Quantitative Bioluminescent Imaging of Pre-Erythrocytic Malaria Parasite Infection Using Luciferase-Expressing <i>Plasmodium yoelii</i>

<div><p>The liver stages of <i>Plasmodium</i> parasites are important targets for the development of anti-malarial vaccine candidates and chemoprophylaxis approaches that aim to prevent clinical infection. Analyzing the impact of interventions on liver stages in the murine malaria model system <i>Plasmodium yoelii</i> has been cumbersome and requires terminal procedures. <i>In vivo</i> imaging of bioluminescent parasites has previously been shown to be an effective and non-invasive alternative to monitoring liver stage burden in the <i>Plasmodium berghei</i> model. Here we report the generation and characterization of a transgenic <i>P. yoelii</i> parasite expressing the reporter protein luciferase throughout the parasite life cycle. <i>In vivo</i> bioluminescent imaging of these parasites allows for quantitative analysis of <i>P. yoelii</i> liver stage burden and parasite development, which is comparable to quantitative RT-PCR analysis of liver infection. Using this system, we show that both BALB/cJ and C57BL/6 mice show comparable susceptibility to <i>P. yoelii</i> infection with sporozoites and that bioluminescent imaging can be used to monitor protective efficacy of attenuated parasite immunizations. Thus, this rapid, simple and noninvasive method for monitoring <i>P. yoelii</i> infection in the liver provides an efficient system to screen and evaluate the effects of anti-malarial interventions <i>in vivo</i> and in real-time.</p>