The role of low level Plasmodium falciparum parasitaemia in anaemia among infants living in an area of intense and perennial transmission.

Children under one year of age in an area of intense and perennial Plasmodium falciparum transmission were followed up for one year to establish to what extent chronic, low parasitaemia was associated with severe anaemia. There was a significant increase in the prevalence of anaemia (PCV < or = 25%) with increase in parasite density. PCV levels were related not only to concurrent parasite density but also decreased with densities measured one month previously. At any point in time, the mean PCV level in infants with low parasitaemia (< 1000 parasites/microliter) was higher than that of infants with intermediate (1000-9999/microliter) and high parasite densities (> or 10000/microliter). After the age of 7 months, infants with low parasite densities tend to recover, probably as a result of developing immunity. At the age of 12 months, they have similar PCV levels to infants with no detectable parasitaemia by microscopy. The maintenance of low parasite density appears crucial to the survival of infants in malaria endemic areas. The findings suggest that interventions which lower parasite densities in areas of intense transmission reduce the development of severe malarial anaemia and thus malaria-related mortality and morbidity in infants.