Vector control infestation is the main strategy for preventing Chagas disease. When vector control actions are carried out in a sustained and committed way over time, triatomines presence in houses is reduced and consequently, the risk of vector transmission decreased. However, in areas where the infestation is reduced, a paradox occurs as these areas lose surveillance priority and are visited less and less frequently, and their chemical treatments are postponed. This misconception produces a huge setback to achieve the main objective, which is the vectorial transmission interruption. For this reason, it is important to generate strategies that guarantee constant entomological surveillance, to control areas where a low domiciliary infestation allows T. infestans population return to infestation levels found before control actions. For CBD, entomological evaluation frequency is greater than three years and, at each visit, evaluation coverage is reduced due to political decisions that limit PPCHLR logistic and budget.
In this work, the impact of incorporating community participation in areas with a low domestic infestation that in general are neither focus of study nor priority to apply vector control actions is analysed. The low frequency with a vertical program cannot meet demand in areas where infestation risk is known to be low [5], causing the domestic vector persistence to continue and recovering populations among spraying cycles [6]. Incorporating participatory approaches against vector-borne diseases has been shown to be important for control program sustainability [8, 10, 11, 19, 20]. However, there is still debate regarding the limitations of incorporating community participation in house surveillance circuit due to T. infestans presence reported in houses where it is not present, as positive false.
Specifically, in La Rioja province, it is assumed that a house is positive only when PPCHLR technicians corroborate T. infestans presence in DU. The theoretical vector control model would be annual intervention by specialized technicians who evaluate and spray houses. In fact, this logistical capacity does not exist. Given the actual situation, advantages and disadvantages of maintaining only vertical PPCHLR interventions in low infestation areas are necessary to be re-evaluated.
In this work, using field data collected in the same year and without modelling on indirectly estimated variables, two intervention types were compared, showing that costs in relation to DU visited, evaluated, and sprayed were lowered with community participation. In addition, a greater proportion of DU evaluated in relation to those visited as well as greater surface were covered with community participation.
Other studies have analysed the cost-effectiveness of different interventions types with similar results obtained in this work, although with completely different approaches that do not allow a direct comparison with our data. For example, in Mexico, the cost to evaluate entomologically a domicile, detecting T. dimidiata, was US$70 for an infested house by carrying out an active search and only US$10 when householders were involved [21]. Also, in Santiago del Estero (Argentina) a very complete analysis was carried out using variables related to costs considering community intervention, estimating that costs were reduced in surveillance phase. Cost-effectiveness was also analysed in attack phase, where householders sprayed owns houses, although this situation created vector control quality problems in long term [10]. These latter results would not be comparable to our data since our focus is only on entomological surveillance and the spraying is only carried out by specialized personnel.
Despite methodological differences, there are many works showing a cost decrease when community collaborates in surveillance phase [8, 10, 11, 19, 20, 22]. In this work, we recommended that community intervention is only in surveillance phase to guarantee an early triatomines detection but the spraying function is always responsibility of personnel specifically trained for this task.
In order to control circuit function correctly, we proposed that householders inform about the T. infestans presence in their houses and notify to Municipality. The municipal referent verifies or not this species presence. If houses are T. infestans positive, personnel designated for this purpose spray them and surroundings. Although, in this particular context, our CRILAR medical entomology team participates in a social commitment, it is expected that this activity should be carried out routinely by health area staff or Chagas municipal referent implying that there would be no extra costs. In this way, technician work is optimized, focusing the spraying on positive houses already surveyed by sanitary agents, while, at the same time, reducing travel wage and fuel costs for the transfer of PPCHLR personnel to field. These economic resources would be designated to higher infestation areas without causing a triatomine increase in areas visited sporadically.
In addition to the cost reduction, T. infestans domestic infestation estimated with community participation allowed a spatially heterogeneous infestation detection in the north of La Rioja. These results coincide with those obtained in the south of La Rioja [4, 5, 11] and in other areas of Gran Chaco [23]. Within of La Rioja Province, T. infestans domestic infestation in CBD was lower than in Los Llanos riojanos (13.8 vs 21.4%) carried out with community participation [11]. In relation to infection risk, in CBD, triatomines did not show evidence of T. cruzi infection while in Los Llanos exist vectorial transmission risk of T. cruzi [5, 11].
Within CBD, southern zone presented the highest risk of infestation. Heterogeneity in the infestation risk could be associated to climatic conditions and peridomestic structures presence. Climatic conditions could explain differences in T. infestans infestation among zones due to southern zone presented higher temperature and lower humidity in relation to the other ones. These climatic conditions, especially the temperature, could allow an optimal growth of the species as was observed by other authors [23, 24, 25]. Another factor that could explain differential zonal differences was the presence of peridomestic structures due to those gave refuge and feeding sources for triatomines [26]. Supplementary data (Additional file 1: Table S1) showed that southern zone presented the highest peridomestic structure percentage (58%, χ²= 64.67, gl = 2, p < 0.0001). All these results showed that there are several factors that promote T. infestans presence, particularly in this zone.
To understand the set of variables associated with infestation in the area help in design of entomological surveillance implementation. An orderly and efficient entomological surveillance system is necessary in rural areas far from the capital, since otherwise the feasibility of maintaining a successful chemical control diminishes. Knowing variables involve in the infestation risk is useful to estimate the most appropriate and economic routes carried out so as not to stop covering areas with the greatest vector transmission risk [23], increasing coverage and cost-effectiveness of interventions [27].
This work allowed to verify that involving community in entomological surveillance reduced costs, covered a greater surface, covered a greater proportion of DU evaluated, encouraged early infestation detection and is the first step in stimulating control interventions. Furthermore, it promoted an active and positive attitude in local population in relation to Chagas disease prevention. However, for this strategy to be effective, municipalities should carry out sustained surveillance work and chemical control interventions to prevent T. infestans populations from recovering after an application interval. Therefore, these actions must continue to be encouraged and, in addition, the authorities must be committed to giving a quick and effective response to householder demands.