Home Economics American Trypanosomiasis Chagas Disease, Second Edition: One Hundred Years of Research
Criteria for stratification of vector control priorities
Often, the available resources for the vector control interventions do not allow the coverage of all the endemic areas. In these cases, some sort of prioritization is needed, and knowledge to build priorities under these circumstances has been accumulated from a number of operational research studies. Two cases, with different approaches, are presented below showing possibilities to carry out the interventions under tight budgets.
The first case is the control of Chagas disease vectors in Central America (CA) within the context of the Initiative of the Central American Countries (IPCA). Since establishment of the IPCA in 1997, Chagas disease vector control in Central America shifted in three dimensions: the main target from R. prolixus to T. dimidiata; operational phase from attack to surveillance; and management focus from impact to sustainability. From 2000, efforts to eliminate R. prolixus and to reduce T. dimidiata were intensified in Guatemala, El Salvador, Honduras, and Nicaragua. Vector control activities received assistance from several sources, particularly the Pan American Health Organization (PAHO), Japan International Cooperation Agency (JICA), NGOs, and local universities. Through this assistance, the Ministries of Health of the IPCA government obtained IRS equipment, insecticides, and vehicles, and developed management capacity to administer vector control and surveillance activities at the national and local levels through projects with JICA. The projects reinforced the communication between the National Programs and local health services, which had been debilitated during the process of decentralization of the health systems, and consequently improved the operational performance. As the vector control activities were scaled up, villages with R. prolixus were identified and treated by IRS. The number of villages identified with R. prolixus reached 317 in Guatemala during 2000—8, 228 in Honduras during 2003—10 and 9 in Nicaragua during 2002—13.18,48 As of February 2016, there have been no further reports of this vector species in Central America since the last finding in a village in Matagalpa in Nicaragua 2013. As a result of the coordinated effort the IPCA and PAHO certified Guatemala in 2008, Nicaragua and Honduras in 2011 for interruption of Chagas disease transmission by R. prolixus, and El Salvador in 2010 and Costa Rica in 2011 for elimination of the vector. Along with the advance in elimination of R. prolixus, indoor infestation rates with T. dimidiata have also declined from 14.5% in 2000 to 3.6% in 2012 in Guatemala, from 20.9% in 1999—2000 to 2.0% in 2012 in El Salvador, and from 21.9% in 2004 to 3.1% in 2012 in Honduras.19
As the vector infestation decreased substantially, the operational phase shifted from attack to surveillance and so did the management focus from impact to sustainability. Considering the need to sustain vector surveillance extensively and indefinitely in particular for T. dimidiata, a strategy had to be cost-effective and practical, that is, community-based and embedded in local health systems. To this end, Guatemala, El Salvador, Honduras, and Nicaragua installed Chagas disease vector surveillance mostly at the health facilities closest to the community. It was aimed to facilitate optimization of locally available resources and opportunities, efficient response to vector notification from the community and therefore efforts to sustain the surveillance systems. Having divided vector surveillance into five core components (1. health promotion, 2. vector detection, 3. vector notification, 4. data analysis and action planning, 5. response to vector notification), the activities became customizable, distributable, and sharable among different stakeholders, including physicians, nurses, operational technicians, community health volunteers, community sprayers, and the population.49,50 In Guatemala, while vector control specialists of departmental health offices continued promoting vector notification, analyzing data, and providing response for sporadic notifications, these tasks were delegated to municipal vector control teams in endemic areas. In El Salvador where a limited number of vector control specialists were stationed at the departmental health office, the surveillance tasks were shifted to health promotors of health centers who visit communities monthly or bimonthly. The departmental vector control specialists became trainers, supervisors, and supporters to provide technical assistance, maintain equipment, and supply materials. In Honduras, where operational functions were more decentralized and incorporated into primary health care, the surveillance responsibilities were assigned to the health centers in which activities are organized among clinical and operational staff, community heath volunteers, and community sprayers. In Nicaragua, the surveillance responsibilities were also assigned to the health centers, where the tasks are mostly carried out by the community family health team consisting of physicians, nurses, and auxiliary nurses during their regular visits and by vector control technicians during their occasional visits to communities. In addition to the surveillance models, response criteria varied slightly