File:Protozoan parasites and their viral endosymbionts.webp

English: Protozoan parasites and their viral endosymbionts. The life stages in the human (or mammalian) host of Leishmania spp., Giardia duodenalis, Trichomonas vaginalis, Cryptosporidium spp, and Plasmodium spp, are depicted together with a graphical representation of the corresponding viral endosymbionts (see also Table 1). Leishmania. Promastigotes, injected in the mammalian host during a sandfly blood-meal, are taken up by macrophages in the dermis and quickly surrounded by a parasitophorous vacuole (PV). Promastigotes differentiate into non-motile amastigotes and proliferate inside the phagolysosome. Following lysis of infected macrophages, free amastigotes can infect neighbouring macrophages. Infected macrophages and/or free amastigotes may then be ingested by sandflies. Giardia. The cyst ingested by the mammalian host releases trophozoites that multiply by binary fission and colonize the upper part of the small intestine by adhering to the enterocyte surface. Following specific stimuli, trophozoites differentiate back to cysts that are released into the environment in the stool. Trichomonas. Trophozoites are transmitted sexually between humans where, by binary fission, they colonize the lower genital tract of females and the urethra and prostate of males, No cyst form is known. Cryptosporidium. Oocysts ingested by the mammalian host release sporozoites that invade the epithelial cells of the small intestine, form an extra-cytoplasmic yet intra-cellular PV and differentiate into trophozoites. Asexual multiplication by schizogony generates meronts that can infect new enterocytes. Eventually trophozoites differentiate into female macrogamonts and male microgamonts. After fertilization, the zygote develops into an oocyst that will exit the host through the faeces. Plasmodium. Sporozoites injected in the mammalian host during a mosquito blood-meal, invade the hepatocytes, differentiate into trophozoites within a PV and multiply asexually by schizogony giving rise to schizont containing many merozoites (hepatic cycle). Hepatic merozoites then invade erythrocytes (RBC) and the schizogonic multiplication occurs with newly released merozoites capable of infecting new RBC. Trophozoites in RBC can eventually differentiate in male and female gametocytes that will reach mosquitoes during a blood-meal