Seasonal Variation and Interspecies Dynamics Among Plasmodium falciparum and ovale Species in Bagamoyo, Tanzania.

BACKGROUND

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 parts of East Africa.

METHODS

We conducted polymerase chain reaction (PCR)-based screening of 7173 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.

RESULTS

Plasmodium falciparum 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%). P. ovale 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.

CONCLUSIONS

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.