods. serosim allows users to specify and adjust model inputs representing underlying processes responsible for generating the observed titer values like time-varying patterns of infection and vaccination, population demography, immunity and antibody kinetics, and serological sampling design in order to best represent the population and disease system(s) of interest. This package will be useful for planning sampling design of future serological studies, understanding determinants of observed serological data, and validating the accuracy and power of new statistical methods.

Navigating drug repurposing for Chagas disease: advances, challenges, and opportunities

Chagas disease is a vector-borne illness caused by the protozoan parasite Trypanosoma cruzi (T. cruzi). It poses a significant public health burden, particularly in the poorest regions of Latin America. Currently, there is no available vaccine, and chemotherapy has been the traditional treatment for Chagas disease. However, the treatment options are limited to just two outdated medicines, nifurtimox and benznidazole, which have serious side effects and low efficacy, especially during the chronic phase of the disease. Collectively, this has led the World Health Organization to classify it as a neglected disease. To address this problem, new drug regimens are urgently needed. Drug repurposing, which involves the use of existing drugs already approved for the treatment of other diseases, represents an increasingly important option. This approach offers potential cost reduction in new drug discovery processes and can address pharmaceutical bottlenecks in the development of drugs for Chagas disease. In this review, we discuss the state-of-the-art of drug repurposing approaches, including combination therapy with existing drugs, to overcome the formidable challenges associated with treating Chagas disease. Organized by original therapeutic area, we describe significant recent advances, as well as the challenges in this field. In particular, we identify candidates that exhibit potential for heightened efficacy and reduced toxicity profiles with the ultimate objective of accelerating the development of new, safe, and effective treatments for Chagas disease.

Temporal assessment of entomological surveillance of Trypanosoma cruzi vectors in an endemic area of northeastern Brazil

Entomological surveillance is essential for the control of triatomines and the prevention of Trypanosoma cruzi infection in humans and domestic animals. Thus, the objective of this study was to evaluate entomological indicators and triatomine control during the period from 2005 to 2015 in an endemic area in the state of Rio Grande do Norte, Brazil. This observational and retrospective study was developed based on data analysis related to active entomological surveillance activities and chemical control of infested housing units (HU) in the Agreste mesoregion of the state of Rio Grande do Norte, Brazil, in the period between 2005 to 2015. The quantitative analysis of housing units surveyed for entomological indicators was performed by linear regression of random effects (p < 0.05). The effect of the number of HU surveyed on the entomological indicators was analyzed by fitting a linear random effects regression model and an increasing intradomiciliary colonization rate was significant. In the period evaluated 92,156 housing units were investigated and the presence of triatomines was reported in 4,639 (5.0%). A total of 4,653 specimens of triatomines were captured and the species recorded were Triatoma pseudomaculata (n = 1,775), Triatoma brasiliensis (n = 1,569), Rhodnius nasutus (n = 741) and Panstrongylus lutzi (n = 568), with an index of natural infection by T. cruzi of 2.2%. Only 53.1% of the infested HU were subjected to chemical control. Moreover, there was a decrease in the total number of HU surveyed over time associated with an increase in the index of intradomiciliary colonization (p = 0.004). These data demonstrated that entomological surveillance and control of vectors in the Agreste mesoregion of the state has been discontinued, emphasizing the need for more effective public policies to effectively control the vectors, in order to avoid the exposure of humans and domestic animals to the risk of T. cruzi infection.

Health conditions of Hitnü indigenous people potentially exposed to crude oil in Arauca, Colombia

Introduction: The Hitnü indigenous people live in precarious sanitary conditions, with food insecurity and being victims of sociopolitical violence in Arauca, Colombia. In addition, it is possible that they may be affected by exposure to hydrocarbons found in oil. Objective: To identify the health outcomes of morbidity and mortality profiles of the Hitnü people that could be associated with the exposure to crude oil. Materials and methods: A cross-sectional study was carried out with Hitnü indigenous people, during February and March, 2021, time of drought. A household questionnaire was applied, and one individual to collect data from the environment around the house, occupations and other activities, as well as data from sociodemographic, signs, symptoms, and findings of a medical examination. The potential association with hydrocarbons was explored considering three groups: inhabitants in Arauca city, Aspejaná reserve (not exposed), and San José del Lipa and La Vorágine reserves (exposed by the Ele river and tributaries). With free listings, causes of death were explored. The study incorporated a rigorous intercultural management in all its components. Results: A total of 576 indigenous people from 16 settlements participated. The water consumed could serve as means of exposure to hydrocarbons. Health problems were very varied, including infectious and chronic diseases, malnutrition, and trauma. The masses on the neck were associated with residing in the ancestral reserves (PR = 3.86; CI95% 1.77-8.39), territories with potential exposure to crude-oil. The most relevant causes of death were homicide, tumors, and tuberculosis. Conclusion: For its possible association with exposure to hydrocarbons, it is a priority to start the intercultural study of lymphadenopathies in indigenous communities potentially exposed to crude oil.

