Parasitological correlates of Plasmodium ovale curtisi and Plasmodium ovale wallikeri infection.
Malaria, due to Plasmodium ovale, can be challenging to diagnose due to clinically mild disease and low parasite burden. Two genetically distinct sub-species of P. ovale exist: Plasmodium ovale curtisi (classic) and Plasmodium ovale wallikeri (variant). It is presently unknown if the sub-species causing infection affects performance of malaria diagnostic tests. The aim of this work was to understand how the genetically distinct sub-species, P. o. curtisi and P. o. wallikeri, affect malaria diagnostic tests.



Plasmodium ovale-positive whole blood specimens were sub-speciated by PCR and sequencing of 18S rRNA and dhfr-ts. Parasitaemia, morphology, pan-aldolase positivity, 18S copy number, and dhfr-ts sequences were compared between sub-species.



From 2006 to 2015, 49 P. ovale isolates were identified, of which 22 were P. o. curtisi and 27 P. o. wallikeri; 80% were identified in the last five years, and 88% were acquired in West Africa. Sub-species did not differ by parasitaemia, 18S copy number, or pan-aldolase positivity. Lack of Schüffner's stippling was over-represented among P. o. wallikeri isolates (p = 0.02). Several nucleotide polymorphisms between the sub-species were observed, but they do not occur at sites believed to relate to antifolate binding.



Plasmodium ovale is increasing among travellers to West Africa, although sub-species do not differ significantly by parasitologic features such as parasitaemia. Absence of Schüffner's stippling may be a feature specific to P. o. wallikeri and is a novel finding.
McMaster University, Hamilton, Canada.
Melissa S
MS
Phuong
Public Health Ontario Laboratories, Toronto, Canada.
Rachel
R
Lau
Public Health Ontario Laboratories, Toronto, Canada.
Filip
F
Ralevski
Public Health Ontario Laboratories, Toronto, Canada. andrea.boggild@utoronto.ca.|Tropical Disease Unit, Division of Infectious Diseases, Toronto General Hospital, University Health Network, 200 Elizabeth Street, 13EN-218, Toronto, ON, M5G 2C4, Canada. andrea.boggild@utoronto.ca.|University of Toronto, Toronto, Canada. andrea.boggild@utoronto.ca.
Andrea K
AK
Boggild
D000354:Africa, Western; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D003955:Diagnostic Tests, Routine / Q000379:methods*; D005634:Fructose-Bisphosphate Aldolase / Q000032:analysis; D006801:Humans; D008288:Malaria / Q000175:diagnosis* / Q000469:parasitology* / Q000473:pathology; D059208:Parasite Load; D018512:Parasitemia / Q000469:parasitology; D041122:Plasmodium ovale / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D016133:Polymerase Chain Reaction; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D017422:Sequence Analysis, DNA
D016054:DNA, Protozoan; D004275:DNA, Ribosomal; D012337:RNA, Ribosomal, 18S; D005634:Fructose-Bisphosphate Aldolase
Malaria diagnosis; Microscopy; PCR; Plasmodium ovale; Rapid antigen detection test