between countries. Although the countries agreed to spray all houses in villages infested with R. prolixus, for T. dimidiata Guatemala and Honduras responded with IRS only when nymphs or numerous adults were found inside houses as possible indication of colonization and for other vector notifications provided educational advice for house improvement. El Salvador applied IRS to all houses notified with nymphs or adults of T. dimidiata and all houses within a radius of 100 m where vector-borne Chagas transmission occurred. Nicaragua implemented a strategy to accumulate the vector notifications for 6 months and spray all houses in the village if more than 20% of houses were infested with T. dimidiata, spray all infested houses in villages with 5—20% of indoor infestation rates, and visit all infested houses where less than 5% of houses in the community notified the vector. Because of heterogeneous vector distribution, notification patterns, involved actors and response criteria between and within countries, monitoring of community-based surveillance focused on the number of houses found infested by vector notifications and the rate of infested houses with response. Despite the lack of statistical representativeness and standardized quality, these indicators were sufficient to approximate vector distributions and functionality of community-based surveillance, to take further actions such as entomological surveys, close monitoring, and specific training. Further, response to vector notification was the most important yet challenging task, in particular in resource limited settings, to minimize the infection risks and sustain the surveillance systems. The key to maintain a high response rate to vector notification was constant monitoring of surveillance systems by the departmental health office, regardless of the number of vector notifications, the number of operational technicians or community health volunteers, the degree of decentralization of response to vector report, interval between vector notification and response, and presence of aid agencies.51
Community-based surveillance once embedded in local health systems may be sustained with minimum resources and efforts, however, it can also relax and languish—potentially leading to unreported reinfestation of vectors. To reactivate surveillance activities, bug search campaigns were found to be effective. In the Department of Jalapa in Guatemala where R. prolixus had previously been found in 15 out of 64 villages but apparently absent since 2002, according to community- based vector surveillance, the departmental health office organized a Chagas bug hunting campaign in 2007 involving local health services, primary schools, NGOs, community health volunteers, media, and private companies. As a result, two villages were found infested with R. prolixus. The number of notifications of T. dimidiata also rose sharply from an annual average of 36 during 2004—2006 to 205 in 2007.52 Similar effects of such campaigns were found in the department of Intibuca in Honduras, where a bug hunting campaign involving schoolchildren, community health volunteers, and media led to discovery of a new village infested with R. prolixus in 2010. To augment the sensitivity of vector detection, the Central American countries have also investigated houses at risk of infestation and reinfestation in villages with a history of presence of R. prolixus and in areas previously endemic to T. dimidiata. However, countries are yet to implement systematic serological evaluation mechanisms, which could be facilitated by a regional policy and leadership, to analyze the disease transmission levels over time under community-based surveillance. Currently long-term consequence of surveillance is to be observed through seroprevalence of screening at blood banks.
The second case refers to vector control activities in La Rioja province (Argentina)—historically highly endemic for Chagas disease with active vectorial transmission.53 From 2004, a new structure for the vector control program of the province was organized. The new vector control activities, besides the normal entomological evaluation and insecticide application, included the individual coding of rural houses and geolocation using a global positioning system device and the organization of a regularly maintained information system. After 6—12 months, the
vector control field teams returned to the previously reported intradomestic infested houses to carry out a new entomological evaluation and respray the houses (intra- and peridomestic application) if still infested. In parallel, using the geographic information collected in the field, a spatial analysis was carried out of house infestation to identify spatial aggregates, where the activities of the field teams could be reinforced. Using this simple strategy, with a modest number of personnel and field vehicles during 5 years of uninterrupted activities, the intradomestic infestation rates by T. infestans dropped from 25% to less than 1%, and no acute cases of Chagas disease were reported. Peridomestic infestation is still relatively high in some provincial departments (>20%), and continued efforts integrating other vector control methods (e.g., modification of peridomestic structures for animal shelters) are currently under way in the affected areas.9,34,35,47
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