Seasonal variation and interspecies dynamics among Plasmodium falciparum and ovale species in Bagamoyo, Tanzania.

Malaria control in sub-Saharan Africa is typically focused on Plasmodium falciparum ( Pf ), but non-falciparum species like P. ovale curtisi ( Poc ) and P. ovale wallikeri ( Pow ) appear to be rising in prevalence, especially in East Africa. We conducted polymerase chain reaction (PCR)-based screening of 7,173 asymptomatic individuals over 5 years of age in coastal Tanzania from 2018-2022, employing real-time 18S rRNA PCR assays for P. falciparum and P. ovale , followed by Poc / Pow detection. Plasmodium positivity was compared across seasons and demographic groups, and interactions between species were analyzed via binomial regression. Pf infection (prevalence 27.4%) was associated with younger age, male sex, and higher recent cumulative rainfall, whereas these associations were not apparent for P. ovale ( Po , prevalence 11.5%). Po infections appeared to peak during months with lower Pf prevalence, especially during the long wet season, when Po mono-infections predominated and fewer Pf - Po co-infections were detected than expected by independent assortment. This apparent antagonism was reversed during the short wet season: Pf - Po co-infections were comparatively enriched despite low overall Po prevalence. In contrast, excess mixed Poc / Pow infections were detected across all seasons, composing 23% of the Po -positive isolates in which a specific Po species could be detected. The epidemiology of P. ovale species in coastal Tanzania suggests they are frequently present when P. falciparum recedes, but also co-infect the same hosts during the short wet season. Meanwhile, the individual Poc and Pow species often co-exist within individuals, perhaps due to co-transmission or concurrent relapse.