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Avian malaria in Western Cape birds
Avian malaria occurs worldwide on most continents. In the Western Cape it affects canaries and weavers especially. It is nevertheless reassuring to note that a person cannot catch the same form of malaria that occurs in a bird.
By Sharon Okanga
Avian malaria is a blood infection of birds that remains obscure, despite an increasing amount of research into the disease. It occurs worldwide on most continents, in both temperate and tropical regions. Whereas people only get infected by the Plasmodium strain of haemosporidia, there are three separate known strains that cause infection in birds: – Plasmodium, Haemoproteus and Leucocytozoon. The Plasmodium species and the vector (or mosquito) species carrying the infection differ between birds and humans, so it is reassuring to note that a person cannot catch the same form of malaria that occurs in a bird However, the malaria story in birds is no less dire than it is for the human form of the disease. When it was introduced in Hawaii, avian malaria caused the extinction of more than 70% of the native population of the Hawaiian honeycreeper. Rising temperatures resulted in an expansion of the mosquito vector’s range – as a result, there has also been a marked retraction in the natural range of the Hawaiian honeycreeper.
African wild birds have had more exposure to the disease and can act as natural carriers for the disease without succumbing to it. Despite this, avian malaria has proven fatal in chickens, and fatalities have also been reported in ostriches and penguins – birds that hold high socio-economic and conservation status respectively in South Africa. Although avian malaria occurs in South Africa, little is known about its ecology, or even where it tends to occur.
Over the past two years, fieldwork was carried out investigating the prevalence and incidence of avian malaria in Western Cape passerines - the work was the main rationale of a PhD project based at the Percy FitzPatrick Institute of African Ornithology, UCT. Part of our research interest was to find out which bird species seemed most susceptible to infection and whether malarial haemosporidia showed a preference towards particular species. Blood samples were taken from approximately 1000 birds sampled from 26 wetland sites situated around the Western Cape.
Because malaria is a seasonal infection that tends to be influenced by factors such as rainfall and temperature, site visits were conducted twice, with each site visited once in summer and winter. From the bird species caught, current results indicate that avian malaria tends to predominate more in some bird species compared to others: for example the canaries and weavers showed markedly higher infection prevalence than other bird families. Results also showed that different strains of the haemosporidia are more prevalent in particular bird families. There is also some indication that site location plays a role in the incidence of disease.