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In the many areas where human malaria and helminthiases are co-endemic, schoolchildren often harbour the heaviest infections and suffer much of the associated morbidity, especially when co-infected. In one such area, the Buea district, in south–western Cameroon, two cross-sectional surveys, together covering 263 apparently healthy schoolchildren aged 4–12 years, were recently conducted. The prevalences of fever, malarial parasitaemia and intestinal helminth infections, the seroprevalences of anti-Plasmodium falciparum IgG and IgE and anti-glycosylphosphatidylinositol (anti-GPI) IgG, plasma concentrations of total IgE, and the incidence of anaemia were all investigated. The mean (S.D.) age of the study children was 7.56 (1.82) years. Overall, 156 (59.3%) of the children were found parasitaemic, with a geometric mean parasitaemia of 565 parasites/μml. Parasitaemia and fever were significantly associated (P=0.042). The children who lived at low altitude, attending schools that lay 400–650 m above sea level, had significantly higher parasitaemias than their high-altitude counterparts (P<0.01). At low altitude, the children attending government schools had significantly higher parasitaemias than their mission-school counterparts (P=0.010). Of the 31 children (11.9%) found anaemic, 22 (70.4%) had mild anaemia and none had severe anaemia. A significant negative correlation (r=-0.224; P=0.005) was observed between haemoglobin concentration and level of parasitaemia. Infection with Plasmodium appeared to reduce erythrocyte counts (P=0.045), a condition that was exacerbated by co-infection with helminths (P=0.035). Plasma concentrations of total IgE were higher in the children found to be excreting helminth eggs than in those who appeared helminth-free, while levels of anti-P. falciparum IgE were higher in the children with low-grade parasitaemias than in those with more intense parasitaemias. Levels of anti-GPI IgG increased with age and were relatively high in the children who lived at low altitude and in those who were aparasitaemic. The survey results confirm that asymptomatic malarial parasitaemia frequently co-exists with helminth infections in schoolchildren and indicate links with fever, altitude and school type. Immunoglobulin E may play a role in immune protection against helminthiasis whereas anti-GPI antibodies may be important in the development of antimalarial immunity in such children. In Cameroon, as in other areas with endemic malaria, control programmes to reduce the prevalences of infections with intestinal helminths and malarial parasites in schoolchildren, which may effectively reduce the incidence of anaemia, are clearly needed. [ABSTRACT FROM AUTHOR]