Chagas disease vector control in Central America

As the Southern Cone Initiative proceeds steadily towards eradication of Triatoma infestans, there is increasing interest in applying similar approaches to control Chagas disease vectors in Mexico, Central America and countries of the Andean Pact. Here, Chris Schofield and Jean-Pierre Dujardin discuss the technical feasibility of such an approach.     

The potential economic value of a Trypanosoma cruzi (Chagas disease) vaccine in Latin America

Background

Chagas disease, caused by the parasite Trypanosoma cruzi (T. cruzi), is the leading etiology of non-ischemic heart disease worldwide, with Latin America bearing the majority of the burden. This substantial burden and the limitations of current interventions have motivated efforts to develop a vaccine against T. cruzi.

Methodology/Principal Findings

We constructed a decision analytic Markov computer simulation model to assess the potential economic value of a T. cruzi vaccine in Latin America from the societal perspective. Each simulation run calculated the incremental cost-effectiveness ratio (ICER), or the cost per disability-adjusted life year (DALY) avoided, of vaccination. Sensitivity analyses evaluated the impact of varying key model parameters such as vaccine cost (range: $0.50–$200), vaccine efficacy (range: 25%–75%), the cost of acute-phase drug treatment (range: $10–$150 to account for variations in acute-phase treatment regimens), and risk of infection (range: 1%–20%). Additional analyses determined the incremental cost of vaccinating an individual and the cost per averted congestive heart failure case. Vaccination was considered highly cost-effective when the ICER was ≤1 times the GDP/capita, still cost-effective when the ICER was between 1 and 3 times the GDP/capita, and not cost-effective when the ICER was >3 times the GDP/capita. Our results showed vaccination to be very cost-effective and often economically dominant (i.e., saving costs as well providing health benefits) for a wide range of scenarios, e.g., even when risk of infection was as low as 1% and vaccine efficacy was as low as 25%. Vaccinating an individual could likely provide net cost savings that rise substantially as risk of infection or vaccine efficacy increase.

Conclusions/Significance

Results indicate that a T. cruzi vaccine could provide substantial economic benefit, depending on the cost of the vaccine, and support continued efforts to develop a human vaccine.     

Chagas infection transmission control: situation of transfusional transmission in Brazil and other countries of Latin America

The transmission of the transfusion-associated Chagas disease is an important mechanism of its dissemination in several Latin American countries. The transmission risk depends on five factors: prevalence of infection in blood donors, degree of serological coverage, sensibility of used tests, safety of obtained results and infection risk. The Southern Cone Iniciative set off by the Pan-American Health Organization, in 1991, is contributing to the implementation of blood law in each endemic country, and to reduce the risk of transfusional transmission of this horrible disease. Despite the clear improvement of Brasilian hemotherapy after 1980 (with the creation of the Blood National Program - Pró-Sangue) and the significant reduction of the chagasic infection among its blood donors; socio-economic, politic and cultural unlevels, prevent it from reaching the necessary universality and security. In order to assure both, the Brazilian Ministry of Health decided to restructure its blood system. In May, 1998, a great program was launched, to reach a specific goal: Blood - 100% with quality safety in all its process until 2003. It was divided in 12 projects, intends to guarantee the quality and self sufficiency in blood and hemoderivates.     

The future of Chagas disease control

In the past 15 years, there have been major advances in the control of Chagas disease in most of the countries endemic for this infection. Attention now turns to the future continuity of surveillance and control interventions - especially in regions where control has been so successful that the epidemiological significance of Chagas disease is in steep decline. The effort and expenditure of the recent past cannot continue indefinitely, but a degree of surveillance and selective intervention will be required because of the risk of new infestations and infections resulting from adventitious silvatic vectors accidentally entering houses. In this review, we summarize the progress of multinational control initiatives against Chagas disease. In addition, we suggest that the most sustainable approach to future surveillance involves both the primary healthcare system and university-based teams, with progressively greater attention given to case detection and treatment. Such an idea is not new, but we believe that it merits extensive discussion because of the different ways that research and health interventions are financed and because of the need to establish clearer reporting links between the research communities and the national health authorities.     

