Risk factors for malaria infection prevalence and household vector density between mass distribution campaigns of long-l
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Malaria Journal Open Access
RESEARCH
Risk factors for malaria infection prevalence and household vector density between mass distribution campaigns of long‑lasting insecticidal nets in North‑western Tanzania Jacklin F. Mosha1* , Eliud Lukole1, J. Derek Charlwood2, Alexandra Wright2, Mark Rowland2, Olivia Bullock2, Alphaxard Manjurano1, William Kisinza4, Franklin W. Mosha3, Immo Kleinschmidt5 and Natacha Protopopoff2
Abstract Background: Long-lasting insecticidal nets (LLINs) are the most widely deployed vector control intervention in subSaharan Africa to prevent malaria. Recent reports indicate selection of pyrethroid insecticide resistance is widespread in mosquito vectors. This paper explores risk factors associated with malaria infection prevalence and vector density between mass distribution campaigns, changes in net coverage, and loss of protection in an area of high pyrethroid resistance in Northwest Tanzania. Methods: A cross sectional malaria survey of 3456 children was undertaken in 2014 in Muleba district, Kagera region west of Lake Victoria. Vector density was assessed using indoor light traps and outdoor tent traps. Anophelines were identified to species using PCR and tested for Plasmodium falciparum circumsporozoite protein. Logistic regression was used to identify household and environmental factors associated with malaria infection and regression binomial negative for vector density. Results: LLIN use was 27.7%. Only 16.9% of households had sufficient nets to cover all sleeping places. Malaria infection was independently associated with access to LLINs (OR: 0.57; 95% CI 0.34–0.98). LLINs less than 2 years old were slightly more protective than older LLINs (53 vs 65% prevalence of infection); however, there was no evidence that LLINs in good condition (hole index 10–25 cm (size 3) and > 25 cm (size 4), and proportional hole index (pHI) as an estimate of hole area was calculated. For purposes of analysis the LLINs were further categorized into three groups: good condition (pHI 0–64), moderately damaged (pHI 65–642) and badly damaged (pHI > 643) [21]. Entomological monitoring
From November 2014 to January 2015, indoor mosquito collections were conducted using CDC light traps in 14–21 randomly selected houses per cluster for one night only. The light traps were installed at the foot of a bed occupied by a family member sleeping under a LLIN. In addition, two or three furvela tent trap collections per cluster [22] were conducted for one night to assess outdoor density. They were placed near to houses selected for indoor light trap collections. Further information on house structure, livestock, and LLINs access and usage was collected. All mosquitoes collected were morphologically identified to species [23]. Up to 20 Anopheline
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mosquitoes per house were subsequently tested for Plasmodium falciparum circumsporozoite protein (Pf-CSP) using ELISA [24]. A sub-sample of An. gambiae s.l. was tested using real time PCR Taq Man assay to distinguish between the two sibling species An. gambia
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