The control of T. infestans infestation is the main strategy for the prevention of Chagas disease in Argentina. 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 [12, 25]. This misconception produces a huge setback to achieve the main objective, which is the vectorial transmission interruption. 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.
Theoretical vertical vector control model would be annual intervention by specialized technicians who evaluate and spray houses . In fact, this logistical capacity does not exist in La Rioja province. 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, 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, 7], causing the domestic vector persistence to continue and recovering populations among spraying cycles [6, 26]. Incorporating participatory approaches against vector-borne diseases has been shown to be important for control program sustainability [9, 11, 13, 26, 27, 28, 29, 30]. Periodic inspection allows the early detection of new foci of reinfestation in the intradomicile [15, 17, 31]. Although, bio-eco-social approach not always reduce the infestation by itself . In addition, one of the main criticisms of the incorporation of community participation in health programs refers to the process and place that is provided to the community in the construction of decision-making . Different people bring different assessments to a situation and these must be taken into account . In this study, community intervention was focused in the surveillance phase to guarantee early triatomines detection. Furthermore, it promoted an active and positive attitude in local population and the householders were able to clarify their doubts related to the transmission and prevention of Chagas Disease.
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. There are many works showing a cost decrease when community collaborates in surveillance [11, 17, 30, 34, 35, 36, 37] 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 . Also, in Santiago del Estero (Argentina) a very complete analysis was carried out, considering community intervention and the cost-effectiveness was estimated in attack phase where householders sprayed owns houses . 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.
In La Rioja province, it is assumed that a house should be sprayed when PPCHLR technicians corroborate T. infestans presence. PPCHLR searching is carried out during the day, however, the householders can be carried out it during the day and at night. In this case, the probability of finding dispersants is higher due to the T. infestans peak activity occur between 7 and 10 pm . Our results showed that most of the insects collected by householders were found in ID (52/79), which 13.5% (7/52) were found on the external wall, light or in the mosquito netting, so it is assumed as dispersants from other sources. For this reason, it is important to establish an appropriate response to each T. infestans collected by a householder. Especially, if T. infestans is a female, represents a particular epidemiological risk as colonizers of houses, justifying a control intervention. It is known that each fertilized female can lay between 100 and 600 eggs in her lifetime . Dispersant females carried numerous eggs within the oviducts to ensure successful colonization of a new habitat , so it is necessary not to postpone control actions. In the case of triatomines dispersant collection, the possibilities of invasion can be reduced by physical protection (such as mosquito netting) .
In order to control circuit function correctly, we proposed that householders inform about the T. infestans presence in their houses and notify to Municipality. For this, is necessary that each Department count on a municipal referent verifies this species presence. If houses are T. infestans positive, personnel designated for this purpose spray them and their 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 increase the treatment frequency PPCHLR over higher infestation areas. To understand the variables associated with infestation in the area help in design of entomological surveillance implementation .
Heterogeneity in infestation probability is known in areas of Gran Chaco [4, 5, 13, 34, 39]. In addition, T. infestans domestic infestation estimated with community participation allowed to detect a spatially heterogeneous infestation in CBD.
Within this department, southern zone presented the highest risk of infestation. Heterogeneity in the infestation risk could be associated to climatic conditions due to southern zone presented higher temperature and lower humidity in relation to the other ones. These climatic conditions could allow an optimal growth of the species as was observed by other authors [34, 40, 41]. Although the climatic variables ranges in the different zones would be within their optimal values, the zone with the highest temperature and lowest humidity would provide a better development of T. infestans populations. It is known that optimal levels for most of triatomines are temperatures of 26–29 °C and 70% or less of relative humidity. When temperatures are higher at this range, insects need higher humidity to prevent dehydration. If the climate conditions are not enough wet, the dehydration danger can only be solved by increasing the blood meals number, producing a life cycle reduction with a population increase . Another factor that could explain zonal differences was the PD presence due to those gave refuge and feeding sources for triatomines . In southern zone (Agua Blanca and Pinchas), PD with T. infestans presence in DU evaluated (6/22) was observed, not so in the north and central zones (Table 2). All these results showed that there are several factors that promote T. infestans presence, particularly in this zone.
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.
This work allowed to verify that involving community in entomological surveillance reduced costs, covered a greater surface and a proportion of DU evaluated, encouraged early infestation detection and is the first step in stimulating control interventions. 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.