Age- and species-specific duration of infection in asymptomatic malaria infections in Papua New Guinea

The burden and duration of asymptomatic malaria infections were measured in residents of the malaria endemic village of Gonoa, Madang Province, Papua New Guinea. Plasmodium falciparum, P. vivax and P. malariae infections in p eople aged 4 years to adulthood were compared. Frequent sampling at 3-day i ntervals for up to 61 days allowed assessment of individual episodes of inf ection. Statistical assessment of P. falciparum detection revealed a period icity consistent with synchronous replication of this species over periods up to 27 days. The duration of P. falciparum episodes was longer across all age groups than that of P. vivax and P. malariae. A trend for decreasing d uration with age was also noted in data from each species. This was most pr ominent in P. falciparum infections: median duration in 4-year-olds was > 4 8 days compared with a median between 9 and 15 days in older children and a dults. The results are consistent with the slow acquisition of immunity to antigenically diverse Plasmodium populations and suggest a faster rate of a cquisition to P. vivax and P. malariae than to P. falciparum.