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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, Azizi, Salum, Drakeley, Christopher J, Kachur, S Patrick and Killeen, Gerry ORCID: (2011) 'Increased proportions of outdoor feeding among residual malaria vector populations following increased use of insecticide-treated nets in rural Tanzania'. Malaria Journal, Vol 10, Issue 1, p. 80.

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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.

Item Type: Article
Additional Information: The electronic version of this article is the complete one and can be found online at:
Subjects: QX Parasitology > Insects. Other Parasites > QX 515 Anopheles
QX Parasitology > Insects. Other Parasites > QX 600 Insect control. Tick control
WC Communicable Diseases > Tropical and Parasitic Diseases > WC 765 Prevention and control
Digital Object Identifer (DOI):
Depositing User: Users 183 not found.
Date Deposited: 21 Jun 2011 08:21
Last Modified: 25 Jan 2022 09:40


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