Salivary gland sporozoite in vivo infectivity was checked by i.v injecting in C57BL/6 mice. Initially, 5,000 sporozoites from WT GFP or Pla1- were used, and while the appearance of blood-stage infection was observed on the third day in all mice infected with WT GFP, a delay of 2.5 3.5 days was observed in the appearance of Pla1- blood-stage infection.To quantify the sporozoite invasion and subsequent development in the liver, we infected mice with 5x103 sporozoites and the liver parasite burden was quantified at 40 h p.i. by measuring the parasite 18S rRNA copy number using real-time PCR. There was no significant difference in liver parasite burdens between WT GFP and Pla1-. EEFs were also counted at 40 h p.i. in multiple experiments and no difference from wild type was observed, signifying normal productive invasion and development by Pla1- sporozoites (Fig. 4C). EEF growth was also monitored by measuring their areas at 40 h and 65 h p.i., with no significant difference from WT GFP. Subsequently, maturation of EEFs and the formation of merozoites was observed by anti-MSP1 staining. Both nuclear division and merozoite formation appeared normal in Pla1-EEFs. In vitro cell detachment was quantified for Pla1- and comparatively fewer detached cells (DCs) were detected floating in the cell culture medium even up to 70 h p.i. Evidence is presented that Pla1 has a role in merosome release.