PLASMODIUM-GALLINACEUM - DENSITY DEPENDENT LIMITS ON INFECTIVITY TO AEDES-AEGYPTI

In acute, blood-induced infections of chickens, the malarial parasite P. gallinaceum is most infective to the mosquito A. aegypti 1 day before gametocyte numbers peak. In an effort to account for this disynchrony, daily changes in parasite infectivity, parasitemia, hematocrit, and Hb were measured during the course of infections. Three events were correlated with the loss of infectivity; in the 24 h between peak infectivity and peak gametocytemia, schizont-induced hemolysis reduced the red blood cell volume 22%. P. gallinaceum zygotes, fertilized in vitro and mixed with heavily infected red blood cells from which all viable, mature gametocytes had been removed, produced 67% fewer oocysts than when combined with uninfected red blood cells. Zygotes fertilized in vitro on the day of peak parasitemia produced 47% fewer oocysts than zygotes prepared 24 h earlier. High parasite density reduces infectiousness by destroying, through hemolysis and intraerythrocytic metabolism, a substance necessary to the sporogonic stages, and that there is also an intrinsic loss of infectivity, possibly due to decreased efficiency of fertilization.