The neglected tropical diseases of Latin America and the Caribbean: a review of disease burden and distribution and a roadmap for control and elimination

The neglected tropical diseases (NTDs) represent some of the most common infections of the poorest people living in the Latin American and Caribbean region (LAC). Because they primarily afflict the disenfranchised poor as well as selected indigenous populations and people of African descent, the NTDs in LAC are largely forgotten diseases even though their collective disease burden may exceed better known conditions such as of HIV/AIDS, tuberculosis, or malaria. Based on their prevalence and healthy life years lost from disability, hookworm infection, other soil-transmitted helminth infections, and Chagas disease are the most important NTDs in LAC, followed by dengue, schistosomiasis, leishmaniasis, trachoma, leprosy, and lymphatic filariasis. On the other hand, for some important NTDs, such as leptospirosis and cysticercosis, complete disease burden estimates are not available. The NTDs in LAC geographically concentrate in 11 different sub-regions, each with a distinctive human and environmental ecology. In the coming years, schistosomiasis could be eliminated in the Caribbean and transmission of lymphatic filariasis and onchocerciasis could be eliminated in Latin America. However, the highest disease burden NTDs, such as Chagas disease, soil-transmitted helminth infections, and hookworm and schistosomiasis co-infections, may first require scale-up of existing resources or the development of new control tools in order to achieve control or elimination. Ultimately, the roadmap for the control and elimination of the more widespread NTDs will require an inter-sectoral approach that bridges public health, social services, and environmental interventions.     

Ecological and physiological thermal niches to understand distribution of Chagas disease vectors in Latin America

In order to assess how triatomines (Hemiptera, Reduviidae), Chagas disease vectors, are distributed through Latin America, we analysed the relationship between the ecological niche and the limits of the physiological thermal niche in seven species of triatomines. We combined two methodological approaches: species distribution models, and physiological tolerances. First, we modelled the ecological niche and identified the most important abiotic factor for their distribution. Then, thermal tolerance limits were analysed by measuring maximum and minimum critical temperatures, upper lethal temperature, and ‘chill‐coma recovery time’. Finally, we used phylogenetic independent contrasts to analyse the link between limiting factors and the thermal tolerance range for the assessment of ecological hypotheses that provide a different outlook for the geo‐epidemiology of Chagas disease. In triatomines, thermo‐tolerance range increases with increasing latitude mainly due to better cold tolerances, suggesting an effect of thermal selection. In turn, physiological analyses show that species reaching southernmost areas have a higher thermo‐tolerance than those with tropical distributions, denoting that thermo‐tolerance is limiting the southern distribution. Understanding the latitudinal range along its physiological limits of disease vectors may prove useful to test ecological hypotheses and improve strategies and efficiency of vector control at the local and regional levels.     

Current situation of Chagas disease in Central America

Chagas disease in Central America is known since 1913 when the first human case was reported in El Salvador. The other Central American countries reported their first cases between 1933 and 1967. On October 1997 was launched the Central American Initiative for Chagas Disease Control (IPCA). The objectives of this sub-regional Initiative are: (1) the elimination of Rhodnius prolixus in Central America; (2) the reduction of the domiciliary infestation of Triatoma dimidiata; and (3) the elimination of the transfusion transmission of Trypanosoma cruzi. Significant advancements being close to the elimination of R. prolixus in Central America and the control of the transfusion transmission has been a transcendent achievement for the sub-region. The main challenges that the IPCA will have in the close future are: developing effective strategies for control and surveillance of T. dimidiata; and surveillance of other emerging triatominae species like R. pallescens, T. nitida, and T. ryckmani.     

