Skip to Navigation
London School of Hygiene & Tropical Medicine Malaria Centre

Malaria clinical trials and studies

Species shifts in the Anopheles gambiae complex: do LLINs successfully control Anopheles arabiensis?

LSHTM investigators:
Richard Oxborough, Jane Bruce & Mark Rowland.
External collaborators:
Franklin Mosha & Jovin Kitua (Kilimanjaro Christian Medical University College, Tanzania); Stephen Magesa, Robert Malima & Patrick Tungu (National Institute for Medical Research, Tanzania).
Funding body:
The Bill & Melinda Gates Foundation through the Gates Malaria Partnership.

Coverage of conventional and long-lasting insecticide treated nets (ITNs and LLINs) in parts of E Africa are associated with reductions in local malaria burdens.

Between 2005-2006 six experimental hut trials of ITNs and LLINs were conducted in parallel at two field stations in northeastern Tanzania; the first was in Lower Moshi Rice Irrigation Zone, an area where An. arabiensis predominates, and the second was in coastal Muheza where An. gambiae and An. funestus predominate. Five pyrethroid and one carbamate insecticide were evaluated on nets in terms of insecticide-induced mortality, blood-feeding inhibition and exiting rates.

Mortality of An. arabiensis was consistently lower than that of An. gambiae and An. funestus. Mortality rates in trials with pyrethroid treated nets ranged from 25-52% for An. arabiensis, 63-88% for An. gambiae s.s. and 53-78% for An. funestus

LLINs and ITNs treated with pyrethroids were more effective at killing An. gambiae and An. funestus than An. arabiensis. This could be a major contributing factor to the species shifts observed in East Africa following the scale up of LLINs.

With continued expansion of LLIN coverage in Africa An. arabiensis is likely to remain responsible for residual malaria transmission, and species shifts might be reported over larger areas.