Fig. 2

The effect of sporozoite treatment prior to injection. a Sporozoite infectivity is highest when delivered intravenously as compared to subcutaneous (tail, back), intraperitoneal and intramuscular injection. b Luminescence of mice infected with sporozoites isolated on different days of mosquito infection. Data indicate that sporozoites isolated on day 20 of mosquito infection are most infective. Luminescence readings were taken 42 h after mouse infection. The red dotted line indicates the background signal as determined in Fig. 1a. b, c Mouse luminescence of sporozoites dissected in HBSS supplemented with 2% FCS (b) or without FCS (c) and injected at various times after dissection. Dissection in serum provides greater sporozoite infectivity than dissection without serum. Dissecting without serum also results in a time-dependent loss of infectivity. d Comparison of infectivity of fresh sporozoites to sporozoites frozen under various different media compositions. All frozen sporozoites are > 90% less infective than freshly isolated sporozoites. *p < 0.05; **p < 0.01, Mann–Whitney test. Dashed lines represent background bioluminescence levels obtained from uninfected mice injected with luciferin