Beyond efficacy in water containers: Temephos and household entomological indices in six studies between 2005 and 2013 in Managua, Nicaragua

Abstract

BackgroundA cluster-randomized controlled trial of community mobilisation for dengue prevention in Mexico and Nicaragua reported, as a secondary finding, a higher risk of dengue virus infection in households where inspectors found temephos in water containers. Data from control sites in the preceding pilot study and the Nicaragua trial arm provided six time points (2005, 2006, 2007 and 2011, 2012, 2013) to examine potentially protective effects of temephos on entomological indices under every day conditions of the national vector control programme.MethodsThree household entomological indicators for Aedes aegypti breeding were Household Index, Households with pupae, and Pupae per Person. The primary exposure indicator at the six time points was temephos identified physically during the entomological inspection. A stricter criterion for exposure at four time points included households reporting temephos application during the last 30 days and temephos found on inspection. Using generalized linear mixed modelling with cluster as a random effect and temephos as a potential fixed effect, at each time point we examined possible determinants of lower entomological indicators.ResultsBetween 2005 and 2013, temephos exposure was not significantly associated with a reduction in any of the three entomological indices, whether or not the exposure indicator included timing of temephos application. In six of 18 multivariate models at the six time points, temephos exposure was associated with higher entomological indices; in these models, we could exclude any protective effect of temephos with 95% confidence.ConclusionOur failure to demonstrate a significant protective association between temephos and entomological indices might be explained by several factors. These include ecological adaptability of the vector, resistance of Aedes to the pesticide, operational deficiencies of vector control programme, or a decrease in preventive actions by households resulting from a false sense of protection fostered by the centralized government programme using chemical agents. Whatever the explanation, the implication is that temephos affords less protection under routine field conditions than expected from its efficacy under experimental conditions.Trial registration ISRCTN 27581154.Electronic supplementary materialThe online version of this article (doi:10.1186/s12889-017-4296-6) contains supplementary material, which is available to authorized users.

Seroprevalence, risk factor, and spatial analyses of Zika virus infection after the 2016 epidemic in Managua, Nicaragua

“…The documented preference of mosquitoes to feed on larger targets (36)(37)(38), the trend analysis, and the extended risk factor analysis all suggest that the large and continual increases in BSA during childhood and adolescence are primarily responsible for the sharp rise in ZIKV seroprevalence during that period. Aedes mosquitoes, the only known vectors for arboviruses in Nicaragua (46), are attracted to carbon dioxide and other components associated with human respiration and perspiration, which aid female Aedes mosquitoes in locating a blood meal (36,47). Larger and heavier persons expel more of these attractive components, explaining, together with exposed skin surface area, the general trend for older individuals to have a higher seroprevalence than younger individuals.…”

Effectiveness of Aedes-borne infectious disease control in Latin America and the Caribbean region: A scoping review

“…The lack of effect is possibly caused by negligence in eliminating breeding sites observed in the group that also applied temephos and the dilution of the insecticide in non-removable containers. A study in Nicaragua also did not demonstrate a positive effect of temephos combined with other interventions [ 110 ]. In the mentioned study, temephos exposure was not associated with a reduction in any entomological indices, and in some cases, temephos exposure was even associated with higher entomological outcomes [ 110 ].…”

DengueChat: A Social and Software Platform for Community-based Arbovirus Vector Control

“…In previous analyses, we found that three variables were significant predictors of vector density: use of abate during the past 30 days, regularity of water access, and participation in organizations. 34,44 We attempted to balance these variables between our intervention and control neighborhoods, as well as neighborhood size; therefore, we measured the level of each variable at 18 months in all neighborhoods. There was no significant difference in water access (P 5 0.7262) and participant organization (P 5 0.442).…”