Studies on malarial sporozoites. I. Effect of various environmental conditions

Abstract

Data are presented on the infectivity of sporozoites of P. gallinaceum under various conditions. Mosquitoes exposed to ether in excess or to temperatures below freezing showed drastic reduction of infectivity. Considerable exposure to tobacco smoke, DDT or pyrethrum, minimal exposure to ether, or chilling at temperatures above freezing were apparently harmless to sporozoites. Saline solutions of 0.21, 0.43 and 0.85% were injurious to sporozoites. In the presence of 4.5% blood 0.85% saline was less deleterious than more or less concentrated saline solutions. Heparinized chick blood, plasma, or serum inactivated at 56 °C for 30 minutes were good media, allowing prolonged survival of sporozoites. Normal serum slightly but definitely reduced infectivity. Temperatures up to 21 °C allowed nearly quantitative survival of sporozoites for 3–4 hours. Temperatures of 26 °C or higher markedly reduced infectivity within this period. Intravenous inoculation of sporozoites gave regular, intense infections. Intrahepatic injection was apparently nearly as good. Intramuscular, subcutaneous, and intraperitoneal inoculations resulted in irregular infections of mostly prolonged incubation period. Inoculations by stomach tube were negative. One of four orally inoculated chicks became infected with a prolonged prepatent period. A convenient method is described for routine quantitative induction of infection with sporozoites of Plasmodium gallinaceum.