Studies on infections with two strains of Plasmodium inui from Taiwan in rhesus monkeys and different anopheline mosquitoes.

Rhesus monkeys infected with the Taiwan strains of Plasmodium inui could be appropriate models for understanding host-parasite relationships during long-term chronic infection. Two strains of P. inui originally from Taiwan were studied in rhesus monkeys and different anopheline mosquitoes. Maximum parasite counts for 13 intact animals infected with the Taiwan I strain ranged from 22,215 to 760,000/microl (median maximum parasite count = 242,800/microl). Following splenectomy, the maximum parasite count for the 9 animals ranged from 160,000 to 2,360,000/microl (median = 1,160,000/microl). Sporozoite transmission was demonstrated via the bites of infected Anopheles dirus mosquitoes and by the intravenous inoculation of sporozoites harvested from the guts of infected Anopheles maculatus. Prepatent periods were 12 and 20 days, respectively. With monkeys infected with the Taiwan II strain, the parasite counts when intact were from 40,882 to 223,686/microl. After splenectomy, maximum parasite counts ranged from 96,750 to 1,960,000/microl (median maximum parasite count for 8 splenectomized animals = 840,000/microl). Two transmissions were obtained via the bites of infected An. dirus mosquitoes; prepatent periods were 10 days. Limited studies with progressively increasing doses of pyrimethamine resulted in parasites more resistant to treatment.