Chagas Disease: A Ten Year Study (2004-2014)

Ten years (2004–2014) of Chagas disease surveillance and vector control in Ecuador: successes and challenges

by

Leonardo Quinde-Calderón1, Paulina Rios-Quituizaca2, Luis Solorzano and Eric Dumonteil

Chagas disease, or American tripanosomiasis, is caused by the protozoan parasite Trypanosoma cruzi, which is transmitted through the faeces of hematophagous insects of the triatomine family. Following a short acute phase, infected patients enter an initially asymptomatic chronic phase. 30–40% then evolve into a symptomatic chronic phase, characterised by a Chagasic cardiomyopathy and/or digestive megasyndromes [1].

Chagas disease in a major public health in Latin America, where current estimates suggest a total of nearly 6 million cases [2]. It causes healthcare costs of $24 billion and a burden of 29 385 250 Disease Adjusted Life Years (DALYs) [3]. Despite this, it is a neglected disease, disproportionately affecting poor populations [4, 5]. In Ecuador, there are an estimated 100–200 000 cases and both the cardiac and the digestive forms of the chronic phase have been observed [6]. The seroprevalence of T. cruzi infection is highly variable among the provinces, ranging from <1 to 5–6%, with a national average of 0.7% [6-8]. In 1978, Chagas disease notification became mandatory in Ecuador, which also joined the intergovernmental Initiative of Andean Countries for Chagas Disease Control in 1997. The main vector species in Ecuador are Triatoma dimidiata and Rhodnius ecuadoriensis, and several additional species are considered secondary vectors, particulary in the Amazon region [9, 10]. T. dimidiata is present in most of the coastal region, but unconnected to populations from Colombia and hence considered an introduced species [9, 10]. Preliminary molecular analysis supports the possible introduction of T. dimidiata from Central America (Nicaragua, Honduras) in colonial times [11-13]. The elimination of T. dimidiata from Ecuador by residual insecticide spraying is thus an important goal of vector control activities [10]. R. ecuadoriensis has been found in diverse habitats, with different levels of domiciliation according to the region [14-18]. It is believed to be controllable by insecticide spraying as well. Since 2004, the Ministry of Public Health of Ecuador has formalised activities for the epidemiologic and entomologic surveillance of Chagas disease, as well as vector control activities, through the Instituto Nacional de Investigación en Salud Pública (INSPI, National Institute for Research in Public Health) and the Servicio Nacional de Control y Vigilancia de enfermedades transmitidas por vectores artrópodos (SNEM, National Service for the Control and Surveillance of Diseases Transmitted by Arthropods) [19]. These programmes are intended to follow recommendations from a technical consultation through PAHO/WHO [20]. The objective of this work was to analyse the records of Chagas disease entomological and epidemiological surveillance activities from the Ministry of Public Health, to obtain a description of the current situation in Ecuador and to evaluate the impact of vector control activities over the past 10 years (2004–2014). Such analyses of national programmes are valuable in assessing the efficacy of established policies and programmes and making adjustments when needed [21-27]. SAFETY, SECURITY, HEALTH IN ECUADOR – READ THIS BOOK

Discussion

We analysed the records of entomologic and epidemiologic surveillance of triatomines and Chagas disease cases from the Ministry of Public Health of Ecuador, to evaluate the current situation of Chagas disease in the country and the impact of vector control efforts over the past 10 years. (2004–2014). This type of analysis has been found to be highly valuable to assess programme effectiveness, as well as to provide cues to improvements in their implementation in several other countries [22]. For example, community participation proved very helpful in strengthening Chagas disease surveillance and control in Honduras [26]; while in Argentina [27]; in Guatemala [25] and in Cochabamba, Bolivia [23], among others, the efficacy of vector control activities has been confirmed.

Chagas disease surveillance and control programmes were implemented in Ecuador largely upon recommendation of an extensive consultation by PAHO/WHO, which summarised the situation in the early 2000, and made clear recommendations on the public health benefit of such programmes due to the high estimated burden of Chagas disease in the country [20]. This report identified the coastal region as well as the southern Andean valleys as high-risk regions that needed to be prioritised for Chagas disease surveillance and vector control, while the Amazon region was considered as intermediate risk and priority [20]. In response, the high-risk areas were the initial focus of surveillance activities, particularly for vector surveillance, although some limited work was done in provinces of the Amazon region. In fact, due to limited resources, both human and financial, there have been important variations in the geographic coverage of the surveillance activities, which focused on a variable number of provinces and parishes from year to year. Thus, a major limitation of the data analysed is that they do not correspond to a homogenous and systematic national coverage and may thus still present an incomplete picture of the distribution of Chagas disease in Ecuador. Also, because of limited follow-up after insecticide spraying (in most cases a single visit 1–12 months postintervention), so that vector surveillance and control could focus on new infested parishes, the data are somewhat biased towards a high infestation and tend to minimise the effect of insecticide spraying. Nonetheless, they provide highly valuable information on the current situation in at least parts of the country, some of which confirm previous estimates, while others are being challenged.

