[Observation on parasite density in the early stage of vivax malaria]

Thirty-eight cases were artificially infected with local Plasmodium vivax sporozoites and experienced onsets of acute attacks after a short incubation period. The parasite densities upon the patent of malaria parasites in the peripheral blood and the primary clinical onset were 0.2-1.6 and 0.6-4 040/microliters, respectively. Such significant difference in parasitaemia level seems to be closely related to the interval between the initial parasitaemia and the first onset, as indicated by the fact that for the majority of cases, the earlier the appearance of clinical attack after sporozoite inoculation, the lower the parasite density at the beginning of the patent period, while primary onsets of later occurrence, in those with higher initial parasitemia. The biological and epidemiological significance of the evidence was discussed.