Numbers of nfu liver stage parasites in cultured hepatocytes were similar to those of WT parasites. Quantification of nfu- merosomes, merozoite-filled vesicles budding from mature liver stage parasites, showed a reduction 60% as compared to WT parasites.Prepatency was tested by either intravenous injection of 100 or 10,000 sporozoites or by exposure to bites of 57 infected Anopheles stephensi mosquitoes. Irrespective of the mode of sporozoite delivery, initiation of blood infection was comparable between nfu and WT-infected animals.