First, these data confirm the role of T. dimidiata and R. ecuadoriensis as primary vectors in the country, representing 98% of the vectors collected over the past 10 years. Infestation levels also remain significant in many parts of the country, strengthening the need for continued vector control activities. Second, there has been a marked increase in the number of registered cases, which likely reflect improvements in the epidemiologic surveillance system. However, the number of registered cases is still well below the estimated 100–200 000 cases [6, 20], and the difficulties in identifying more cases in recent years highlight the need for reinforced epidemiologic surveillance. In fact, previous studies have identified cases from almost all the provinces, with the notable exception of Chimborazo, Tungurahua, Cotopaxi and Carchi from the Andean region [20]. Thus, improvements in epidemiologic surveillance are still needed, and recent efforts at decentralising Chagas disease surveillance should help making diagnosis more readily available throughout the country.

Combining entomologic and epidemiologic data confirms the major Chagas disease risk areas, but still provides an incomplete picture of the distribution of the disease in Ecuador. Indeed, transmission is also very likely in most of parishes (and provinces) adjacent to those where it was reported, even though neither cases nor infestation have been reported to date. T. cruzi transmission was recently described in the province of Esmeralda in north-eastern Ecuador [30] and in Pastaza, in the Amazon region [31, 32]. Nonetheless, current data clearly indicate the existence of three major epidemiologic scenario for Chagas disease transmission in Ecuador [6, 20]. The western coastal region is a confirmed high-risk region [33], where T. dimidiata predominates, although R. ecuadoriensis is also present. About 36% of all cases originate from this region. The Amazon region, which was initially classified as of medium risk [20], appears as the main source of cases in the country (45% of cases) and should thus be considered a very high priority for surveillance and control [8]. Conversely, the southern highland valleys west of the Andes, previously classified as a high-risk area [20], only account for 18% of the cases, in spite of reports of frequent house infestation [17, 18] and a seroprevalence of 3.6% [7]. Further studies should confirm the possible epidemiological changes in the Amazon region, which may be associated with increasing deforestation [8].

Based on initial assessments [6, 20], vector control has been exclusively focused on the western coastal region and to a lesser extent, in the southern highland valleys. Importantly, to date, no vector control activities have taken place in the Amazon region, even though about half of the reported cases originate from this region. Our analysis confirms the significant efficacy of vector control activities over the past 10 years, in spite of their limitation and constraints, but highlights the need for sustained high coverage activities to ensure continued success. Indeed, the effect of insecticide spraying was significant only when infestation was monitored within a year postspraying, and it was lost when a longer time lag was considered. In fact, it seems clear that the proposed elimination of T. dimidiata from the coastal region will require a strong and concerted effort to replicate the results obtained in a few parishes to the entire region. Vector control in other regions also needs to be strengthened, not only in the southern highland valleys, but critically in the Amazon region as well. Control of R. ecuadoriensis with insecticide spraying in southern Ecuador has been met with mixed success [17, 34], possibly due to a rather intrusive behaviour. Similarly, limited house infestation has been observed in the Amazon region, but several opportunistic sylvatic vector species can invade houses to feed on humans, and will require alternative strategies to be implemented for their control [34, 35]. Combining information from entomological and epidemiological surveillance is also key to better identify risk areas. Finally, achieving sustainability over time and a wide geographic coverage of surveillance and control activities has been a challenge for many national programmes for Chagas disease control throughout Latin America, as it requires a strong political will and commitment [23, 27, 36].

In conclusion, the analysis of national epidemiologic and entomologic surveillance data confirmed the presence of at least three distinct Chagas disease transmission scenarios in Ecuador. Importantly, the Amazon region is emerging as a high priority area, where nearly half of T. cruzi infection cases originate. The coastal region and the southern highland valleys remain two of the historically important high-risk area, even though risk seems to have decreased in the later region. Vector control efforts over the past 10 years have been effective in the coastal region, where T. dimidiata predominates, but need to be sustained and expanded for the elimination of this vector to be feasible. Also, novel vector control interventions need to be designed to reduce intrusion by several triatomine species present in the Amazon region as well as in southern Ecuador. The successful control of Chagas disease in Ecuador will thus require strong political commitment to sustain current achievements and increase the national coverage of these programmes. Read Full Article