Improved vector control of Triatoma infestans limited by emerging pyrethroid resistance across an urban-to-rural gradient in the Argentine Chaco

Background The sustainable elimination of Triatoma infestans in the Gran Chaco region represents an enduring challenge. Following the limited effects of a routine pyrethroid insecticide spraying campaign conducted over 2011–2013 (first period) in Avia Terai, an endemic municipality with approximately 2300 houses, we implemented a rapid-impact intervention package to suppress house infestation across the urban-to-rural gradient over 2015–2019 (second period). Here, we assess their impacts and whether persisting infestations were associated with pyrethroid resistance. Methods The 2011–2013 campaign achieved a limited detection and spray coverage across settings (< 68%), more so during the surveillance phase. Following community mobilization and school-based interventions, the 2015–2019 program assessed baseline house infestation using a stratified sampling strategy; sprayed all rural houses with suspension concentrate beta-cypermethrin, and selectively sprayed infested and adjacent houses in urban and peri-urban settings; and monitored house infestation and performed selective treatments over the follow-up. Results Over the first period, house infestation returned to pre-intervention levels within 3–4 years. The adjusted relative odds of house infestation between 2011–2013 and 2015–2016 differed very little (adj. OR: 1.17, 95% CI 0.91–1.51). Over the second period, infestation decreased significantly between 0 and 1 year post-spraying (YPS) (adj. OR: 0.36, 95% CI 0.28–0.46), with heterogeneous effects across the gradient. Mean bug abundance also dropped between 0 and 1 YPS and thereafter remained stable in rural and peri-urban areas. Using multiple regression models, house infestation and bug abundance at 1 YPS were 3–4 times higher if the house had been infested before treatment, or was scored as high-risk or non-participating. No low-risk house was ever infested. Persistent foci over two successive surveys increased from 30.0 to 59.3% across the gradient. Infestation was more concentrated in peridomestic rather than domestic habitats. Discriminating-dose bioassays showed incipient or moderate pyrethroid resistance in 7% of 28 triatomine populations collected over 2015–2016 and in 83% of 52 post-spraying populations. Conclusions The intervention package was substantially more effective than the routine insecticide spraying campaign, though the effects were lower than predicted due to unexpected incipient or moderate pyrethroid resistance. Increased awareness and diagnosis of vector control failures in the Gran Chaco, including appropriate remedial actions, are greatly needed. Graphical abstract

A clinical-ecological study of a triple viral epidemic: Zika, Dengue and Chikungunya/ Um estudo clínico-ecológico de uma tripla epidemia viral: Zika, Dengue e Chikungunya

In Brazil, since 2015, co-circulation of three arboviruses, Dengue (DENV), Chikungunya (CHIKV) and Zika (ZIKV), have presented diagnostic challenges, due to their similar clinical manifestations. Our goal was to analyze cases of arboviral illness using key clinical features and to ascertain house infestation indices (HII) in the study area. A total of 28,064 medical records were analyzed by clinical-epidemiological criteria for DENV, ZIKV and CHIKV in 2015 and 2016 at the public health unit in Xerem, Duque de Caxias, Rio de Janeiro. The collection of vectors at home breeding sites in Xerem was performed to determine the HII, in March and June 2015. The total number of cases of suspected arboviral illness in 2015 was 969, of which 444 (45.8%) were due to DENV, 146 (15.1%) to ZIKV, and 11 (1.1%) to CHIKV. In 2016, the number of suspected cases of arboviral illness was 2019, of which 324 (16.0%) were classified as DENV, 779 (38.6%) as ZIKV, and 53 (2.60%) as CHIKV. The clinical manifestations prevalent in ZIKV were rash (67.8% to 79.5%) and pruritus (63.7% to 71.4%). The HII for the immature stages of Aedes in the study area, in March and June 2015, was 11.8% for Ae. aegypti and 8.1% for Ae. albopictus, both very high. There was a strong positive correlation observed for precipitation and HII for both vectors (Ae. aegypti and Ae. albopictus), but not for temperature levels. We conclude that a triple epidemic occurred in the studied area probably due to the high infestation rates and a naive population for the two newly introduced arboviruses; whilst there are no available specific laboratory tests a practical clinical diagnosis workout is crucial.

Attraction of Triatoma infestans (Klug) to adhesive yeast-baited trap under laboratory conditions

Existing methods to detect domestic triatomines have low sensitivity. As early house infestation detection is epidemiologically important, the exploration of better methods is required. Hence, we measured the attractiveness of a yeast-baited trap to adults and nymphs of Triatoma infestans, under laboratory conditions.The assays were conducted in an experimental arena, with an experimental and a control traps placed at opposite sides and one refuge in the center area. Insects where released and the number of triatomines in the yeast and control traps were counted, after 3, 6 and 24 hours of the beginning of the experiment. We use generalized linear models within a multimodel inference approach to model the number of insects in the trap, using insect age classes, time after assay initiation and date of the experiment as predictors.Our results show that the attraction to CO2 depends upon the life stage of the insects. During the 24 hours of experiment a constant number of adults were attracted to the yeast trap, while nymphs show attraction only up to the first three hours after the initiation of CO2 liberation. Undoubtedly, the orientation response to chemical cues deserves further studies to be fully understood.

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

Residual insecticide spraying still is the main tool used to suppress house infestations with Chagas disease vectors. While manual compression sprayers (MCS) have traditionally been used in Latin America, Mendoza's vector control program from Argentina introduced the use of a modified motorized vehicle-mounted sprayer (VMS) with apparent advantages over MCS. We conducted a randomized intervention trial to evaluate the effectiveness and selected components of the performance of MCS and VMS. We assessed house infestation by Triatoma infestans in 76 previously-infested houses at 0, 1, 4 and 12 months postintervention. Infestations were reduced substantially, with no significant differences between treatments. End-point infestations were restricted to peridomiciles. Although VMS required less time to complete the house spraying than MCS, both treatments had similar performance and did not suppress infestations completely. The main relative advantages of VMS were a reduced physical effort, especially under harsh field conditions, and potential gains in spray coverage per unit of time.