Several methods based on the detection of the parasite-specific pigment haemozoin (Hz) in blood are currently being investigated as alternative diagnostic methods for malaria. Although this approach may appear attractive, the fact that in Plasmodium falciparum (P. f.) malaria, the severity of which should give it the highest diagnostic priority, the fact that most circulating intra-erythrocytic P. f. parasites contain little or no Hz raises some concern. We used flow cytometry to investigate the possibilities and limitations of the detection of intra-erythrocytic Hz in malaria infected patient blood samples and in vitro cultures. However, reliable detection of ring-forms or young trophozoites of P. f. parasites could not be achieved, although one-quarter of mature parasites could be detected after 24-48 h in culture. Our results strongly suggest that, although it may be useful for monitoring maturation, detection of intra-erythrocytic Hz by flow cytometry will not provide an optimal method for diagnosis of P. falciparum malaria.
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