Comparative evaluation of methods of malaria parasite density determination in blood samples from patients & experimental animals

Three methods for the quantitation of parasitaemia in malaria were compared with the standard method for ascertaining the accuracy in patients, Plasmo dium berghei infected mice and P. knowlesi infected Rhesus monkeys. Techniq ue I, where parasitaemia was calculated from the number of PRBCs in 10,000 RBCs in thin blood film and the total RBC count of the host, was used as th e standard. Technique II, where parasitaemia was calculated based on the nu mber of PRBCs per WBC and average total WBC count (8000/mu l), was least ac curate. Technique IV, where parasitaemia was calculated from the number of PRBCs per oil immersion field (OIF) of microscope and the estimated amount of blood in one OIF of a thick smear, was most accurate when parasitaemia w as low as in malaria patients and experimental animals with <1 per cent par asitaemia. In mice with moderate parasitaemia (5-10%) and in falciparum mal aria cases (with 3-7% parasitaemia) also technique IV was most accurate. In both animal models showing high (15-25%) and in monkeys with moderate para sitaemia, technique III based on the number of PRBCs per WBC and actual tot al WBC count, was the most accurate. Thus, technique IV being simpler and c ost effective, with standardization of the amount of blood used in making a thick smear, may be used routinely for quantitation of parasitaemia.