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

@entity1 @entity311 @entity314 @entity313
BACKGROUND: Insecticide-treated nets (ITNs) and indoor residual spraying (IRS) represent the front-line tools for @entity311 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 @entity311 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 @entity311 vectors from the @entity313 complex and @entity314 group were surveyed. RESULTS: In 1997, An. gambiae s.l. and An. funestus mosquitoes exhibited a tendency to bite @entity1 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 @entity1 contact with mosquitoes (bites per @entity1 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.
