Spatio-temporal heterogeneity of malaria vectors in northern Zambia: implications for vector control

Abstract

BackgroundDespite large reductions in malaria burden across Zambia, some regions continue to experience extremely high malaria transmission. In Nchelenge District, Luapula Province, northern Zambia, almost half the human population carries parasites. Intervention coverage has increased substantially over the past decade, but comprehensive district-wide entomological studies to guide delivery of vector control measures are lacking. This study describes the bionomics and spatio-temporal patterns of malaria vectors in Nchelenge over a two and a half year period, investigates what household factors are associated with high vector densities and determines why vector control may not have been effective in the past to better guide future control efforts.MethodsBetween April 2012 and September 2014, twenty-seven households from across Nchelenge District were randomly selected for monthly light trap collections of mosquitoes. Anopheline mosquitoes were identified morphologically and molecularly to species. Foraging rates were estimated and sporozoite rates were determined by circumsporozoite ELISAs to calculate annual entomological inoculation rates. Blood feeding rates and host preference were determined by PCR. Zero-inflated negative binomial models measured environmental and household factors associated with mosquito abundance at study households such as season, proximity to the lake, and use of vector control measures.ResultsThe dominant species in Nchelenge was An. funestus (s.s.) with An. gambiae (s.s.) as a secondary vector. Both vectors were found together in large numbers across the district and the combined EIRs of the two vectors exceeded 80 infectious bites per person per annum. An. funestus household densities increased in the dry season whilst An. gambiae surged during the rains. Presence of insecticide treated nets (ITNs) and closed eaves in the houses were found to be associated with fewer numbers of An. gambiae but not An. funestus. There was no association with indoor residual spraying (IRS).ConclusionIn Nchelenge, the co-existence of two highly anthropophagic vectors, present throughout the year, is likely to be driving the high malaria transmission evident in the district. The vectors here have been shown to be highly resistant to pyrethroids used for IRS during the study. Vector control interventions in this area would have to be multifaceted and district-wide for effective control of malaria.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1786-9) contains supplementary material, which is available to authorized users.

Benchmarking insecticide resistance intensity bioassays for Anopheles malaria vector species against resistance phenotypes of known epidemiological significance

“…funestus from Nchelenge using time exposures [28] and ZAMF in this study (both of which were based on the use of F1 progeny from wild-caught females and can, therefore, be suitably representative of the wild population), is likely to lead to operational failure of a pyrethroid-based IRS programme in this region. This prediction is borne out by studies published recently describing the malaria epidemiology and vector bionomics in Nchelenge [29, 30]. Zambia has revised its pyrethroid-based IRS policy to include the use of organophosphate insecticides because of burgeoning pyrethroid resistance in target vector populations, especially An.…”

Papyrus, Forest Resources and Rural Livelihoods: A Village Computable General Equilibrium Analysis from Northern Zambia

“…Average monthly temperature does not vary greatly throughout the year, with an average of about 24˚C, but daily fluctuations can be large with lows of 11˚C in the winter and highs of 34˚C in the hot season. Rainfall follows a seasonal pattern, with a peak of 2700 mm in the rainy months and close to 0 mm during the dry months [61] [62]. Mantapala lies about 20 km east of Nchelenge town, accessible by a gravel road.…”

Geographically extensive larval surveys reveal an unexpected scarcity of primary vector mosquitoes in a region of persistent malaria transmission in western Zambia

“…funestus s.s. and An. gambiae s.s., although detailed entomological studies have been undertaken only comparatively recently [45,46]. Despite the continued high prevalence of malaria in Barotseland, however, An.…”

“…[47], whilst in southern Zambia An. arabiensis is thought to be the primary vector [46]. However, although An.…”