Plasmodium falciparum clinical malaria in Dielmo, a holoendemic area in Senegal: no influence of acquired immunity on initial symptomatology and severity of malaria attacks.

Six hundred eighty-nine Plasmodium falciparum malaria attacks were observed during a three-year period among 226 inhabitants of the village of Dielmo, Senegal, an area of high malaria transmission. Malaria attacks were defined as clinical episodes with fever (body temperature > or = 38.0 degrees C) or reporting of fever or headache or vomiting, associated with a parasite:leukocyte ratio above an age-dependent pyrogenic threshold identified in this population. The symptom frequencies were tested against age, gender, and parasite density using a random-effect logistic regression model and the study of distinguishable clinical presentations was carried out by multi-correspondence analysis. There was little difference between the severity of symptoms during the initial course of attacks in young children and adults, and this severity was not correlated with the duration of the pathologic episode. It was not possible to distinguish objectively different malaria attack types according to the severity of clinical manifestations. In contrast, the duration of fever, symptoms, and parasite clearance were significantly longer among the youngest children than among the oldest children and adults. These findings suggest that of the two components of protective immunity, anti-parasite immunity and anti-toxic immunity, only the first would play a major role as age increases. They suggest also that the initial clinical presentation of malaria attacks is not predictive of the level of protective immunity.