An observational study of malaria in British travellers:Plasmodium ovale wallikeriandPlasmodium ovale curtisidiffer significantly in the duration of latency

Abstract

ObjectivesOvale malaria is caused by two closely related species of protozoan parasite: Plasmodium ovale curtisi and Plasmodium ovale wallikeri Although clearly distinct genetically, there have been no studies comparing the morphology, life cycle or epidemiology of these parasites. We tested the hypothesis that the two species differ in the duration of latency prior to presentation with symptoms of blood-stage infection.DesignPCR was used to identify P ovale curtisi and P ovale wallikeri infections among archived blood from UK malaria patients. Latency periods, estimated as the time between entry into the UK and diagnosis of malaria, were compared between the two groups.SettingUK National Reference Laboratory.ParticipantsNone. Archived parasite material and surveillance data for 74 P ovale curtisi and 60 P ovale wallikeri infections were analysed. Additional epidemiological data were taken from a database of 1045 imported cases.OutcomesNone.ResultsNo differences between the two species were identified by a detailed comparison of parasite morphology (N=9, N=8, respectively) and sex ratio (N=5, N=4) in archived blood films. The geometric mean latency period in P ovale wallikeri was 40.6 days (95% CI 28.9 to 57.0), whereas that for P ovale curtisi was more than twice as long at 85.7 days (95% CI 66.1 to 111.1; p=0.002). Further, the proportion of ovale malaria sensu lato which occurred in patients reporting chemoprophylaxis use was higher than for Plasmodium falciparum (OR 7.56; p<0.0001) or P vivax (OR 1.82; p<0.0001).ConclusionsThese findings provide the first difference of epidemiological significance observed between the two parasites which cause ovale malaria, and suggest that control measures aimed at P falciparum may not be adequate for reducing the burden of malaria caused by P ovale curtisi and P ovale wallikeri.

Sequence-Based Optimization of a Quantitative Real-Time PCR Assay for Detection of Plasmodium ovale and Plasmodium malariae

“…With the recognition of 2 subspecies of P. ovale, both of which were imported to Ontario over our enrollment period, using a diagnostic assay that can reliably detect both strains is imperative to appropriate clinical management (6). In addition, using an assay that can distinguish the 2 subspecies may become epidemiologically important as well, given new published information regarding their differing latencies (12).…”

Recent Advances in Detection of Plasmodium ovale: Implications of Separation into the Two Species Plasmodium ovale wallikeri and Plasmodium ovale curtisi

“…Both species are known to occur sympatrically in Africa and Asia, and even simultaneous infections with both parasites have been reported (6). The two species are indistinguishable by microscopy but seem to differ in their duration of latency (7).…”

Medical Parasitology Taxonomy Update: January 2012 to December 2015

“…Similarly, Parastrongylus (previously Angiostrongylus) mackerrasae and P. cantonensis share highly similar genetic identities and comparable pathogenesis in murine and guinea pig models (12,13). Due to the ongoing controversies surrounding these species, they have The latency period may be longer in P. ovale curtisi than P. ovale wallikeri (15).…”

“…Currently, the Centers for Disease Control and Prevention (CDC) has not fully acknowledged the two distinct strains of P. ovale as causes of human malaria (http:// www.cdc.gov/dpdx/malaria/index.html). They are described as being indistinguishable by microscopy but may differ clinically in their duration of latency (15). PCR-based methods for the detection of P. ovale may be designed to either detect both strains simultaneously or further differentiate the two strains (16).…”