Anaemia caused by asymptomatic Plasmodium falciparum infection in semiimmune African schoolchildren

A cohort of 250 Ghanaian schoolchildren aged 5 - 15 years was followed clin ically and parasitologically for 4 months in 1997/98 in order to study the effect of asymptomatic Plasmodium falciparum infections on haematological i ndices and bone-marrow responses. Of the 250 children 65 met the predefined study criteria. Thus, 14 children were parasite-free throughout (group 1), 44 had P. falciparum in all blood samples collected but no symptoms of mal aria (group 2), and 7 had 1 malaria attack during the study period (group 3 ). At the end of the study the mean haemoglobin (Hb) level in group I was 1 23 g/L, significantly higher than the value of 114 g/L in groups 2 and 3 (P < 0 . 02, adjusted for age and splenomegaly). The low Hb in group 2 was as sociated with subnormal plasma iron. Low Hb was associated with elevated er ythropoietin (EPO) levels, and there was a positive correlation between EPO and reticulocyte counts. However, the reticulocyte response to EPO was mor e pronounced in uninfected than in infected children, suggesting a partial interference with erythropoiesis in asymptomatic infections. Children with asymptomatic infections had significantly higher plasma levels of tumour ne crosis factor than uninfected children (geometric means 50 ng/L and 27 ng/L , respectively, P<0 . 001) and this cytokine may contribute to bone-marrow suppression and disturbed iron metabolism. We suggest that asymptomatic mal aria leads to a homeostatic imbalance in which erythrocyte loss due to para site replication is only partially compensated for by increased erythropoie sis. The consequences of the reduced Hb levels on the development and cogni tive abilities of children with asymptomatic infections, and the risk of pr ecipitation of iron deficiency, deserve further study and should be conside red in malaria control programmes that aim at reducing morbidity rather tha n transmission.