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LOW MULTIPLICATION RATES OF AFRICAN PLASMODIUM FALCIPARUM ISOLATES AND LACK OF ASSOCIATION OF MULTIPLICATION RATE AND RED BLOOD CELL SELECTIVITY WITH MALARIA VIRULENCE

Two potential malaria virulence factors, parasite multiplication rate (PMR) and red blood cell selectivity (measured as selectivity index [SI]), were assessed in Plasmodium falciparum clinical isolates from Mali and Kenya. At both sites, PMRs were low (Kenya median = 2.2, n = 33; Mali median = 2.6, n = 61) and did not differ significantly between uncomplicated and severe malaria cases. Malian isolates from hyperparasitemic patients had significantly lower PMRs (median = 1.8, n = 19) than other Malian isolates (uncomplicated malaria median = 3.1, n = 23; severe malaria median = 2.8, n = 19; P = 0.03, by Kruskal-Wallis test). Selective invasion occurred at both sites (Kenya geometric mean SI = 1.9, n = 98; Mali geometric mean SI = 1.6, n = 104), and there was no significant association between the SI and malaria severity. Therefore, in contrast to previous results from Thailand, we found no association of PMR and SI with malaria severity in African children. This raises the possibility of differences in the mechanisms of malaria virulence between sub-Saharan Africa and Asia.

Received May 30, 2005. Accepted for publication November 14, 2005.

Acknowledgments: We are grateful to the Bandiagara Malaria Project team in Mali and the clinical, nursing, and laboratory staff at the Kenya Medical Research Unit in Kilifi for their assistance with this study, and to the patients and their parents at both study sites. We are also grateful to Andrew Read, David Conway, and Susana Nery for discussions and comments on the manuscript. This work is published with the permission of the director of the Kenya Medical Research Institute.

Financial support: This work was supported by the Wellcome Trust (PhD studentship to Anne-Marie Deans and a Senior Research Fellowship to J. Alexandra Rowe, grant no. 067431) and the National Institutes of Health (contract no. N01-AI-85346).

Disclosure: None of the authors have commercial or other associations that might pose a conflict of interest.

^* Address correspondence to J. Alexandra Rowe, Institute of Immunology and Infection Research, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JT, United Kingdom. E-mail: Alex.Rowe{at}ed.ac.uk

Authors’ addresses: Anne-Marie Deans, Ahmed Raza and J. Alexandra Rowe, Institute of Immunology and Infection Research, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JT, United Kingdom, Telephone: 44-131-650-5492, Fax: 44-131-650-6564, e-mail: Alex.Rowe{at}ed.ac.uk. Kirsten E. Lyke and Christopher V. Plowe, Malaria Section, Center for Vaccine Development, University of Maryland School of Medicine, 685 West Baltimore Street, HSF1-480, Baltimore MD 21201, Fax: 410-706-6205. Mahamadou A. Thera, Abdoulaye Kone, and Ogobara K. Doumbo, Malaria Research and Training Center, Département d’Epidémiologie des Affections Parasitaires, Faculté de Médecine de Pharmacie et d’Odonto-Stomatologie, BP 1805 Bamako, Mali, Telephone/Fax: 223-222-8109. Oscar Kai and Kevin Marsh, Kenya Medical Research Institute/Wellcome Trust Collaborative Program, PO Box 230, 80108, Kilifi, Kenya, Fax: 254-125-22390. Margaret J. Mackinnon, Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, United Kingdom, Fax: 44-1223-333-346.

Reprint requests: J. Alexandra Rowe, Institute of Immunology and Infection Research, University of Edinburgh, West Mains Road, Ed-inburgh, EH9 3JT, United Kingdom.

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