Plasmodium ovale in Bangladesh: genetic diversity and the first known evidence of the sympatric distribution of Plasmodium ovale curtisi and Plasmodium ovale wallikeri in southern Asia

In spite of the high prevalence of malaria in Bangladesh and other southern Asian countries, there remains a substantial shortage of knowledge about the less common human malaria parasites. Recent studies indicate that Plasmodium ovale is made up of two species, namely Plasmodium ovale wallikeri and Plasmodium ovale curtisi. Genus- and species-specific nested PCR analyses of the ssrRNA gene was used to detect P. ovale infections among 2,246 diagnostic samples. Plasmodium ovale infections were further differentiated by nested PCR of the potra gene and multilocus sequence analysis of the cox1, porbp2 and the ssrRNA genes. Both P. ovale curtisi and P. ovale wallikeri occur sympatrically in the Chittagong Hill Tracts, Bangladesh and all patients presented with a mild or asymptomatic symptom complex at the time of diagnosis. The pathogens can be differentiated by nested PCRs targeting the ssrRNA and potra genes, and display dimorphism in multilocus sequence analyses. We believe that we report the first evidence of sympatric P. ovale curtisi and P. ovale wallikeri in southern Asia within a relatively confined study area of less than 5,000 km(2). High rates of mixed infections, the emergence of "new" human malaria parasite species and the evidence of zoonotic capability call for optimised diagnostic strategies for a new era of eradication.