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dc.contributor.authorLee, Kim-Sung
dc.contributor.authorCox Singh, Janet
dc.contributor.authorSingh, Balbir
dc.identifier.citationLee , K-S , Cox Singh , J & Singh , B 2009 , ' Morphological features and differential counts of Plasmodium knowlesi parasites in naturally acquired human infections ' , Malaria Journal , vol. 8 , 73 .
dc.identifier.otherPURE: 23166003
dc.identifier.otherPURE UUID: b6a6899f-03b9-43e9-b0d7-78ac622edd92
dc.identifier.otherWOS: 000266327100001
dc.identifier.otherScopus: 65149103017
dc.identifier.otherORCID: /0000-0003-4878-5188/work/64034440
dc.description.abstractBackground: Human infections with Plasmodium knowlesi, a simian malaria parasite, are more common than previously thought. They have been detected by molecular detection methods in various countries in Southeast Asia, where they were initially diagnosed by microscopy mainly as Plasmodium malariae and at times, as Plasmodium falciparum. There is a paucity of information on the morphology of P. knowlesi parasites and proportion of each erythrocytic stage in naturally acquired human infections. Therefore, detailed descriptions of the morphological characteristics and differential counts of the erythrocytic stages of P. knowlesi parasites in human infections were made, photographs were taken, and morphological features were compared with those of P. malariae and P. falciparum. Methods: Thick and thin blood films were made prior to administration of anti-malarial treatment in patients who were subsequently confirmed as having single species knowlesi infections by PCR assays. Giemsa-stained blood films, prepared from 10 randomly selected patients with a parasitaemia ranging from 610 to 236,000 parasites per mu l blood, were examined. Results: The P. knowlesi infection was highly synchronous in only one patient, where 97% of the parasites were at the late trophozoite stage. Early, late and mature trophozoites and schizonts were observed in films from all patients except three; where schizonts and early trophozoites were absent in two and one patient, respectively. Gametocytes were observed in four patients, comprising only between 1.2 to 2.8% of infected erythrocytes. The early trophozoites of P. knowlesi morphologically resemble those of P. falciparum. The late and mature trophozoites, schizonts and gametocytes appear very similar to those of P. malariae. Careful examinations revealed that some minor morphological differences existed between P. knowlesi and P. malariae. These include trophozoites of knowlesi with double chromatin dots and at times with two or three parasites per erythrocyte and mature schizonts of P. knowlesi having 16 merozoites, compared with 12 for P. malariae. Conclusion: Plasmodium knowlesi infections in humans are not highly synchronous. The morphological resemblance of early trophozoites of P. knowlesi to P. falciparum and later erythrocytic stages to P. malariae makes it extremely difficult to identify P. knowlesi infections by microscopy alone.
dc.relation.ispartofMalaria Journalen
dc.rights© 2009 Lee et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.en
dc.subjectRB Pathologyen
dc.subjectSDG 3 - Good Health and Well-beingen
dc.titleMorphological features and differential counts of Plasmodium knowlesi parasites in naturally acquired human infectionsen
dc.typeJournal articleen
dc.description.versionPublisher PDFen
dc.contributor.institutionUniversity of St Andrews. School of Medicineen
dc.contributor.institutionUniversity of St Andrews. Infection Groupen
dc.contributor.institutionUniversity of St Andrews. Biomedical Sciences Research Complexen
dc.description.statusPeer revieweden

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