Plasmodium vivax - This is the most common species of human malaria. All species of Plasmodium are transmitted by mosquitos Other human species include P. malarie, P. ovale, andP. falciparum. In addition to those occurring in humans, Plasmodium species occur in many other mammals and avians.
The life cycle involves sporozoites being introduced with the bite of the infected mosquito. Sporozoites enter hepatic-like cells and go through cryptic-schizogony. Merozoites enter either new hepatic cells or RBCs. A-sexual multiplication occurs in RBCs resulting in either the occurance of additional intraerythrocytic trophozoites (above left) or gametocytes. If gametes are picked up along with the blood meal taken by a susceptible mosquito, these gametocytes initiate the sexual cycle. The zygote (Ookinete) (center) penetrates the stomach wall of the mosquito and encysts (oocyst) (right) on the outside wall. A-sexual division results in sporozoites that migrate to the salivary glands and are capable of producing an infection when inoculated by the feeding mosquito.
Haemoproteus columbae - This is one of the malaria like-parasite of birds. Only gametocytes (above) appear in peripheral RBCs. Schizogony occurs in endothelial cells of blood vessels. Hippobosid flies are the typical vector for most species. Most cases are asymptomatic with a large percentage of wild birds, especially morning doves, being infected. Concurrent infections with Leucocytozoon spp are common.
Leucocytozoon spp- This is another malaria-like organism infecting birds. Gametocytes (above) occur in greatly distended RBCs while schizogomy occurs in liver cells. There are several important species in birds with some being pathogenic, especially in young birds. Various species of this genus are a common parasite of hawks, owls, and waterfowl. Transmission involves blackflies as vectors.