Measurement of Plasmodium falciparum growth rates in vivo: a test of malaria vaccines
Cheng, Q.; Lawrence, G.; Reed, C.; Stowers, A.; Ranford-Cartwright, L.; Creasey, A.; Carter, R.; Saul, A.
American Journal of Tropical Medicine and Hygiene 57(4): 495-500
1997
ISSN/ISBN: 0002-9637 PMID: 9347970 Document Number: 479479
Several prototype vaccines against the asexual blood stage of malaria are undergoing preclinical and phase I testing, although no practical and sensitive clinical trial procedure has been available for measuring their impact on parasite growth. A system is described that permits parasite growth rates to be measured in volunteers. Two necessary elements of this system were developed: suitable blood-stage Plasmodium falciparum inocula and a highly sensitive and quantitative assay to measure parasite growth during the incubation period. Five non-immune volunteers were infected with an inoculum as small as 300 parasites and it was shown that the resultant in vivo asexual parasite growth rates were reproducible at 12- to 15-fold per cycle. The system allowed the infection to be followed for 8 days before treatment without symptoms developing. The results indicate that it is feasible to directly measure the anti-parasite efficacy of a prototype malaria vaccine in human volunteers without subjecting them to the risk of disease.