Avian Malaria

All variants of malaria is caused by infection with parasites in the genus Plasmodium and there are quite a number of these pesky parasites. The genus Plasmodium consists of over 200 species, generally described on the basis of their appearance in blood smears of infected vertebrates. These species have been categorized on the basis of their morphology and host range into 14 subgenera.

In humans, malaria is caused by six Plasmodium species: Plasmodium falciparum (~75%), Plasmodium vivax (~20%), Plasmodium malariae, Plasmodium ovale curtisi, Plasmodium ovale wallikeri, and Plasmodium knowlesi.

But some species of Plasmodium also infect birds and then causes avian malaria. Avian malaria is usually caused by Plasmodium relictum. Yes, there are several other species of Plasmodium that infect birds, such as Plasmodium anasum and Plasmodium gallinaceum, but these are of lesser importance

Avian malaria is found worldwide, with some important exceptions. Usually, it does not kill the infected birds. However, in areas where avian malaria is recently introduced, such as the islands of Hawaiʻi, it can be devastating to birds that have lost evolutionary resistance over time[1].

The parasite seems to be evolving to evade immunity, while it also seems to be able to expand its geographical range[2].

[1] McClure et al: The role of native and introduced birds in transmission of avian malaria in Hawaii in Ecology – 2020
[2] Theodosopoulos et al: A highly invasive malaria parasite has expanded its range to non-migratory birds in North America in Biology Letters – 2021