PARENT SESSION
Contributed Oral Session 94: Toxicology and Disease : Viruses and Epidemics
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 514 A, Level 5, Palais des congrès de Montréal
A Protective Role for Avian Diversity in the United States West Nile Virus Epidemic.
Allan, Brian*,1, Ryberg, Wade1, Langerhans, R. Brian1, Crooks, Kevin2, Ostfeld, Richard3, Chase, Jonathan1, 1 Washington University, St. Louis, MO2 Colorado State University, Fort Collins, CO3 Institute of Ecosystem Studies, Millbrook, NY
ABSTRACT- West Nile Virus (WNV) is a mosquito-borne flavivirus that is carried by birds and transmitted by mosquitoes. Since the introduction of an especially virulent strain to New York City, U.S.A. in 1999, WNV has spread across much of North America, causing over 17,000 reported human cases in the U.S. alone, including more than 650 deaths. WNV is widely believed to occur at higher incidence in urban areas, presumably due to the urban distributions of the most competent vector mosquitoes, which may lead to greater amplification of WNV within bird communities and exposure of humans to the disease. However, it is possible that the reported urban distribution in incidence might be due to urbanization-induced changes in bird communities. Recent ecological theory suggests that variation in host diversity can impact human disease risk–a hypothesis known as the dilution effect–whereby a diverse assemblage of hosts is expected to dilute pathogen transmission by deflecting vector blood meals onto less reservoir-competent hosts. Experimental evidence, while still incomplete, indicates that reservoir-competence for the transmission of WNV to uninfected mosquitoes varies among bird species, with only a few North American species being highly competent. Thus, the dilution effect may be operating in WNV transmission, and we expect to find a negative association between bird diversity and WNV incidence in mosquitoes and humans. In the summer of 2004 we organized a large-scale study in the Saint Louis, Missouri region to determine if the incidence of WNV was more closely related to the abundance of vector mosquitoes or the diversity of bird communities along urban-to-rural gradients. Our results indicated that only low bird diversity was an important predictor of high WNV incidence in vector mosquitoes. Further investigations using county-level data from across the U.S. also supported the dilution effect hypothesis but indicated a negative relationship between human per capita incidence of WNV and human population density, directly contradicting the urban paradigm in WNV research. We suggest that future efforts to control WNV should combine existing vector control programs with efforts to conserve bird diversity, for instance via habitat conservation in urban and agricultural landscapes.
Key words: West Nile Virus, dilution effect