Spatial and temporal variability in the transmission of vector-borne pathogens can be caused by a large array of factors. These include the community composition and dynamics of the host and vector and their interaction with the pathogen. West Nile virus, a multi-host vector-borne pathogen, has infected over a million people in North America in the past 7 years and caused over 22,000 documented human cases of fever and neurologic disease and 820 deaths. Enormous spatial and temporal variability in West Nile virus activity has been evident at local and regional scales. The general hypothesis is that changes in key characteristics of mosquito and bird communities associated with anthropogenic land use cause spatial variation in West Nile virus transmission. Data will be gathered to test this hypothesis through experimental laboratory studies on avian host competence and mosquito vector competence and field research on local scale virus transmission in birds and mosquitoes on an urban-to-rural land-use gradient.
Understanding the mechanistic drivers of virus transmission and the influence of urbanization on zoonotic disease dynamics is critical to improving surveillance and control programs and ultimately reducing the impact of this and other viruses on human and wildlife health. This research will provide a mechanistic understanding and predictive model of the factors that create variability in West Nile virus transmission and will provide a critical framework for the generation of risk maps based on remote-sensing and mosquito surveillance data. A key component of this research is extensive teaching and training of graduate and undergraduate students in ecological veterinary, public health, and medical sciences. The results will be broadly disseminated to the public, policymakers, and other scientists.
The goal of our research was to understand how land use alters the host and vector communities and the environment, and the implications of these impacts on the transmission of an introduced multi-host, multi-vector pathogen, West Nile virus (WNV). We performed a series of field studies and laboratory experiments to develop a mechanistic understanding and predictive model of the factors that influence spatial and temporal variation in WNV transmission across a land use gradient. We found that the conversion of forest into residential and urban areas had a marked impact on mosquito communities, bird communities (which are the most important hosts for this virus), and increased transmission of West Nile virus. Transmission was greatly influenced by the feeding patterns of the mosquito vectors and how these changed with land use. Somewhat surprisingly, there was a single dominant avian host for transmission, the American robin, despite the presence of dozens of other species of hosts available to several species of mosquitoes. Focal transmission in robins suggests the possibility of highly targeted vaccination of this species that could reduce human infection. Our research suggests that predicting the impact of land use on vector borne diseases is in fact possible, but requires a mechanistic understanding of the ecology of the system. In the case of West Nile virus, and many vector borne pathogens, the crucial aspects of the system are: What are the feeding patterns and preferences of mosquitoes – what species of birds, mammals, reptiles and amphibians do they feed on, and how do feeding patterns reflect the relative abundance of these hosts? What is the impact of land use on mosquito and bird communities – how do the abundances of different species change with urbanization? What are the relative susceptibility and infectiousness of birds and mosquitoes to the virus? A key product of this grant was a framework that allows predictions of transmission intensity for a range of vector-borne diseases if these data are available. This grant supported a total of 11 graduate students – 7 PhD and 4 Masters students - and one post-doctoral scholar, and trained 52 undergraduate students of which at least 18 have gone on to graduate studies. Training of these individuals included all aspects of science including field techniques, laboratory methods, molecular diagnostics, statistics and mathematical modeling. Thus, in addition to the science accomplished under this grant, we have trained a new generation of scientists including medical entomologists, wildlife biologists, statisticians, mathematical modelers, and molecular diagnostic technicians.
