Abstract
BackgroundTo assess the occurrence of Plasmodium ovale wallikeri and Plasmodium ovale curtisi species in travellers returning to Germany, two real-time PCR protocols for the detection and differentiation of the two P. ovale species were compared. Results of parasite differentiation were correlated with patient data.MethodsResidual nucleic acid extractions from EDTA blood samples of patients with P. ovale spp. malaria, collected between 2010 and 2019 at the National Reference Centre for Tropical Pathogens in Germany, were subjected to further parasite discrimination in a retrospective assessment. All samples had been analysed by microscopy and by P. ovale spp.-specific real-time PCR without discrimination on species level. Two different real-time PCR protocols for species discrimination of P. o. curtisi and P. o. wallikeri were carried out. Results were correlated with patient data on gender, age, travel destination, thrombocyte count, and duration of parasite latency.ResultsSamples from 77 P. ovale spp. malaria patients were assessed, with a male:female ratio of about 2:1 and a median age of 30 years. Parasitaemia was low, ranging from few visible parasites up to 1% infected erythrocytes. Discriminative real-time PCRs revealed 41 cases of P. o. curtisi and 36 cases of P. o. wallikeri infections. Concordance of results by the two PCR approaches was 100%. Assessment of travel destinations confirmed co-existence of P. o. curtisi and P. o. wallikeri over a wide range of countries in sub-Saharan Africa. Latency periods for the two P. ovale species were similar, with median values of 56.0 days for P. o. curtisi and 58.0 days for P. o. wallikeri; likewise, there was no statistically significant difference in thrombocyte count with median values of 138.5/µL for patients with P. o. curtisi and 152.0/µL for P. o. wallikeri-infected patients.ConclusionsTwo different real-time PCR protocols were found to be suitable for the discrimination of P. o. curtisi and P. o. wallikeri with only minor differences in sensitivity. Due to the overall low parasitaemia and the lack of differences in severity-related aspects like parasite latency periods or thrombocyte counts, this study supports the use of P. ovale spp. PCR without discrimination on species level to confirm the diagnosis and to inform clinical management of malaria in these patients.
Highlights
To assess the occurrence of Plasmodium ovale wallikeri and Plasmodium ovale curtisi species in travellers returning to Germany, two real-time polymerase chain reaction (PCR) protocols for the detection and differentiation of the two P. ovale species were compared
Design, and setting The epidemiology of P. o. curtisi and P. o. wallikeri in travellers returning to Germany and the available patientrelated information were assessed in a retrospective cross-sectional study over 10 years using clinical information and residual sample materials collected at the Bernhard Nocht Institute for Tropical Medicine Hamburg, the German National Reference for Tropical Pathogens, between 2010 and 2019
Range of parasitaemia in microscopically positive samples Cycle threshold (Ct) values of the P. ovale curtisi PCR according to Bauffe et al Ct values of the P. ovale curtisi PCR according to Calderaro et al Ct values of the P. ovale wallikeri PCR according to Bauffe et al Ct values of the P. ovale wallikeri PCR according to Calderaro et al interquartile ranges (IQR) = interquartile range
Summary
To assess the occurrence of Plasmodium ovale wallikeri and Plasmodium ovale curtisi species in travellers returning to Germany, two real-time PCR protocols for the detection and differentiation of the two P. ovale species were compared. Human Plasmodium ovale spp. malaria is caused by two different sympatric Plasmodium species, namely P. ovale curtisi, which was considered the “classic” human pathogen, and P. ovale wallikeri, which has been described as a genetically distinguishable variant. A wide range of sub-Saharan Africa has been identified as the major region of P. ovale spp. acquisition for Chinese travellers [8, 9, 11, 12], while a majority (88%) of returnees to Canada came from Western Africa [1] Both P. ovale spp. have been infrequently reported from Bangladesh [16]; Bioko Island [17], the Comoros Islands [18], Congo-Brazzaville [17], Ethiopia [19, 20], Ghana [21], India [22], the Ivory Coast [16], Kenya [23], Senegal [24, 25], and Uganda [17]. P. o. wallikeri has been detected both in human patients and in Western Lowland gorillas in the Central African Republic [28]
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