Large sequence heterogeneity of the small subunit ribosomal RNA gene of Plasmodium ovale in Cambodia

Plasmodium ovale malaria has been reported in various countries in southeast Asia, but never in Cambodia. Using a species-specific polymerase chain reaction (PCR) targeting the small subunit (SSU) ribosomal RNA (rRNA) gene. we detected P. ovals in nearly 4% of the inhabitants of a northeastern Cambodian village. Plasmodium ovale was associated with at least one other Plasmodium species, and two quadruple infections were detected. The diagnosis was confirmed by microscopy and by SSU rRNA PCR product sequencing. The sequences shared 96-99% identity with published sequences, and displayed I substantial heterogeneity with 2-4 different haplotypes per sample. Nine distinct SSU rRNA haplotypes were identified, including seven novel variants. Phylogenetic analysis showed two major genetic clusters. suggesting amplification of two distinct gene sets and/or P. ovale variants from each sample. Our data indicate that P. ovale was overlooked in Cambodia until now, and call for the implementation of larger prevalence surveys and accurate diagnosis methods in this country.