Upon inoculation by an Anopheles mosquito into the human dermis, elongated motile sporozoites are injected into the skin or directly into the bloodstream. Sporozoites migrate to the liver and infect a small number of hepatocytes. A single sporozoite gives rise to tens of thousands of asexual parasites called merozoites. After approximately one week, merozoites exit the liver into the bloodstream, leaving no residual parasites in the liver. Merozoites entering the bloodstream begin a cycle of erythrocyte invasion, replication, erythrocyte rupture, and merozoite release that repeats approximately every 48 hours. Symptoms of malaria only occur during the blood stage of infection. A small percentage of blood-stage asexual parasites convert to sexual forms, or gametocytes, which can re-infect mosquitoes. Image modified from ref. 5.