Vector control has substantially reduced the incidence of Chagas disease in Latin America. However, the presence of residual foci and triatomines reinfestation in houses persists, suggesting that entomological surveillance should play a crucial role in the long term (6).
At the beginning of the year 2.000, the endemic area of Bolivia had a 55% infestation rate of houses by T. infestans. Given this situation, the PNCH with a loan from the Inter-American Development Bank (IDB) and technical support from PAHO / WHO, developed actions of Vector control in a sustained manner accompanied by entomological evaluations with the methodology Hour/Man/House. By 2008, at the conclusion of these continuous and contiguous vector control activities, the impact of the actions reduced the infestation of T. infestans in houses to less than 3% in the entire endemic area (4).
The low sensitivity of the Time/Man/House (T/M/H) method in the entomological search in a situation of low infestation and low density of vector colonies, began to be a technical problem of relevance (6). The need to detect residual foci or events of re-infestation of houses by triatomines, was undoubtedly one of the main challenges in the transition from a vector control and monitoring model from vertical to a horizontal structure and participatory model.
The sensitivity of vector detection methods is generally unsatisfactory, however, the denunciation of the presence of vectors by the inhabitants, which we call "community participation" method (PC) is clearly superior to the other methods, including active search method (BA) by trained institutional staff and the so-called “sensing devices” (5, 6).
There are many existing evidences that corroborate this statement. Among them, we can highlight the works of Garcia-Zapata et al, (13) in Brazil, in which the detection of vectors was between 10 and 16 times more likely using “participatory” strategies than those when the program agents visited the houses; de Gurtler et al, (14) in Argentina, where after four years of follow-up (1993–1996) in 98 houses, the chances of detecting T. infestans within the houses were seven times higher with PC than with BA; from Feliciangeli et al, (15) in Venezuela, which showed a PC effectiveness much higher than that of BA (with or without repellent/irritant substances): the chances of detection were more than 20 times higher with the first method.
In a period of two years (2.007–2.009), the PNCH in Bolivia evaluating the sensitivity of the method with community participation (CP) compared to the T/M/H, obtained similar results to those described in other countries, which led to design the entomological surveillance card with community participation, an instrument proposed for the present study (Fig. 2).
Between 2.011 and 2.018, 36,221 entomological surveillance cards were distributed in patients who requested care in five CPs in both the urban and rural areas of the departments of Cochabamba, Tarija and Chuquisaca. The data obtained from participation 27,643 (76%) demonstrate a high commitment of patients and their families to actively participate in the search for the vector in the house. One of the relevant factors for this high participation is due to the motivation that the health personnel of the CPs (doctors and nurses) stimulated in the patients as part of the model of integral healthcare for the patient with Chagas disease (10). Similar response was evidenced by Urquiola (16) when a “motivational training” was implemented in a rural community, prior to an entomological evaluation intervention with PC, with active support from its community leaders, compared to another community that did not receive motivational training. The results show a participation in monitoring with PC of 60% compared to 1% in the community that did not receive the motivational training respectively.
According to Abad et al (6), it is suggested that stakeholder participation at all stages of the process, from planning to final evaluation, would probably improve PC-based strategies. Several authors suggest as well that a component of education and communication adapted to the socio-cultural environment of the community is obviously necessary to stimulate participation and notification (17, 18, 19)
The average vector infestation in the five CPs reached 3.1% (852 positive dwellings of a sample of 27,643 dwellings), according to PNCH data in 2018 (unpublished PNCH information), in Bolivia the vector infestation reaches an average of 1.4%.
The data found in the study confirm that the global vector infestation has remained below 3% for more than a decade in the entire endemic area of the mesothermal valleys of Bolivia, where the presence of the T. infestans species predominates. However, it should be noted that in practice, failures in the detection of vectors are inevitable, particularly when the density of the insect population is low (20), which would lead to an underestimation of the entomological indicators and consequences in the decision making of the operators of the Chagas problem (21).
According to the data obtained in urban and rural areas, the CPs Cercado and Punata in the department of Cochabamba are the ones that report a greater number of positive homes (3.8% and 10% respectively), when compared to the other CPs of Chuquisaca and Tarija (Table 1).
In the same way, the data in the three departments show a concentration of positive houses to the presence of the vector in the rural and peri-urban areas when compared to the urban area of the capital cities. This situation is more noticeable and accentuated in the peri-urban belt of the city of Cochabamba, possibly due to several factors among which we can highlight: the ideal environmental conditions for the proliferation of the T. infestans species (22, 23), human settlements in a situation of poverty established to the east, south and west of the peri-urban belt of the city, partly due to a country-city migration phenomenon since the 1980s (24), and the historical presence of wild foci of T. infestans near the peri-urban areas where families permanently report the presence of the vector (22, 25, 26) (Table 2).
The data show that the capture of triatomines in the intra-domicile is greater when compared to the capture in the peri-domicile (66% and 41% respectively). The PC method, in addition to being more sensitive in detecting triatomine colonies at low densities, also demonstrates a greater capture sensitivity in the intra-domicile than in the peri-domicile, probably because capture spans anywhere from three to five days and also because triatomines.
have nocturnal habits and can be more noticeable by family members when they leave their hiding places for feeding in people's bedrooms (Table 2).
The presence of triatomines infected with Trypanosomatideos in the houses that checked positive, is 6% in the study area, still finding active domestic cycles in rural and peri-urban areas and not in urban areas where triatomines with parasites were not reported during the seven years of monitoring. According to historical information of the rural area of Cotapachi, Quillacollo in the department of Cochabamba, the Tripano/Triatominic (T/T) Index of T. infestans captured at house as in triatomines captured in wild areas was 67.4% and 60% respectively (23). This information reinforces the need to permanently maintain entomological surveillance in houses near natural areas of wild foci of T. infestans, in order to prevent reinfestation of triatomine dwellings infected with T. cruzi.
Note that the method used to detect the parasite in the vector insect (observation under an optical microscope), is not very sensitive compared to triatomine nucleic acid’s detection by amplification based on the Polymerase Chain Reaction methods (PCR). However, PCR methods are not widely available, and its application is limited. In the context of our study, the method used to detect triatomines by the departmental and municipal entomological laboratories in the study area was the direct observation of the parasites through optical microscope.
The observations during the seasons of the year, show that in the spring season (September to December) was the period where there was a higher average of T. infestans positive houses detected by the families participating in the study in the three departments of Bolivia. Similar information was also observed at wild-spot capture sites of Andean T. infestans in the Cotapachi Cochabamba area, where the densities of T. infestans were highest during the hot season (September to January) (26). These findings could probably be related to the biology of the insect vector itself.