Acute and chronic consequences of childhood malaria include uncomplicated febrile episodes with parasitemia, and anemia. Data from a large meta-analysis suggest that ITN use under stable transmission conditions roughly halves mild malaria episodes in children under five (Lengeler, 2001). In a nonrandomized trial of ITNs in southwestern Tanzania, treated nets conferred protective efficacy of 62 and 63 percent, respectively, on parasitemia and anemia in children under 5 (Abdulla et al., 2001). In an area of high perennial transmission in western Kenya, ITNs delayed the time to first infection in infants from 4.5 to 10.7 months (ter Kuile et al., 2003a).
Repeated malaria infection also causes anemia and morbidity in pregnant women and newborns. Four randomized controlled trials of ITNs in pregnancy have shown variable benefits in different transmission settings. In Thailand and The Gambia (areas with lower, seasonal transmission), ITNs significantly reduced malaria parasitemia and maternal anemia (Dolan et al., 1993; D’Alessandro et al., 1996); in The Gambia, they also increased birth weight (D’Alessandro et al., 1996). However, similar benefits were not seen in areas with more intense transmission (coastal Kenya and Ghana) (Shulman et al., 1998; Browne et al., 2001), raising concern that ITNs might not protect pregnant women in areas with a very high EIR. This concern was allayed by the most recent findings.
In the western Kenya trial, complete data were available in nearly 3,000 pregnancies (ter Kuile et al., 2003b). Before the study began, up to one-third of all infants were born preterm, small for gestational age, or with low birth weight. ITN-using pregnant women (gravidae 1-4) experienced a 38 percent reduction in maternal parasitemia, a 47 percent reduction in malarial anemia, and a 35 percent reduction in placental malaria at the time of delivery, while their newborns demonstrated a 28 percent reduction in low birth weight.
In addition to conferring benefits upon individual users, ITNs can protect nonusers within ITN households as well as nonusers in nearby houses. Such effects were first noted in early village-scale ITN trials in Burkina Faso (Robert and Carnevale, 1991), Tanzania (Magesa et al., 1991), Kenya (Beach et al., 1993), and Zaire (Karch et al., 1993). More recent ITN studies have confirmed community-wide reductions in vector populations (Hii et al., 1997; Binka et al., 1998; Hii et al., 2000; Howard et al., 2000; Maxwell et al., 2002). Some ITN trial data have even demonstrated spatial effects on health. In Ghana, child mortality increased by 6.7 percent for every 100 m away from an intervention compound (Binka et al., 1998),