Human reticulocytes are one of the fundamental components needed to study the in vitro invasion processes of the human malaria parasite Plasmodium vivax. Additionally examinations of reticulocytes and their binding proteins are difficult in areas of the world that do not have access to advanced equipment or stem cell lines. These issues are particularly relevant to malaria vaccine candidate studies that are directed against surface proteins that the parasites use to gain entry into erythrocytes. Described here is a simple and inexpensive method to increase the reticulocyte count of cord blood samples. Exposure of cord blood to hypotonic saline (0.2%) for 5min selectively lyses the non-reticulocytes resulting in an average 3.6-fold increase in reticulocyte count. Our studies show that this enrichment process does not damage the hemoglobin of the remaining erythrocytes which are still capable of supporting Plasmodium falciparum invasion and growth. This economical and rapid method of enrichment could facilitate studies of in vitro laboratory culturing of other malaria parasite species which preferentially invade reticulocytes such as P. vivax.

Background Aggregated haemozoin crystals within malaria-infected erythrocytes confer susceptibility of parasitized cells to a magnetic field. Here the utility of this method for diagnosis of human malaria is evaluated in a malaria-endemic region of Papua New Guinea (PNG). Methods and findings Individuals with Plasmodium falciparum malaria symptoms (n = 55) provided samples for conventional blood smear (CBS) and magnetic deposition microscopy (MDM) diagnosis. Standard Giemsa staining and light microscopy was performed to evaluate all preparations. Plasmodium falciparum parasitaemia observed on MDM slides was consistently higher than parasitaemia observed by (CBS) for ring (CBS = 2.6 vs. MDM = 3.4%; t-test P-value = 0.13), trophozoite (CBS = 0.5 vs. MDM = 1.6%; t-test P-value = 0.01), schizont (CBS = 0.003 vs. MDM = 0.1%; t-test P-value = 0.08) and gametocyte (CBS = 0.001 vs. MDM = 0.4%; t-test P-value = 0.0002) parasitaemias. Gametocyte prevalence determined by CBS compared to MDM increased from 7.3% to 45%, respectively. Conclusion MDM increased detection sensitivity of P. falciparum -infected, haemozoin-containing erythrocytes from infected humans while maintaining detection of ring-stage parasites. Gametocyte prevalence five-fold higher than observed by CBS suggests higher malaria transmission potential in PNG endemic sites compared to previous estimates.