Demographic characteristics of the study participants, challenge infective dose, pre-patent period and parasite density after challenge.

Most volunteers were men (63%) and ages ranged between 19–38 years old. No significant differences were observed in the pre-patent period of both groups after the infectious challenge with 2-4 bites of infected mosquitoes. aNumber of infected mosquitoes fed on the arm of volunteer; bPre-patent period defined by positive thick blood smear (TBS); cparasitemia measured at the pre-patent day; dOnset of any symptom, usually weakness or malaise; eNo pre-patent period could be determined as the volunteer remained negative for malaria by TBS during the duration of the study. f no symptoms were reported for those volunteers. NA: Not applicable.