Background: Plasmodium falciparum infections lead to febrile illness unless the host has sufficient immunity, in which case infection may cause no immediate symptoms (i.e. “asymptomatic parasitaemia”). Previous studies are conflicting on the role of asymptomatic parasitemia in determining the risk of developing febrile malaria. Methods: We monitored 2,513 children living in Kilifi (Kenyan Coast) with blood smears in 17 cross-sectional surveys to identify asymptomatic parasitemia and used active surveillance over 11,325 child-years of follow up to detect febrile malaria. We evaluated the interaction between transmission intensity, age and asymptomatic parasitaemia in determining the risk of developing febrile malaria. Results: In the moderate and high transmission intensity settings, asymptomatic parasitaemia was associated with a reduced risk of febrile malaria in older children (> 3 years), while in the lower transmission setting, asymptomatic parasitaemia was associated with an increased risk of febrile malaria in children of all ages. Additionally, the risk associated with asymptomatic parasitaemia was limited to the first 90 days of follow up. Conclusions: Asymptomatic parasitaemia is modified by transmission intensity and age, altering the risk of developing febrile episodes and suggesting that host immunity plays a prominent role in mediating this process.
Wamae, K., Wambua, J., Nyangweso, G., Mwambingu, G., Osier, F., Ndung’u, F., Bejon, P., Ochola-Oyier, L.I.