Just like people, birds have the misfortune of being visited by a variety of blood-sucking insects, insects that can transmit all manner of parasites through their bites. Some of those parasites, including ones related to human malaria, come in the form of haemosporidia--single-celled protozoans that take up residence in their host's bloodstream. Using modern lab techniques, scientists are now able to discover the diversity of these parasites living in the bloodstream of wild birds by isolating their DNA from the blood of infected birds. Holly Lutz, a PhD candidate at Cornell University and graduate research fellow at the Field Museum, led a collaborative team of scientists from Cornell, the Field Museum, and the University of North Dakota to address questions about patterns in the diversity of these parasites in a study published today in the journal PLOS ONE.
The work for this project began in 2009 on a Field Museum expedition to Malawi--on that trip, we came back with hundreds of blood samples from over 150 species of birds, all saved on paper that is specially treated to preserve DNA. Holly, who at that time was a research assistant on the Field Museum’s Emerging Pathogens Project, returned to the lab from Malawi and started working with those blood samples, testing them for three types of avian blood parasites: the malaria parasite Plasmodium and its close relatives Haemoproteus and Leucocytozoon.
What she found was an extraordinarily high rate of infection (nearly 80% of birds!), higher than had ever been previously reported in wild birds, including many lineages of parasites that probably represent undescribed species. She and her co-authors (including me) also tried to understand what ecological variables might be driving the rates at which different birds are infected by these parasites. Among other discoveries, they found that birds that build closed cup nests, like weavers and cisticolas, have higher rates of Plasmodium infection (which is transmitted by mosquitoes) but lower rates of Haemoproteus infection (which is transmitted by biting midges) than other birds. This may be because mosquitoes find their host by detecting airborne chemicals called kairomones that those animals release as they breathe, whereas midges might rely on visual cues (like actually seeing the bird). The enclosed space of a closed cup nest can lead to the concentration of kairomones, making it easier for mosquitoes to locate, while at the same time obscuring the bird from view, thus making it more difficult for biting midges to find.
There is still a lot to learn about these parasites, which are poorly studied in most tropical regions of the world. For example, are the patterns of infection that we found in birds of Malawi similar in other bird communities? What are the effects of malaria parasites on their hosts, and to what extent do different species of birds share different species of parasites? Holly and her colleagues will continue to explore these questions, relying on the Field Museum's extensive collections of blood samples from Africa and South America.
Lutz, H.L., W.M Hochachka, J.I. Engel, J.A. Bell, V.V. Tkach, J.M. Bates, S.J. Hackett, and J.D. Weckstein. 2015. Parasite prevalence corresponds to host life history in a diverse assemblage of Afrotropical birds and haemosporidian parasites. PLoS ONE.