Table 1.

Protection against reinfection by exposure to sporozoites under pyrimethamine causal prophylaxis^a

Drug	Initial challenge			Rechallenge
	Time to challenge (days)	No. of animals protected/infected (%)	Prepatencyb (days)	Time to rechallenge (days)	No. of animals protected/infected (%)	Prepatency (days)
Pyrimethamine	35	9/9 (100)c	N/A	130	5/5 (100)	N/A
	64	4/4 (100)	N/A	158	1/4 (25)	(8)
	199	4/4 (100)	N/A
Noned		0/5 (0)	3

^aPyrimethamine was administered orally with the drinking water for 42 h at a concentration of 70 μg/ml to C57BL/6 mice. Animals were immunized three times by intravenous injection of 10,000 sporozoites each time. Boosts were given at 2- to 4-week intervals under oral pyrimethamine. Animals were challenged by intravenous injection of 10,000 sporozoites or by bites from 5 to 10 infectious mosquitoes. Rechallenge was carried out by intravenous injection of 10,000 sporozoites. Animals were monitored for parasitemia for at least 14 days after challenge.

^bDefined as the time to detection of the first blood-stage parasite. N/A, not applicable.

^cIn another experiment, 3 protected animals were challenged with 7,500 infected red blood cells; they developed parasitemia on the same day as the controls (day 5), indicating liver-stage-specific protection of the sporozoite immunization protocol.

^dData for control animals are displayed from combined experiments. For all challenges, age-matched naïve control animals (at least 2) were infected in parallel.