Augmentative biological control of arthropods in Latin America

Augmentative forms of biological control, wherenatural enemies are periodically introduced,are applied over large areas in variouscropping systems in Latin America. About 25%of the world area under augmentative control issituated in this region. Well-known examplesare the use of species of the egg parasitoidTrichogramma for management ofLepidoptera in various crops. In Mexico, forexample, about 1.5 million hectares are treatedwith Trichogramma spp. Application ofTrichogramma also occurs on large areasin Colombia and Cuba, but use is limited inother Latin American countries for economicreasons, the generally low level of educationof farmers, and, more importantly, because ofthe intensive use of pesticides that preventsuse of natural enemies. Of the other eggparasitoids, the main species used incommercial releases are Trissolcusbasalis (Wollaston) against the heteropteranNezara viridula (L.) in soybean inBrazil, and Telenomus remus Nixon againstSpodoptera frugiperda (J.E. Smith) incorn in Venezuela. Natural enemies attackinglarval and pupal stages are not used to a largeextent in augmentative biological control infield crops, with the exception of the use ofCotesia parasitoids against sugarcaneborers in Brazil and several other LatinAmerican countries. In addition to the use ofparasitoids and predators, Latin America isapplying microbial control agents on a largescale, such as viruses for control ofcaterpillars in soybean, fungi for control ofpests in coffee, cotton and sugar cane, andnematodes for control of soil pests. A recentdevelopment in biological control in LatinAmerica is the use of natural enemies andantagonists for disease and pest control inprotected cultivation, for example, inColombia, Brazil and Peru. Up to date, reliablefigures on current use of inundative andseasonal inoculative biological controlappeared hard to obtain, but it is clear thatLatin America currently is a main player in thefield of augmentative releases.     

Update on Chagas disease in Venezuela--a review

The present article reviews the status of Chagas disease in Venezuela based on the detection of Trypanosoma cruzi infections both in referred patients with clinical presumptive diagnosis (1988-2002) and in individuals sampled from rural localities representative of the different geographical regions of the country (1995-2002). In the former group from 306 individuals examined, 174 (56.8%) were seropositive to T. cruzi; 73 (42%) in the acute phase with 52 (71%) showing blood circulating parasites, and from these 38% were children under 10 years old. The other 101 (58%) showed chronic infection at different degrees of cardiac complication. In addition, serologic examination of 3835 individuals from rural areas revealed 11.7% seroprevalence. From these, 8.5% (38/448) were children aged from 0 to 10 years old. These figures suggest that Chagas disease may be re-emerging in Venezuela judging for the active transmission detected during the last decade. The success of the Venezuelan anti-chagasic campaign during the last 40 years is evaluated in the frame of the present results. The epidemiological situation is discussed and recommendation to consider Chagas disease as a national priority is given.     

Chagas disease screening in pregnant Latin American women: Adherence to a systematic screening protocol in a non-endemic country

BackgroundChagas disease (CD) is a chronic parasitic disease caused by Trypanosoma cruzi and is endemic to continental Latin America. In Spain, the main transmission route is congenital. We aimed to assess adherence to regional recommendations of universal screening for CD during pregnancy in Latin American women in the province of Alicante from 2014 to 2018.Methodology/Principal findingsRetrospective quality study using two data sources: 1) delivery records of Latin American women that gave birth in the 10 public hospitals of Alicante between January 2014 and December 2018; and 2) records of Chagas serologies carried out in those centers between May 2013 and December 2018. There were 3026 deliveries in Latin American women during the study period; 1178 (38.9%) underwent CD serology. Screening adherence ranged from 17.2% to 59.3% in the different health departments and was higher in Bolivian women (48.3%). Twenty-six deliveries (2.2%) had a positive screening; CD was confirmed in 23 (2%) deliveries of 21 women. Bolivians had the highest seroprevalence (21/112; 18.7%), followed by Colombians (1/333; 0.3%) and Ecuadorians (1/348; 0.3%). Of 21 CD-positive women (19 Bolivians, 1 Colombian, 1 Ecuadorian), infection was already known in 12 (57.1%), and 9 (42.9%) had already been treated. Only 1 of the 12 untreated women (8.3%) was treated postpartum. Follow-up started in 20 of the 23 (87.0%) neonates but was completed only in 11 (47.8%); no cases of congenital transmission were detected. Among the 1848 unscreened deliveries, we estimate 43 undiagnosed cases of CD and 1 to 2 undetected cases of congenital transmission.Conclusions/SignificanceAdherence to recommendations of systematic screening for CD in Latin American pregnant women in Alicante can be improved. Strategies to strengthen treatment of postpartum women and monitoring of exposed newborns are needed. Currently, there may be undetected cases of congenital transmission in our province.     

