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 define d as clinical episodes with fever (body temperature greater than or equal t o 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 regressio n 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 chil dren and adults, and this severity was not correlated with the duration of the pathologic episode. It was not possible to distinguish objectively diff erent malaria attack types according to the severity of clinical manifestat ions. 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 t he first would play a major role as age increases. They suggest also that t he initial clinical presentation of malaria attacks is not predictive of th e level of protective immunity.