Leishmaniasis sand fly vector density reduction is less marked in destitute housing after insecticide thermal fogging

Abstract

BackgroundInsecticide thermal fogging (ITF) is a tool to control vector borne diseases. Insecticide application success for vector control has been associated with housing materials and architecture. Vector abundance is correlated with weather changes. Nevertheless, housing quality and weather impacts on vector abundance have been unaccounted for in most New World insecticide control trials for leishmaniasis vectors.MethodsWe conducted a 15 month insecticide control trial that included two deltamethrin [6 mg a.i.m-2] based ITF interventions in 12 of 24 monitored houses at Trinidad de Las Minas, a hyperendemic cutaneous leishmaniasis transmission village in western Panamá. During the study we followed sand fly (SF) abundance, keeping track of rainfall and quantified housing quality using an index based on architecture and construction materials.ResultsWe found a 50 to 80% reduction in SF density in the fogged houses when compared with control houses, while controlling for seasonal changes in SF abundance associated with rainfall. We found heterogeneities in the reductions, as abundance changed according to SF species: Lutzomyia gomezi, Lu. panamensis, Lu. dysponeta and Lu. triramula reduced in density between 40% and 90% after ITF. In contrast, Lu. trapidoi density increased 5% after ITF. Differences in the impact of ITF were associated with housing quality, the most destitute houses, i.e., those with features that ease insect entrance, had a disproportionally larger SF abundance, in some cases with increased domiciliary SF density following the ITF.ConclusionOur results suggest the potential of insecticide application to control SF density and leishmaniasis transmission could depend on housing quality beyond insecticide efficiency.

Exposure to Phlebotomus argentipes (Diptera, Psychodidae, Phlebotominae) Sand Flies in Rural Areas of Bihar, India: The Role of Housing Conditions

“…Independent of housing conditions, socio-economic status was also associated with vector density; the poorer the household, the higher its exposure to sand flies. Similar associations were observed for other phlebotomine sand fly species in Panama [16]. In an earlier study in the same area in Bihar we were able to show statistically significant associations between housing conditions and socio economic status on one side and VL on the other [21].…”

Characterization of a recent malaria outbreak in the autonomous indigenous region of Guna Yala, Panama

“…infestation [24, 25]. Other risk factors such as destitute housing, which is inappropriate for residual insecticide application [26], and the rejection by the Gunas of different vector control measures, also contribute to the vulnerability of this region [22]. In fact, recent studies have shown that traditional house architecture found in Gunas communities is a risk factor for malaria transmission [23, 27].…”

Housing Characteristics and Leishmaniasis: A Systematic Review

“…10,11 One of the most widespread methods for sand fly control is indoor residual insecticide spraying [12][13][14] ; however, such measure becomes unsustainable over time, 15 and even after spraying, the characteristics, including floor, walls, and roof materials, and quality of the house could hamper sand fly control. 16,17 Some specific housing characteristics have been associated with various health problems, 7,18,19 including vectorborne diseases. 20,21 "Unhealthy" houses are more frequent in rural areas, were leishmaniasis is more frequent.…”