Genetic Instability among Hitnü People Living in Colombian Crude-Oil Exploitation Areas

Oil exploitation, drilling, transportation, and processing in refineries produces a complex mixture of chemical compounds, including polycyclic aromatic hydrocarbons (PAHs), which may affect the health of populations living in the zone of influence of mining activities (PZOI). Thus, to better understand the effects of oil exploitation activities on cytogenetic endpoint frequency, we conducted a biomonitoring study in the Hitnü indigenous populations from eastern Colombia by using the cytokinesis micronucleus cytome assay (CBMN-cyt). PAH exposure was also measured by determine urine 1-hydroxypyrene (1-OHP) using HPLC. We also evaluated the relationship between DNA damage and 1-OHP levels in the oil exploitation area, as well as the modulating effects of community health factors, such as Chagas infection; nutritional status; and consumption of traditional hallucinogens, tobacco, and wine from traditional palms. The frequencies of the CBMN-cyt assay parameters were comparable between PZOI and Hitnü populations outside the zone of influence of mining activities (POZOI); however, a non-significant incremental trend among individuals from the PZOI for most of the DNA damage parameters was also observed. In agreement with these observations, levels of 1-OHP were also identified as a risk factor for increased MN frequency (PR = 1.20) compared to POZOI (PR = 0.7). Proximity to oil exploitation areas also constituted a risk factor for elevated frequencies of nucleoplasmic bridges (NPBs) and APOP-type cell death. Our results suggest that genetic instability and its potential effects among Hitnü individuals from PZOI and POZOI could be modulated by the combination of multiple factors, including the levels of 1-OHP in urine, malnutrition, and some traditional consumption practices.

Linear and Machine Learning modelling for spatiotemporal disease predictions: Force-of-Infection of Chagas disease

Background

Chagas disease is a long-lasting disease with a prolonged asymptomatic period. Cumulative indices of infection such as prevalence do not shed light on the current epidemiological situation, as they integrate infection over long periods. Instead, metrics such as the Force-of-Infection (FoI) provide information about the rate at which susceptible people become infected and permit sharper inference about temporal changes in infection rates. FoI is estimated by fitting (catalytic) models to available age-stratified serological (ground-truth) data. Predictive FoI modelling frameworks are then used to understand spatial and temporal trends indicative of heterogeneity in transmission and changes effected by control interventions. Ideally, these frameworks should be able to propagate uncertainty and handle spatiotemporal issues.

Methodology/principal findings

We compare three methods in their ability to propagate uncertainty and provide reliable estimates of FoI for Chagas disease in Colombia as a case study: two Machine Learning (ML) methods (Boosted Regression Trees (BRT) and Random Forest (RF)), and a Linear Model (LM) framework that we had developed previously. Our analyses show consistent results between the three modelling methods under scrutiny. The predictors (explanatory variables) selected, as well as the location of the most uncertain FoI values, were coherent across frameworks. RF was faster than BRT and LM, and provided estimates with fewer extreme values when extrapolating to areas where no ground-truth data were available. However, BRT and RF were less efficient at propagating uncertainty.

Conclusions/significance

The choice of FoI predictive models will depend on the objectives of the analysis. ML methods will help characterise the mean behaviour of the estimates, while LM will provide insight into the uncertainty surrounding such estimates. Our approach can be extended to the modelling of FoI patterns in other Chagas disease-endemic countries and to other infectious diseases for which serosurveys are regularly conducted for surveillance.