Community participation in Chagas disease vector surveillance: systematic review

Background

Vector control has substantially reduced Chagas disease (ChD) incidence. However, transmission by household-reinfesting triatomines persists, suggesting that entomological surveillance should play a crucial role in the long-term interruption of transmission. Yet, infestation foci become smaller and harder to detect as vector control proceeds, and highly sensitive surveillance methods are needed. Community participation (CP) and vector-detection devices (VDDs) are both thought to enhance surveillance, but this remains to be thoroughly assessed.

Methodology/Principal Findings

We searched Medline, Web of Knowledge, Scopus, LILACS, SciELO, the bibliographies of retrieved studies, and our own records. Data from studies describing vector control and/or surveillance interventions were extracted by two reviewers. Outcomes of primary interest included changes in infestation rates and the detection of infestation/reinfestation foci. Most results likely depended on study- and site-specific conditions, precluding meta-analysis, but we re-analysed data from studies comparing vector control and detection methods whenever possible. Results confirm that professional, insecticide-based vector control is highly effective, but also show that reinfestation by native triatomines is common and widespread across Latin America. Bug notification by householders (the simplest CP-based strategy) significantly boosts vector detection probabilities; in comparison, both active searches and VDDs perform poorly, although they might in some cases complement each other.

Conclusions/Significance

CP should become a strategic component of ChD surveillance, but only professional insecticide spraying seems consistently effective at eliminating infestation foci. Involvement of stakeholders at all process stages, from planning to evaluation, would probably enhance such CP-based strategies.     

The one-person household in Latin America: a brief note.

Drawing from World Fertility Survey and UN Demographic Yearbook data, this short paper considers the prevalence and composition of 1-person households in selected countries of the world, with particular attention to Latin America and the United States. In descending order of prevalence, 1-person households are most prevalent in Western culture group countries, Southern and Eastern Europe, sub-Saharan Africa, Latin America, Asia, and the Middle East. The proportion of these households is in fact growing in both the U.S. and Europe, and is associated with a growing proportion of elderly in the population, and a growing tendency among young adults to leave their parents' homes before marriage. Accordingly, most 1-person households are comprised of those young and never-married, and old and formerly-married. Debate remains over whether this trend is primarily influenced by growing affluence or changing ideas. This pattern contrasts sharply with that observed in Latin America. There, a majority of elderly live in extended households, most youths reside at parents' home until marriage, and many middle-age adults live alone. This latter phenomenon may result from comparatively higher levels of marital disruption and migration. A larger proportion of 1-person householders are therefore outside of the 2 aforementioned majority groups observed in the U.S. In closing, the paper again observes the difference between the 2 patterns, yet fails to speculate upon whether the Latin American pattern will grow to resemble that found in the U.S. and Europe.     

The impact and control of biofouling in marine aquaculture: a review

Biofouling in marine aquaculture is a specific problem where both the target culture species and/or infrastructure are exposed to a diverse array of fouling organisms, with significant production impacts. In shellfish aquaculture the key impact is the direct fouling of stock causing physical damage, mechanical interference, biological competition and environmental modification, while infrastructure is also impacted. In contrast, the key impact in finfish aquaculture is the fouling of infrastructure which restricts water exchange, increases disease risk and causes deformation of cages and structures. Consequently, the economic costs associated with biofouling control are substantial. Conservative estimates are consistently between 5-10% of production costs (equivalent to US$ 1.5 to 3 billion yr(-1)), illustrating the need for effective mitigation methods and technologies. The control of biofouling in aquaculture is achieved through the avoidance of natural recruitment, physical removal and the use of antifoulants. However, the continued rise and expansion of the aquaculture industry and the increasingly stringent legislation for biocides in food production necessitates the development of innovative antifouling strategies. These must meet environmental, societal, and economic benchmarks while effectively preventing the settlement and growth of resilient multi-species consortia of biofouling organisms.     

