Image: Wikipedia - Heironymous Rowe Mosquitoes and other blood-feeding insects are attracted by exhaled carbon dioxide and volatile organic compounds produced by their hosts. Scientists at the University of California, Davis have now identified a compound produced by both humans and birds that acts as an attractant for the Culex mosquitoes which transmit West Nile virus. Birds are the principal hosts for West Nile virus and act as amplifying hosts from which the virus can be transmitted to humans and other mammals by mosquito bites.
The discovery of a common semiochemical produced by birds and humans may explain the observed shifts in Culex feeding from birds to humans and consequent transmission of West Nile virus to human populations. Four compounds were found to dominate odorant profiles of humans from different ethnic backgrounds and one of these – nonanal – was also the predominant compound in profiles of both chicken and pigeon. Olfactory receptor neurones in the antennae of Culex quinquefasciatus (Southern house mosquitoes) were shown to be exquisitely sensitive to nonanal, and field populations were attracted to traps baited with the odorant. When nonanal and carbon dioxide were combined, more insects were trapped than when using either bait alone. West Nile virus is now the dominant vector-borne disease in North America and the presence of a common semiochemical in birds and humans may explain the shift in feeding behaviour of Culex mosquitoes that occur in late summer when migrating birds disperse.
The study is published in the journal PNAS.
An earlier study found significantly higher amounts of nonanal in older subjects, raising the question of whether Southern house mosquitoes show a preference for older folks.