Metrics such as the per susceptible rate of infection acquisition (Force-of-Infection) are crucial to understand the current epidemiological situation and the impact of control interventions for long-lasting diseases in which the infection event might have occurred many years previously, such as Chagas disease. FoI values are estimated from serological age profiles, often obtained in a few locations. However, when using predictive models to estimate the FoI over time and space (including areas where serosurveys had not been conducted), methods able to handle and propagate uncertainty must be implemented; otherwise, overconfident predictions may be obtained. Although Machine Learning (ML) methods are powerful tools, they may not be able to entirely handle this challenge. Therefore, the use of ML must be considered in relation to the aims of the analyses. ML will be more relevant to characterise the central trends of the estimates while Linear Models will help identify areas where further serosurveys should be conducted to improve the reliability of the predictions. Our approaches can be used to generate FoI predictions in other Chagas disease-endemic countries as well as in other diseases for which serological surveillance data are collected.

Updated Estimates and Mapping for Prevalence of Chagas Disease among Adults, United States

Geographic scale estimates of disease in older Latin America–born US residents may be useful for prevention and early recognition of chronic sequelae.

We combined American Community Survey data with age-specific Trypanosoma cruzi prevalence derived from US surveys and World Health Organization reports to yield estimates of Chagas disease in the United States, which we mapped at the local level. In addition, we used blood donor data to estimate the relative prevalence of autochthonous T. cruzi infection. Our estimates indicate that 288,000 infected persons, including 57,000 Chagas cardiomyopathy patients and 43,000 infected reproductive-age women, currently live in the United States; 22–108 congenital infections occur annually. We estimated ≈10,000 prevalent cases of locally acquired T. cruzi infection. Mapping shows marked geographic heterogeneity of T. cruzi prevalence and illness. Reliable demographic and geographic data are key to guiding prevention and management of Chagas disease. Population-based surveys in high prevalence areas could improve the evidence base for future estimates. Knowledge of the demographics and geographic distribution of affected persons may aid practitioners in recognizing Chagas disease.

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.

The potential risk of enzootic Trypanosoma cruzi transmission inside four training and re-training military battalions (BITER) in Colombia

BACKGROUND

Colombia's National Army is one of the largest military institutions in the country based on the number of serving members and its presence throughout the country. There have been reports of cases of acute or chronic cases of Chagas disease among active military personnel. These may be the result of military-associated activities performed in jungles and other endemic areas or the consequence of exposure to Trypanosoma cruzi inside military establishments/facilities located in endemic areas. The aim of the present study was to describe the circulation of T. cruzi inside facilities housing four training and re-training battalions [Battalions of Instruction, Training en Re-training (BITERs)] located in municipalities with historical reports of triatomine bugs and Chagas disease cases. An entomological and faunal survey of domestic and sylvatic environments was conducted inside each of these military facilities.

METHODS

Infection in working and stray dogs present in each BITER location was determined using serological and molecular tools, and T. cruzi in mammal and triatomine bug samples was determined by PCR assay. The PCR products of the vertebrate 12S rRNA gene were also obtained and subjected to Sanger sequencing to identify blood-feeding sources. Finally, we performed a geospatial analysis to evaluate the coexistence of infected triatomines and mammals with the military personal inside of each BITER installation.

RESULTS

In total, 86 specimens were collected: 82 Rhodnius pallescens, two Rhodnius prolixus, one Triatoma dimidiata and one Triatoma maculata. The overall T. cruzi infection rate for R. pallescens and R. prolixus was 56.1 and 100% respectively, while T. dimidiata and T. maculata were not infected. Eight feeding sources were found for the infected triatomines, with opossum and humans being the most frequent sources of feeding (85.7%). Infection was most common in the common opossum Didelphis marsupialis, with infection levels of 77.7%. Sylvatic TcI was the most frequent genotype, found in 80% of triatomines and 75% of D. marsupialis. Of the samples collected from dogs (n = 52), five (9.6%; 95% confidence interval: 3.20-21.03) were seropositive based on two independent tests. Four of these dogs were creole and one was a working dog. The spatial analysis revealed a sympatry between infected vectors and mammals with the military population.

CONCLUSIONS

We have shown a potential risk of spillover of sylvatic T. cruzi transmission to humans by oral and vectorial transmission in two BITER installations in Colombia. The results indicate that installations where 100,000 active military personnel carry out training activities should be prioritized for epidemiological surveillance of Chagas disease.

