Abstract:
BACKGROUND : Malaria control in Africa relies heavily on indoor vector management, primarily indoor residual
spraying and insecticide treated bed nets. Little is known about outdoor biting behaviour or even the dynamics of
indoor biting and infection risk of sleeping household occupants. In this paper we explore the preferred biting sites
on the human body and some of the ramifications regarding infection risk and exposure management.
METHODS : We undertook whole-night human landing catches of Anopheles arabiensis in South Africa and Anopheles
gambiae s.s. and Anopheles funestus in Uganda, for seated persons wearing short sleeve shirts, short pants, and bare
legs, ankles and feet. Catches were kept separate for different body regions and capture sessions. All An. gambiae s.
l. and An. funestus group individuals were identified to species level by PCR.
RESULTS : Three of the main vectors of malaria in Africa (An. arabiensis, An. gambiae s.s. and An. funestus) all have a
preference for feeding close to ground level, which is manifested as a strong propensity (77.3% – 100%) for biting
on lower leg, ankles and feet of people seated either indoors or outdoors, but somewhat randomly along the lower
edge of the body in contact with the surface when lying down. If the lower extremities of the legs (below mid-calf
level) of seated people are protected and therefore exclude access to this body region, vector mosquitoes do not
move higher up the body to feed at alternate body sites, instead resulting in a high (58.5% - 68.8%) reduction in
biting intensity by these three species.
CONCLUSIONS : Protecting the lower limbs of people outdoors at night can achieve a major reduction in biting
intensity by malaria vector mosquitoes. Persons sleeping at floor level bear a disproportionate risk of being bitten at
night because this is the preferred height for feeding by the primary vector species. Therefore it is critical to protect
children sleeping at floor level (bednets; repellent-impregnated blankets or sheets, etc.). Additionally, the
opportunity exists for the development of inexpensive repellent-impregnated anklets and/or sandals to discourage
vectors feeding on the lower legs under outdoor conditions at night.
