EXPERIMENTAL AND FIELD STUDIES ON SOME BIOLOGICAL CHARACTERISTICS OF PLASMODIUM-VIVAX ISOLATED FROM TROPICAL AND TEMPERATE ZONES OF CHINA

Objective. To clarify some biological behaviors of Plasmodium vivax in cluding the periodical infectivity of gametocytes for mosquitoes, the prepatent period, the incubation period, the relapse patterns and thei r relationship. Methods. Laboratory reared Anopheles sinensis were fed through fetal membrane on blood from patients naturally infected with vivax malaria. After feeding at different hours, the engorged mosquit oes kept in the insectarium were dissected 5-7 days later. The percent age of mosquitoes infected and the mean number of oocysts per gut were taken as criteria of the viability of the gametocytes. The healthy vo lunteers artificially infected by mosquito bite or quantitative inocul ation of sporozoites were treated with 1.5 g chloroquine base alone be fore and after the first and subsequent onset of fever to detect the n atural course of disease in human body. Results. The infection in mosq uitoes can readily be divided into upward, peak, downward and non-infe ctive period. The infectivity reached a peak at interschizogony period and fell to low level at the time when schizogony occurred. The short incubation period was frequently observed in persons bitten by 10 inf ected mosquitoes or 10 000 sporozoites inoculated and the long incubat ion period was constantly recorded in cases receiving 100 sporozoites. When one mosquito was allowed to feed on volunteers or 1000 sporozoit es were injected, the incubation period may be short or prolonged. Con clusions. The 48-hour cycle in the infectivity of gametocyte for mosqu itoes was demonstrated and the peak of oocyst production preceded the peak of parasitaemia by 1 to 3 days. Prompt radical treatment is extra important. Since the incubation period is variable depending on the n umber of sporozoites inoculated and the tropical versus temperate zone malaria is not all-inclusive, the classification of tertian malaria m ight be reconsidered.