Ecology, evolution, and epidemiology of zoonotic and vector-borne infectious diseases in French Guiana: Transdisciplinarity does matter to tackle new emerging threats

French Guiana is a European ultraperipheric region located on the northern Atlantic coast of South America. It constitutes an important forested region for biological conservation in the Neotropics. Although very sparsely populated, with its inhabitants mainly concentrated on the Atlantic coastal strip and along the two main rivers, it is marked by the presence and development of old and new epidemic disease outbreaks, both research and health priorities. In this review paper, we synthetize 15 years of multidisciplinary and integrative research at the interface between wildlife, ecosystem modification, human activities and sociodemographic development, and human health. This study reveals a complex epidemiological landscape marked by important transitional changes, facilitated by increased interconnections between wildlife, land-use change and human occupation and activity, human and trade transportation, demography with substantial immigration, and identified vector and parasite pharmacological resistance. Among other French Guianese characteristics, we demonstrate herein the existence of more complex multi-host disease life cycles than previously described for several disease systems in Central and South America, which clearly indicates that today the greater promiscuity between wildlife and humans due to demographic and economic pressures may offer novel settings for microbes and their hosts to circulate and spread. French Guiana is a microcosm that crystallizes all the current global environmental, demographic and socioeconomic change conditions, which may favor the development of ancient and future infectious diseases.

Force-of-infection of Taenia solium porcine cysticercosis: a modelling analysis to assess global incidence and prevalence trends

The World Health Organization (WHO) called, in 2012, for a validated strategy towards Taenia solium taeniasis/cysticercosis control and elimination. Estimating pig force-of-infection (FoI, the average rate at which susceptible pigs become infected) across geographical settings will help understand local epidemiology and inform effective intervention design. Porcine cysticercosis (PCC) age-prevalence data (from 15 studies in Latin America, Africa and Asia) were identified through systematic review. Catalytic models were fitted to the data using Bayesian methods, incorporating uncertainty in diagnostic performance, to estimate rates of antibody seroconversion, viable metacestode acquisition, and seroreversion/infection loss. There was evidence of antibody seroreversion across 5 studies, and of infection loss in 6 studies measured by antigen or necropsy, indicating transient serological responses and natural resolution of infection. Concerted efforts should be made to collect robust data using improved diagnostics to better understand geographical heterogeneities in T. solium transmission to support post-2020 WHO targets.

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.

Complementary Paths to Chagas Disease Elimination: The Impact of Combining Vector Control With Etiological Treatment

Background

The World Health Organization’s 2020 goals for Chagas disease are (1) interrupting vector-borne intradomiciliary transmission and (2) having all infected people under care in endemic countries. Insecticide spraying has proved efficacious for reaching the first goal, but active transmission remains in several regions. For the second, treatment has mostly been restricted to recently infected patients, who comprise only a small proportion of all infected individuals.

Methods

We extended our previous dynamic transmission model to simulate a domestic Chagas disease transmission cycle and examined the effects of both vector control and etiological treatment on achieving the operational criterion proposed by the Pan American Health Organization for intradomiciliary, vectorial transmission interruption (ie, <2% seroprevalence in children <5 years of age).

Results

Depending on endemicity, an antivectorial intervention that decreases vector density by 90% annually would achieve the transmission interruption criterion in 2–3 years (low endemicity) to >30 years (high endemicity). When this strategy is combined with annual etiological treatment in 10% of the infected human population, the seroprevalence criterion would be achieved, respectively, in 1 and 11 years.

Conclusions

Combining highly effective vector control with etiological (trypanocidal) treatment in humans would substantially reduce time to transmission interruption as well as infection incidence and prevalence. However, the success of vector control may depend on prevailing vector species. It will be crucial to improve the coverage of screening programs, the performance of diagnostic tests, the proportion of people treated, and the efficacy of trypanocidal drugs. While screening and access can be incremented as part of strengthening the health systems response, improving diagnostics performance and drug efficacy will require further research.

Prevalence of Trypanosoma cruzi infection in active military population of The Colombian National Army gathered in five departments

Background

The National Army of Colombia is present in all of the national territory, focused in sylvatic zones where they are exposed continually to potential risk of transmission of Trypanosoma cruzi, the etiological agent of the Chagas disease. People of this study were active personal that were born and lived during their first years in endemic areas of transmission through domiciled vectors as Rhodnius prolixus.

Aim

The main aim of this study was to estimate the prevalence of Chagas disease in the active military population of the National Army, gathered in five departments.

