What is malaria?
In humans, malaria literally means bad air—a term inherited from the days when people believed that foul air blowing off swamps and bogs caused the disease. They were right, but indirectly: it isn’t air itself, but the infected mosquitoes that fly with it that pass on the disease—a parasitic disease caused by organisms that live and multiply in blood.
Birds are bitten by mosquitoes too, so it’s no surprise that birds get malaria. Malaria in birds can be very similar to human malaria, but avian malaria is not caused by exactly the same parasites as human malaria is.
Confusion arises over what is actually malaria in birds. Human malaria is caused by four species in the genus Plasmodium—malaria and plasmodium are used synonymously to refer to the parasite and, for many people, malaria is only caused by Plasmodium spp. Malaria, however, is the name of the disease, not the parasite. In birds, parasites belonging to at least three related genera multiply in red blood cells: Plasmodium, Haemoproteus, and Leucocytozoon. In birds, therefore, the word malaria may refer to an infection with any of these parasites.
This article deals primarily with the malaria of birds caused by Plasmodium spp.
A short history of malaria and birds
In 1885, a few years after human malarial parasites were first observed in red blood cells, a physician in Russia found the parasites in the blood of birds. The life cycle of plasmodium was not yet known, and for a time researchers wondered if malaria might be passed from birds to humans. It was a fruitless line of investigation; however, birds did help solve the mystery of how humans get malaria—Robert Ross was researching malaria using birds as a model in 1898 when he proved that mosquitoes spread the parasite.
By 1938, three genera of blood parasites were recognized in birds: Plasmodium, Haemoproteus, and Leucocytozoon. Plasmodium and Leucocytozoon both cause serious disease in some birds, while Haemoproteus causes few or no symptoms of illness. Research on the malarial parasites of birds has not been as intense, however, as the study of Plasmodium spp. and malaria in humans.
What birds catch malaria?
Many different birds harbour Plasmodium spp. Ducks, penguins, falcons, pigeons, and canaries all suffer from malaria, and the disease causes high mortality in domestic poultry flocks. In passerine birds, however—songbirds or perching birds—the parasite remains in the circulating blood and infects biting mosquitoes but causes no disease. This means that songbirds are an important reservoir of avian Plasmodium spp. in nature, a source of infection for more susceptible birds.
Symptoms of malaria in birds
A bird that has symptoms from Plasmodium spp. infection generally has many parasites multiplying in the circulating blood within a week of the mosquito’s bite. Birds suffer loss of appetite, fever, weakness, depression, and shortness of breath. Blood circulation to organs may be impaired, and the liver and spleen may be enlarged, with anemia due to destruction of red blood cells. In heavy infections death is common.
Can bird malaria be treated?
Birds can be given antimalarial drugs, usually the same as those used for humans. This is only practical, however, in domestic poultry flocks, birds living in zoos, or pet birds. For wild birds, there’s little that can be done.
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Sources:
Desowitz, Robert S. The Malaria Capers. New York: W. W. Norton and Company, 1991.
Jennings, Leisa, Julie Webb, and Bruce E. LeRoy. "Avian Malaria." The University of Georgia College of Veterinary Medicine.
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