title: An observational study of malaria in British travellers: Plasmodium ovale wallikeri and Plasmodium ovale curtisi differ significantly in the duration of latency.
abstract: OBJECTIVE
  Ovale 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.
  
  
  METHODS
  PCR 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.
  
  
  METHODS
  UK National Reference Laboratory.
  
  
  METHODS
  None. 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.
  
  
  RESULTS
  None.
  
  
  RESULTS
  No 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).
  
  
  CONCLUSIONS
  These 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.
authors.affiliation: Public Health England (formerly HPA), Malaria Reference Laboratory, Faculty of Infectious & Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK.
authors.forename: Debbie
authors.initials: D
authors.lastname: Nolder
authors.forename: Mary C
authors.initials: MC
authors.lastname: Oguike
authors.forename: Hector
authors.initials: H
authors.lastname: Maxwell-Scott
authors.forename: Hatoon A
authors.initials: HA
authors.lastname: Niyazi
authors.forename: Valerie
authors.initials: V
authors.lastname: Smith
authors.forename: Peter L
authors.initials: PL
authors.lastname: Chiodini
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Sutherland
keywords: Parasitology