Abstract: AIM:To observe the effect of dihydro qinghaosu (DQHS) on the development of Plasmodium yoelii yoelii in Anopheles stephensi and to explore the possibility of whether DQHS has preventive effect against malaria.METHODS: Plasmodium yoelii yoelii infected mice that had been administered with a single dose of different dosages (60 mg/kg,120 mg/kg,180 mg/kg and 240 mg/kg) of DQHS were exposed to mosquitoes to suck blood .The development of malaria parasites in the mosquitoes of the control group and the treated group were observed by light microscopy (LM ) and transmission electron microscopy (TEM ). RESULTS: DQHS exhibited certain inhibitory effect on the infectivity of gametocyte. The degree of inhibition was related to the developmental stages of gametocyte and the drug dosage. Immature gametocytes were more sensitive to DQHS than the mature gametocytes. With the increases in dosage , the positive rate and the den ity of oocyst and sporozoite decreased. However, the difference in the density of sporozoite between 180 mg/kg and 240 mg/kg treated groups was in significant. TEM result showed damage of the membrane system and vacuolation in the cytoplasm of the oocysts (12- 13 d) on mosquito midgut of 60 mg/kg 16 h treated group. The oocysts in the mosquitoes continued to develop after treated with 120 mg/kg of DQHS for 16 h on 3-day-in star. There was no significant difference (P >0.05 ) in the density of oocyst and sporozoite between the control group and the treated group. CONCLUSION:DQHS can affect the infectivity of gametocyte and decrease themalaria transmission but cannot inhibit the sorogonic stage directly.

Key words: Dihydroqinghaosu, Plasmodium yoelii yoelii, infectivity of gametocyte, Anopheles stephensi, sprorogonic stage