Severe liver stage attenuation. in Pylinup sporozoite infection with 1,000 sporozoites only one of ten mice became patent and this with delay (day twelve) and seven of twenty mice became patent when infection was done with 10,000 sporozoites with patency in the blood stage positive mice delayed to days seven through twelve. Five of ten mice became patent when using the 50,000 sporozoite dose and patency was delayed to days seven to nine. Highly susceptible BALB/cByJ mice infected with 50,000 wildtype sporozoites all became patent on day three after sporozoite infection, whereas only nine of twenty mice infected with Py linup sporozoites became patent and the day to patency ranged from days eight to ten.Liver stage size measurements revealed that at 24 hours post-infection, Py linup liver stages were comparable in size to wild-type. However, at both 36 and 48 hours post-infection, Py linup liver stages were significantly smaller than wildtype with the size differences being more pronounced at the later time point post-infection. At 48 hours post infection, differences in protein expression and DNA replication/segregation were evident in Py linup liver stages when compared to wildtype liver stages. Specifically, the branching of the mitochondria and apicoplast was reduced and DNA replication as well as DNA segregation appeared significantly reduced. Furthermore, the extensive invaginations of the liver stage plasma membrane that precedes merozoite formation called cytomere formation was severely disordered in Py linup liver stages. This was evident from the changed expression pattern of the parasite plasma membrane marker MSP1, which localizes to the late liver stage schizont plasma membrane.