Molecular Detection of Plasmodium ovale in Coastal Tanzania

Despite immense progress, malaria continues to be a persistent global health challenge that demands continued attention and resources. Because of increased control efforts, parts of coastal Tanzania have experienced a decline in transmission of Plasmodium falciparum, the dominant malaria species. However, there is little known about the epidemiology of non-falciparum species, which appear to be increasing in prevalence in areas where Plasmodium falciparum is declining. Plasmodium ovale (Po) infections are endemic in parts of sub-Saharan Africa and Southeast Asia and continue to persist via an asymptomatic reservoir. Plasmodium ovale wallikeri (Pow) and Plasmodium ovale curtisi (Poc) are two distinct Plasmodium ovale (Po) species, which tend to go undetected through traditional screening tests due to their natural low parasitemia. To learn of any differences between the epidemiology and prevalence of these distinct species, we investigated the distribution of Po species in Bagamoyo, Tanzania, and their association with demographic and ecological factors including age, sex, geographical region, rainy or dry season, and Plasmodium falciparum coinfection. DNA extracted from blood spots of asymptomatic participants were screened for the presence of Plasmodium ovale parasitemia. Those that were positive were further analyzed using a species-specific real-time qPCR assay which classified Plasmodium ovale-positive isolates as Plasmodium ovale curtisi or wallikeri mono- or coinfections with both Po species (“mixed infections”). Of 550 samples tested, 396 (72%) had successful amplification for at least one Plasmodium ovale species. Plasmodium ovale curtisi dominated, occuring in 65% of these infections and was the more abundant species in 75% of mixed infections. Across all Po infections, 20% were also coinfected with Plasmodium falciparum. The distribution of each Po species was not significantly different by age, sex, seasonality, geography, or Plasmodium falciparum coinfection. These findings are valuable in understanding barriers to malaria elimination in regions where Plasmodium falciparum and Plasmodium ovale are present.