Evaluating the Genetic Diversity of Plasmodium ovale curtisi and wallikeri in Coastal Tanzania

In 2023, there were an estimated 263 million cases and 597,000 deaths related to malaria infections caused by Plasmodium parasites. The ongoing transmission of Plasmodium ovale (inclusive of P. ovale curtisi and wallikeri) in several African countries highlights a deficit in malaria control strategies. P. ovale curtisi and P. ovale wallikeri are the only widespread Plasmodium species in Africa capable of causing relapse infections, yet the genetic diversity and epidemiology of these species is largely unknown. This study aimed to develop a method to understand the genetic diversity of P. ovale by using a set of four genetic markers to genotype and assign haplotype profiles or “fingerprints” to 58 genotyped P. ovale isolates identified in a clinical cohort in coastal Tanzania. The genetic diversity of these markers was calculated using a metric of heterozygosity, and the discriminatory power of the genotyping panel was measured using Simpson’s Diversity Index. Of the 52 samples genotyped across these three markers, 48 of 52 samples, or (92.3%) were successfully genotyped in at least one genetic marker, including the identification of 10 multiclonal infections. Additionally, we found heterozygosity ranging from 0.27-0.83 in Poc isolates and 0.88-0.92 in Pow isolates, being broadly more diverse in Pow. After consolidating the microsatellite-specific results, we found high Simpson’s Diversity in both species (0.79 and 1.00 for Poc and Pow, respectively), indicating that this genotyping strategy can effectively “fingerprint” P. ovale isolates from a clinical cohort in coastal Tanzania. These findings are among the first to genotype P. ovale isolates in an endemic population, and this genotyping strategy will be applied to other parasite populations in East Africa to better understand  P. ovale epidemiology and transmission patterns, especially as it relates to relapse dynamics. P. ovale continues to be a persistent malaria species in Sub-Saharan Africa, and these findings contribute to a greater understanding needed to effectively target these species.