S.W. Lindsay, R. McGready and G.E.L. Walraven
Malaria during pregnancy is a major threat to the health of mothers and their children, during development in utero and early infancy (Brabin, 1991; Menendez, 1995). The severity of this infection depends to a large extent on the degree of exposure to malaria parasites and, consequently, the development of protective immunity in these women (Table 6.1). Since there is a general lowering of immunity during pregnancy, pregnant women are more likely to be infected, have higher parasite densities and experience more clinical episodes of malaria than when not pregnant (Diagne et al., 1997) in high transmission areas. In many cases these infections lead to anaemia and can be an important indirect cause of maternal mortality (Granja et al., 1998). Malaria infections also harm the foetus. Parasites can cause abortions and stillbirths, particularly in areas of low transmission, where immunity is low. More commonly, infection with malaria leads to low birthweight babies, mainly as a result of intra-uterine growth retardation and less often as preterm birth (Reinhart, 1978; Watkinson et al., 1985; Dolan et al., 1993; Meuris et al., 1993; Garner et al., 1994; Nosten et al., 1994; Steketee et al., 1996a), as well as an increase in early infant mortality (Brabin, 1991; Meuris et al., 1993; Menendez, 1995; Sullivan et al., 1999).
Although the precise nature of the pathophysiology of malaria infections and the resulting immune responses are poorly understood, some general patterns are clear. In areas of low or epidemic transmission, all pregnant women are vulnerable to infection. Where malaria transmission is intense, the harmful effects of malaria during pregnancy are confined largely to women in their first and second pregnancy, before the development of a strong protective immunity (McGregor et al., 1983). One of the reasons for this protection is that a sub-population of parasites that sequester in the placenta initiate the production of antibodies during the first pregnancy that are protective against parasites in subsequent pregnancies (Fried & Duffy, 1996). Consequently, rates of maternal malaria decline accordingly in multiparous women. Treating infected women from malaria endemic areas is difficult since many of these women remain asymptomatic, so do not seek care for malaria (Steketee et al., 1996b), and placental malaria is often not accompanied by a patent peripheral parasitaemia, so infection cannot be reliably screened for