Methods

An observational and descriptive study with cross-sectional analysis was carried out. Blood sample each patient in order to apply serological diagnosis by two different Enzyme Linked ImmunoSorbent Assay tests, following the algorithm of National Institute of Health, Colombia. In cases of serum results with inconsistencies, a Hemagglutination Inhibition test and Indirect Immunofluorescence assay test were performed to solve inconclusiveness. Positive samples by two different tests were considered seropositive. Additionally, to each positive sample by at least one serological test, we did extraction of DNA for molecular diagnosis.

Results

295 serums were analyzed and two of them were positive in order to get a prevalence of 0.68%. Two samples analyzed by molecular diagnosis were negative.

Conclusion

The prevalence was < 1% It is probable the infection in the seropositive individuals occurred before enlisting in the military service due to origin locations with transmission such as Casanare and Boyacá. These findings allow defining the prevention and control programs of chronic cases and reduction in the disease burden.

Force of infection of Middle East respiratory syndrome in dromedary camels in Kenya

Middle East respiratory syndrome coronavirus (MERS-CoV) is a zoonotic disease transmitted from dromedary camels to people, which can result in outbreaks with human-to-human transmission. Because it is a subclinical infection in camels, epidemiological measures other than prevalence are challenging to assess. This study estimated the force of infection (FOI) of MERS-CoV in camel populations from age-stratified serological data. A cross-sectional study of MERS-CoV was conducted in Kenya from July 2016 to July 2017. Seroprevalence was stratified into four age groups: <1, 1–2, 2–3 and >3 years old. Age-independent and age-dependent linear and quadratic generalised linear models were used to estimate FOI in pastoral and ranching camel herds. Models were compared based on computed AIC values. Among pastoral herds, the age-dependent quadratic FOI was the best fit model, while the age-independent FOI was the best fit for the ranching herd data. FOI provides an indirect estimate of infection risk, which is especially valuable where direct estimates of incidence and other measures of infection are challenging to obtain. The FOIs estimated in this study provide important insight about MERS-CoV dynamics in the reservoir species, and contribute to our understanding of the zoonotic risks of this important public health threat.

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.

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.

Venezuela's humanitarian crisis, resurgence of vector-borne diseases, and implications for spillover in the region

In the past 5-10 years, Venezuela has faced a severe economic crisis, precipitated by political instability and declining oil revenue. Public health provision has been affected particularly. In this Review, we assess the impact of Venezuela's health-care crisis on vector-borne diseases, and the spillover into neighbouring countries. Between 2000 and 2015, Venezuela witnessed a 359% increase in malaria cases, followed by a 71% increase in 2017 (411 586 cases) compared with 2016 (240 613). Neighbouring countries, such as Brazil, have reported an escalating trend of imported malaria cases from Venezuela, from 1538 in 2014 to 3129 in 2017. In Venezuela, active Chagas disease transmission has been reported, with seroprevalence in children (<10 years), estimated to be as high as 12·5% in one community tested (n=64). Dengue incidence increased by more than four times between 1990 and 2016. The estimated incidence of chikungunya during its epidemic peak is 6975 cases per 100 000 people and that of Zika virus is 2057 cases per 100 000 people. The re-emergence of many vector-borne diseases represents a public health crisis in Venezuela and has the possibility of severely undermining regional disease elimination efforts. National, regional, and global authorities must take action to address these worsening epidemics and prevent their expansion beyond Venezuelan borders.

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.

How Modelling Can Enhance the Analysis of Imperfect Epidemic Data

Mathematical models play an increasingly important role in our understanding of the transmission and control of infectious diseases. Here, we present concrete examples illustrating how mathematical models, paired with rigorous statistical methods, are used to parse data of different levels of detail and breadth and estimate key epidemiological parameters (e.g., transmission and its determinants, severity, impact of interventions, drivers of epidemic dynamics) even when these parameters are not directly measurable, when data are limited, and when the epidemic process is only partially observed. Finally, we assess the hurdles to be taken to increase availability and applicability of these approaches in an effort to ultimately enhance their public health impact.

Many data can be used to estimate the transmission potential of a pathogen, including descriptions of the transmission chains, human cluster sizes, sources of infection, and epidemic curves.

An important agenda in public health is understanding the impact of control methods. However, the dynamic nature of epidemics makes this task challenging. Models can disentangle the natural course of outbreaks from the effect of external factors.

In the absence of reliable surveillance data, models can reconstruct epidemic history by combining age-specific seroprevalence data with an understanding of the natural history of infection.

