ABO-blood-group types and protection against severe, Plasmodium falciparum malaria S. L. PATHIRANA*, H. K. ALLES*, S. BANDARA { , M. PHONE-KYAW*, M. K. PERERA*, A. R. WICKREMASINGHE { , K. N. MENDIS* and S. M. HANDUNNETTI* *Malaria Research Unit, Department of Parasitology, Faculty of Medicine, University of Colombo, P.O. Box 271, Colombo, Sri Lanka { Malaria Unit Clinical Laboratory, General Hospital, Anuradhapura, Sri Lanka { Department of Community Medicine and Family Medicine, Faculty of Medical Sciences, University of Kelaniya, Ragama, Kelaniya, Sri Lanka Received 7 October 2004, Revised 15 November 2004, Accepted 17 November 2004 Although the ABO blood group of the human host has been reported to influence malarial infection, there have been few clinical observations on this effect. A hospital-based, comparative study was therefore performed to investigate the relationship between blood-group type and severe disease in Plasmodium falciparum malaria. Overall, 243 cases of malaria (163 uncomplicated and 80 severe) and 65 patients with severe, non-malarial infections were studied. In terms of ABO-blood-group composition, the patients with severe malaria were significantly different from the patients with the uncomplicated disease (P,0.001) and also from a population control described previously (P,0.0001). The patients with uncomplicated malaria or severe but non-malarial disease were, however, similar to the population control. The cases of severe malaria were significantly less likely to be of blood group O (P50.0003), and significantly more likely to be of group AB (P,0.0001), than the patients with non- severe malaria. It appears that individuals who are of blood-group O are relatively resistant to the severe disease caused by P. falciparum infection. During studies on the innate resistance of humans to some parasites, several host genes have been shown to be associated with either increased or decreased suscept- ibility to malarial infection and/or to severe and complicated malaria. In West Africa, for example, two leucocyte antigens — the class-I antigen Bw53 and the class-II anti- gen DRB1* 1302 — have been found to be independently associated with protection from severe, Plasmodium falciparum malaria (Hill et al., 1991). Conversely, McGuire et al. (1994) found the presence of a particular allele of the gene for tumour necrosis factor-a — TNFa*2 — to be associated with susceptibility to cerebral malaria, at least in The Gambia. The results of the study by Wattavidanage et al. (1999) indicated that Sri Lankans with severe malaria were also particularly likely to be carrying the TNFa*2 allele (albeit mainly in the heterozygous state). Certain red-cell polymorphisms, such as alpha-thalassaemia, render individuals more susceptible to uncomplicated malaria (Williams et al., 1996) but in Africa the haemoglobin variants HbC and HbS are associated with high levels of protection against severe malaria (Agarwal et al., 2000; Weatherall et al., 2002). In Kenya at least, the O blood group appears to confer some protection against cerebral malaria (Rowe et al., 1995). The aim of the present study was to determine which, if any, of the ABO- blood-group types is associated with resis- tance or susceptibility to severe disease in Reprint requests to: S. L. Pathirana. E-mail: slpathirana@sltnet.lk; fax: z94 11 2699284. Annals of Tropical Medicine & Parasitology, Vol. 99, No. 2, 119–124 (2005) # 2005 The Liverpool School of Tropical Medicine DOI: 10.1179/136485905X19946