The genus Haemoproteus is composed of protozoa that are parasitic in birds, reptiles, and amphibians. They grow and feed in the red blood cells of an organism, and are transmitted through the use of a blood sucking insect vector such as mosquitoes. There are currently over 150 known species.
The host becomes infected when bitten by an insect that has sporozoites in it's salivary glands. The sporozoites enter the hosts blood stream, and invade the endothelial cells of varying tissues. There they multiply through asexual reproduction, and form schizonts. These burst open to release merozoites into the hosts blood stream, which penetrate red blood cells and mature into either male or female gametocytes. These are then ingested by another blood sucking insect. They undergo sexual reproduction in the insect's midgut and produce oocysts, which rupture to release sporozoites, which migrate to the salivary glands of the insect. The insect takes another blood meal, and transmits the sporozoites to the next host.
They can cause enlargement of spleen, liver, and kidneys. Some species form large cysts in the skeletal muscles of their host. They can occasionally cause death, but are usually not that virulent.