Intensified Surveillance and Insecticide-based Control of the Chagas Disease Vector Triatoma infestans in the Argentinean Chaco

Abstract

BackgroundThe elimination of Triatoma infestans, the main Chagas disease vector in the Gran Chaco region, remains elusive. We implemented an intensified control strategy based on full-coverage pyrethroid spraying, followed by frequent vector surveillance and immediate selective insecticide treatment of detected foci in a well-defined rural area in northeastern Argentina with moderate pyrethroid resistance. We assessed long-term impacts, and identified factors and procedures affecting spray effectiveness.Methods and FindingsAfter initial control interventions, timed-manual searches were performed by skilled personnel in 4,053 sites of 353–411 houses inspected every 4–7 months over a 35-month period. Residual insecticide spraying was less effective than expected throughout the three-year period, mainly because of the occurrence of moderate pyrethroid resistance and the limited effectiveness of selective treatment of infested sites only. After initial interventions, peridomestic infestation prevalence always exceeded domestic infestation, and timed-manual searches consistently outperformed householders' bug detection, except in domiciles. Most of the infestations occurred in houses infested at baseline, and were restricted to four main ecotopes. Houses with an early persistent infestation were spatially aggregated up to a distance of 2.5 km. An Akaike-based multi-model inference approach showed that new site-level infestations increased substantially with the local availability of appropriate refugia for triatomine bugs, and with proximity to the nearest site found infested at one or two preceding surveys.Conclusions and SignificanceCurrent vector control procedures have limited effectiveness in the Gran Chaco. Selective insecticide sprays must include all sites within the infested house compound. The suppression of T. infestans in rural areas with moderate pyrethroid resistance requires increased efforts and appropriate management actions. In addition to careful, systematic insecticide applications, housing improvement and development policies that improve material conditions of rural villagers and reduce habitat suitability for bugs will contribute substantially to sustainable vector and disease control in the Gran Chaco.

Modeling Disease Vector Occurrence When Detection Is Imperfect II: Drivers of Site-Occupancy by Synanthropic Triatoma brasiliensis in the Brazilian Northeast

“…We note that while multi-model inference has been used in a few studies similar to ours [32]–[34], the formal treatment of detection failures has hardly entered the vector ecology literature thus far [14], [28], [29], [35], [36]. Yet, as discussed below, standard approaches can yield biased effect-size estimates and SEs; site-occupancy models may provide a more reliable and realistic picture of key population parameters and their environmental correlates [15], [16].…”

Heterogeneities in the Ecoepidemiology of Trypanosoma cruzi Infection in Rural Communities of the Argentinean Chaco

“…This pattern may be explained by one or more of the following mechanisms: (1) misclassification of house infestation status caused by the limited sensitivity of the methods used to detect bugs and bug infection, 14,30,31 perhaps combined with more efficient parasite transmission at low infected bug densities; (2) vertical transmission 15,16 ; (3) undocumented changes in exposure to bugs in the recent past; and (4) other sources of infection not accounted for, including orally acquired infections, travel history to other infested houses or villages, and transmission mediated by sylvatic triatomine bugs (apparently of minor local significance). 32 In support of undocumented changes in exposure to bugs (mechanism 3), differences between study villages in agerelated trends in dog infection and the lack of fit of the catalytic model 13,19 provide strong evidence that the risk of infection had not been spatially and temporally homogeneous over the previous 5-10 years.…”

A motorized vehicle-mounted sprayer as a new tool for Chagas disease vector control

“…The trial also provided updated information on the occurrence of house infestation with T. infestans and other triatomine species in northern Mendoza province, documenting high bug abundance in domestic and peridomestic sites. Peridomestic (re)infestation by T. infestans has been documented elsewhere in the Gran Chaco ecoregion 19,20,21,22,23,24 but not in Mendoza province.…”

“…House reinfestation after residual insecticide spraying may be explained by different processes: (i) incomplete spray coverage of target sites causing control failures; (ii) low susceptibility to the insecticide; and (iii) extradomiciliary, residual or wild foci of T. infestans 22,27,28,29 . Regarding (i), the presence of residual foci of T. infestans can be inferred from the coincidence of sites persistently infested before and after insecticide sprays, mainly occurring in large, structurally complex peridomestic structures such as goat corrals 27,30 .…”