Plasmodium ovale curtisi and Plasmodium ovale wallikeri circulate simultaneously in African communities

Mathieu Ndounga,Teun Bousema,Martha Betson,Kazuyuki Tanabe,J Russell Stothard,Mary Chiaka Oguike,Edward Ntege,Richard Culleton,Immo Kleinschmidt,Carla Proietti,Colin J Sutherland,Martina Burke,Debbie Nolder

doi:10.1016/j.ijpara.2011.01.004

Abstract

It has been proposed that ovale malaria in humans is caused by two closely related but distinct species of malaria parasite, Plasmodium ovale curtisi and Plasmodium ovale wallikeri. It was recently shown that these two parasite types are sympatric at the country level. However, it remains possible that localised geographic, temporal or ecological barriers exist within endemic countries which prevent recombination between the genomes of the two species. Here, using conventional and real-time quantitative PCR (qPCR) methods specifically designed to discriminate P. o. curtisi and P. o. wallikeri, it is shown that both species are present among clinic attendees in Congo-Brazzaville, and occur simultaneously both in lake-side and inland districts in Uganda and on Bioko Island, Equatorial Guinea. Thus P. o. curtisi and P. o. wallikeri in these localities are exactly sympatric in both time and space. These findings are consistent with the existence of a biological barrier, rather than geographical or ecological factors, preventing recombination between P. o. curtisi and P. o. wallikeri. In cross-sectional surveys carried out in Uganda and Bioko, our results show that infections with P. ovale spp. are more common than previously thought, occurring at a frequency of 1–6% in population samples, with both proposed species contributing to ovale malaria in six sites. Malaria elimination programmes in Africa need to include strategies for control of P. o. curtisi and P. o. wallikeri.

Highlights

The human malaria agent Plasmodium ovale was described by Stevens in 1922
In a study of P. ovale conducted by researchers from Mahidol University, Bangkok, and the UK Malaria Reference Laboratory (UKMRL), London, polymorphisms in six loci were examined in 55 isolates
This study has extended previous reports of sympatry between the proposed species P. o. curtisi and P. o. wallikeri (Sutherland et al, 2010) to the Republic of Congo, Equatorial Guinea and specific locations in three regions of Uganda

Summary

Introduction

The human malaria agent Plasmodium ovale was described by Stevens in 1922. Since that time, relatively little attention has been paid to ovale malaria, which is considered to be uncommon, mild in clinical presentation and treated with the conventional antimalarial drug chloroquine (Mueller et al, 2007). Sequencing of rRNA genes from two well-characterised isolates of P. ovale first prompted the suggestion that this species was dimorphic, and raised the possibility that two sub-species might exist (Li et al, 1995). P. ovale dimorphism was proposed to reflect the existence of two fully distinct ovale malaria species, which were unexpectedly shown to be broadly sympatric, at the country level, in both Africa and Asia (Sutherland et al, 2010). These two proposed species have been named Plasmodium ovale curtisi and Plasmodium ovale wallikeri

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Results

Conclusion