Mechanisms of immunity are hard to observe at an individual level, yet they affect population-level dynamics. Models can tease out such signatures.

Morbidity and mortality can be difficult to estimate when many infections are unobserved and severe infections are reported more often. Models can be used to correct for under-reporting and selection bias.

Age trends in asymptomatic and symptomatic Leishmania donovani infection in the Indian subcontinent: A review and analysis of data from diagnostic and epidemiological studies

BACKGROUND

Age patterns in asymptomatic and symptomatic infection with Leishmania donovani, the causative agent of visceral leishmaniasis (VL) in the Indian subcontinent (ISC), are currently poorly understood. Age-stratified serology and infection incidence have been used to assess transmission levels of other diseases, which suggests that they may also be of use for monitoring and targeting control programmes to achieve elimination of VL and should be included in VL transmission dynamic models. We therefore analysed available age-stratified data on both disease incidence and prevalence of immune markers with the aim of collating the currently available data, estimating rates of infection, and informing modelling and future data collection.

METHODOLOGY/PRINCIPAL FINDINGS

A systematic literature search yielded 13 infection prevalence and 7 VL incidence studies meeting the inclusion criteria. Statistical tests were performed to identify trends by age, and according to diagnostic cut-off. Simple reversible catalytic models with age-independent and age-dependent infection rates were fitted to the prevalence data to estimate infection and reversion rates, and to test different hypotheses about the origin of variation in these rates. Most of the studies showed an increase in infection prevalence with age: from ≲10% seroprevalence (<20% Leishmanin skin test (LST) positivity) for 0-10-year-olds to >10% seroprevalence (>20% LST-positivity) for 30-40-year-olds, but overall prevalence varied considerably between studies. VL incidence was lower amongst 0-5-year-olds than older age groups in most studies; most showing a peak in incidence between ages 5 and 20. The age-independent catalytic model provided the best overall fit to the infection prevalence data, but the estimated rates for the less parsimonious age-dependent model were much closer to estimates from longitudinal studies, suggesting that infection rates may increase with age.

CONCLUSIONS/SIGNIFICANCE

Age patterns in asymptomatic infection prevalence and VL incidence in the ISC vary considerably with geographical location and time period. The increase in infection prevalence with age and peaked age-VL-incidence distribution may be due to lower exposure to infectious sandfly bites in young children, but also suggest that acquired immunity to the parasite increases with age. However, poor standardisation of serological tests makes it difficult to compare data from different studies and draw firm conclusions about drivers of variation in observed age patterns.

Are the London Declaration's 2020 goals sufficient to control Chagas disease?: Modeling scenarios for the Yucatan Peninsula

BACKGROUND

The 2020 Sustainable Development goals call for 100% certified interruption or control of the three main forms of Chagas disease transmission in Latin America. However, how much will achieving these goals to varying degrees control Chagas disease; what is the potential impact of missing these goals and if they are achieved, what may be left?

METHODS

We developed a compartmental simulation model that represents the triatomine, human host, and non-human host populations and vector-borne, congenital, and transfusional T. cruzi transmission between them in the domestic and peridomestic settings to evaluate the impact of limiting transmission in a 2,000 person virtual village in Yucatan, Mexico.

RESULTS

Interruption of domestic vectorial transmission had the largest impact on T. cruzi transmission and prevalence in all populations. Most of the gains were achieved within the first few years. Controlling vectorial transmission resulted in a 46.1-83.0% relative reduction in the number of new acute Chagas cases for a 50-100% interruption in domestic vector-host contact. Only controlling congenital transmission led to a 2.4-8.1% (30-100% interruption) relative reduction in the total number of new acute cases and reducing only transfusional transmission led to a 0.1-0.3% (30-100% reduction). Stopping all three forms of transmission resulted in 0.5 total transmission events over five years (compared to 5.0 with no interruption); interrupting all forms by 30% resulted in 3.4 events over five years per 2,000 persons.

CONCLUSIONS

While reducing domestic vectorial, congenital, and transfusional transmission can successfully reduce transmission to humans (up to 82% in one year), achieving the 2020 goals would still result in 0.5 new acute cases per 2,000 over five years. Even if the goals are missed, major gains can be achieved within the first few years. Interrupting transmission should be combined with other efforts such as a vaccine or improved access to care, especially for the population of already infected individuals.