The impact and control of biofouling in marine aquaculture: a review

Biofouling in marine aquaculture is a specific problem where both the target culture species and/or infrastructure are exposed to a diverse array of fouling organisms, with significant production impacts. In shellfish aquaculture the key impact is the direct fouling of stock causing physical damage, mechanical interference, biological competition and environmental modification, while infrastructure is also impacted. In contrast, the key impact in finfish aquaculture is the fouling of infrastructure which restricts water exchange, increases disease risk and causes deformation of cages and structures. Consequently, the economic costs associated with biofouling control are substantial. Conservative estimates are consistently between 5–10% of production costs (equivalent to US$ 1.5 to 3 billion yr^?1), illustrating the need for effective mitigation methods and technologies. The control of biofouling in aquaculture is achieved through the avoidance of natural recruitment, physical removal and the use of antifoulants. However, the continued rise and expansion of the aquaculture industry and the increasingly stringent legislation for biocides in food production necessitates the development of innovative antifouling strategies. These must meet environmental, societal, and economic benchmarks while effectively preventing the settlement and growth of resilient multi-species consortia of biofouling organisms.     

Community cooperatives and insecticide-treated materials for malaria control: a new experience in Latin America

Background and objectives

Insecticide-treated materials (ITMs) are effective in substantially reducing the burden of malaria and other vector-borne diseases; but how can high coverage rates of ITMs be achieved and maintained? In south Mexico and on the Pacific and Atlantic coasts of Colombia 14 community-based cooperatives offering three different kinds of ITM services (sale of impregnation services; sale of impregnated nets; production of nets and sale of impregnated nets) were formed and supervised by a national health service (IMSS-SOLIDARIDAD, Mexico) and by an academic institution (the Colombian Institute of Tropical Medicine) along with local district health services. The objectives of this research were to analyse the processes and results of this approach and to identify the favourable and limiting factors.

Methods

The methods used for data collection and analysis were group discussions, individual and semi-structured interviews with users and non-users of ITMs, individual in-depth interviews with cooperative members and supervisors, checks of sales book and observation of impregnation services.

Results

Coverage with unimpregnated nets was above 50% in all study areas. The fastest increase of ITM coverage was achieved through the exclusive sale of impregnation services. Low-cost social marketing techniques were used to increase demand. The large-scale production of nets in two cooperatives was only possible with the aid of an international NGO which ordered impregnated bednets for their target group. A number of favourable and limiting factors relating to the success of ITM cooperatives were identified. Of particular importance for the more successful Mexican cooperatives were: a) support by health services, b) smaller size, c) lesser desire for quick returns and d) lower ITM unit costs.

Conclusions

ITM community cooperatives supported and supervised by the health services have good potential in the Latin American context for achieving and maintaining high impregnation rates.     

A critical review on Chagas disease chemotherapy

In this "Critical Review" we made a historical introduction of drugs assayed against Chagas disease beginning in 1912 with the works of Mayer and Rocha Lima up to the experimental use of nitrofurazone. In the beginning of the 70s, nifurtimox and benznidazole were introduced for clinical treatment, but results showed a great variability and there is still a controversy about their use for chronic cases. After the introduction of these nitroheterocycles only a few compounds were assayed in chagasic patients. The great advances in vector control in the South Cone countries, and the demonstration of parasite in chronic patients indicated the urgency to discuss the etiologic treatment during this phase, reinforcing the need to find drugs with more efficacy and less toxicity. We also review potential targets in the parasite and present a survey about new classes of synthetic and natural compounds studied after 1992/1993, with which we intend to give to the reader a general view about experimental studies in the area of the chemotherapy of Chagas disease, complementing the previous papers of Brener (1979) and De Castro (1993).     

Histoplasmosis: Epidemiology in Latin America

Histoplasmosis is a frequent health problem in Latin American countries, but the fact that it is not a reportable disease prevents reliable estimates of its real incidence and impact on public health. Epidemiologic and clinical data remain patchy in general, and in some countries the information available is very limited. Histoplasmosis has a significant public health impact in susceptible populations such as immunosuppressed individuals, in whom the disease is associated with poor outcomes. Limited availability of diagnostic tools in many regions of Latin America is an additional problem, as many patients are already severely ill by the time of the diagnosis. Efforts are therefore necessary to ensure early diagnosis and appropriate treatment, limit the severity of the disease manifestations, and reduce morbidity and mortality. This paper reviews important aspects of the epidemiology of histoplasmosis, the most clinically significant endemic mycosis in Latin America.