Plasmodium

The infection agent causing malaria. Many different species causing malaria in different animals. Can be transmitted by Culicidae flies.

Life Cycle of Plasmodium

Infection begins with the bite of an infected mosquito, usually Culex or Aedes species. Sporozoites introduced with the salivary gland secretions are carried to the reticular cells of the spleen. Each sporozoite develops into thousands of merozoites. These merozoites rupture their host cell and invade endothelial cells or other cells of the reticuloendothelial system to complete another cycle of replication. The merozoites then rupture that host cell and enter erythrocytes in the blood stream. This initiates the intra-erythrocytic cycle. Merozoites multiply in the RBC, forming a schizont (shizogony). The schizont will rupture, killing the RBC and releasing the merozoites to infect more RBCs. During schizogony, the parasites feed on the RBC cytoplasm, ingesting haemoglobin. The intra-erythrocytic cycles continue until the host dies or the parasites are suppressed by host immunity. After the initial cycles in erythrocytes, a few merozoites develop into sexual cells (microgametes and macrogametes) with each new cycle. The sexual cells are maintained in the RBC until they are consumed by a mosquito with its blood meal.

In the mosquito: the sex cells are released and fertilization and zygote formation occur. The zygote matures into an elongated mobile cell that crosses the midgut wall. This cell becomes an oocyst which divides into thousands of spindle-shaped sporozoites. The oocyst then bursts and releases the sporozoites, some of which migrate to the salivary gland where they are injected into a host during the mosquito’s blood meal.

Disease

Malaria - Birds