Overview
This lecture explains avian malaria, a parasitic disease in birds caused primarily by Plasmodium and Haemoproteus parasites, covering its transmission, effects on bird populations (especially in Hawaii), evolution, and control methods.
Causes and Transmission
- Avian malaria is caused by protozoan parasites of the genera Plasmodium and Haemoproteus.
- It is transmitted by insect vectors such as mosquitoes (especially for Plasmodium) and biting midges (for Hemoproteus).
- Parasites reproduce asexually in birds and both sexually and asexually in insect vectors.
- The disease is found worldwide except Antarctica, with a high diversity of parasite and host species.
Disease Effects and Impact
- Symptoms in birds range from none to severe population declines or death.
- Birds in newly affected regions, such as Hawaiian honeycreepers, are highly susceptible, causing local extinctions.
- Captive and wild penguins are especially sensitive to infection in non-native habitats.
- Loss of red blood cells causes anemia, weakness, and can lead to death in susceptible species.
Evolution, Diversity, and Classification
- Co-speciation and host-switching have led to a complex parasite-host relationship and global spread.
- Classifying parasite species is controversial; molecular methods using cytochrome b gene sequences are now preferred.
- The MalAvi database supports global research into parasite lineage diversity.
Phylogeny and Phylogeography
- Avian malaria phylogeny suggests a distinction between lineages infecting mammals and those infecting birds/reptiles.
- Genetic studies show significant differences between parasite lineages in the New and Old World.
- Vector relationships are under-studied; in Hawaii, Culex mosquitoes are the primary vector.
Historical Research
- Ronald Ross demonstrated mosquitoes' role in malaria transmission, earning a Nobel Prize.
- He used bird malaria to prove mosquitoes transmit the parasite and detailed the infection cycle (sporozoites, merozoites, invasion of organs, RBC destruction).
Epidemiology and Control
- Infection rates are increasing, with climate change expanding the range of vectors and infection prevalence.
- Native birds, particularly in Hawaii, are more vulnerable than introduced species, facing high mortality and extinction risks.
- Control focuses on mosquito management, habitat modification, and supporting resistance in bird populations.
- New approaches like CRISPR gene editing to eliminate mosquitoes are being considered.
Key Terms & Definitions
- Plasmodium — A genus of protozoan parasites causing malaria in birds and other animals.
- Haemoproteus — Another genus of blood parasites affecting birds, transmitted mainly by biting midges.
- Vector — An organism (like a mosquito) that transmits pathogens between hosts.
- Host switching — When a parasite infects a new host species different from its usual one.
- Cytochrome b gene — A genetic marker used to differentiate parasite lineages.
- Anemia — A condition of reduced red blood cells causing weakness and susceptibility to disease.
Action Items / Next Steps
- Review the lifecycle of avian malaria parasites and infection process in birds.
- Read about the impact of avian malaria on Hawaiian bird species and global bird diversity.
- Explore the MalAvi database for lineage information and current research.