Increased proportions of outdoor feeding among residual malaria vector populations following increased use of insecticide-treated nets in rural Tanzania

Russell, Tanya L., Govella, Nicodem J., Azizi, Salum, Drakeley, Christopher J., Kachur, S. Patrick and Killeen, Gerry F. (2011) Increased proportions of outdoor feeding among residual malaria vector populations following increased use of insecticide-treated nets in rural Tanzania. Malaria Journal, 10 80.1-80.10. doi:10.1186/1475-2875-10-80


Author Russell, Tanya L.
Govella, Nicodem J.
Azizi, Salum
Drakeley, Christopher J.
Kachur, S. Patrick
Killeen, Gerry F.
Title Increased proportions of outdoor feeding among residual malaria vector populations following increased use of insecticide-treated nets in rural Tanzania
Journal name Malaria Journal   Check publisher's open access policy
ISSN 1475-2875
Publication date 2011-04
Sub-type Article (original research)
DOI 10.1186/1475-2875-10-80
Open Access Status DOI
Volume 10
Start page 80.1
End page 80.10
Total pages 10
Place of publication London, England, U.K.
Publisher BioMed Central
Collection year 2012
Language eng
Formatted abstract
Background
Insecticide-treated nets (ITNs) and indoor residual spraying (IRS) represent the front-line tools for malaria vector control globally, but are optimally effective where the majority of baseline transmission occurs indoors. In the surveyed area of rural southern Tanzania, bed net use steadily increased over the last decade, reducing malaria transmission intensity by 94%.
Methods
Starting before bed nets were introduced (1997), and then after two milestones of net use had been reached-75% community-wide use of untreated nets (2004) and then 47% use of ITNs (2009)-hourly biting rates of malaria vectors from the Anopheles gambiae complex and Anopheles funestus group were surveyed.
Results
In 1997, An. gambiae s.l. and An. funestus mosquitoes exhibited a tendency to bite humans inside houses late at night. For An. gambiae s.l., by 2009, nocturnal activity was less (p = 0.0018). At this time, the sibling species composition of the complex had shifted from predominantly An. gambiae s.s. to predominantly An. arabiensis. For An. funestus, by 2009, nocturnal activity was less (p = 0.0054) as well as the proportion biting indoors (p < 0.0001). At this time, An. funestus s.s. remained the predominant species within this group. As a consequence of these altered feeding patterns, the proportion (mean ± standard error) of human contact with mosquitoes (bites per person per night) occurring indoors dropped from 0.99 ± 0.002 in 1997 to 0.82 ± 0.008 in 2009 for the An. gambiae complex (p = 0.0143) and from 1.00 ± <0.001 to only 0.50 ± 0.048 for the An. funestus complex (p = 0.0004) over the same time period.
Conclusions
High usage of ITNs can dramatically alter African vector populations so that intense, predominantly indoor transmission is replaced by greatly lowered residual transmission, a greater proportion of which occurs outdoors. Regardless of the underlying mechanism, the residual, self-sustaining transmission will respond poorly to further insecticidal measures within houses. Additional vector control tools which target outdoor biting mosquitoes at the adult or immature stages are required to complement ITNs and IRS.
Keyword Anopheles-gambiae complex
Bed Nets
Child-mortality
Morbidity
Mosquitos
Polymerase-chain-reaction
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Australian Centre for International & Tropical Health
Official 2012 Collection
School of Public Health Publications
 
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Created: Mon, 19 Mar 2012, 13:35:57 EST by Geraldine Fitzgerald on behalf of School of Public Health