Water Quality, Urbanization, and West Nile Virus

Graeme Lockaby and Latif Kalin, Clinton-McClure Professor and associate professor, respectively, at the School of Forestry and Wildlife Sciences, have been awarded a $240,000 grant from the U.S. department of Agriculture Urban and Community Forestry Program to fund research that will study the links between urbanization and West Nile Virus.

The project, “Impact of Forest to Urban Conversion on Human Health,” will be conducted in collaboration with Wayne Zipperer at the U.S. Forest Service Southern Research Station, the Department of Epidemiology at the University of Alabama at Birmingham, the Center for Disease Control in Atlanta, Ga., and the Georgia Department of Community Health, as well as SFWS faculty members Krisztian Magori and Wayde Morse, and doctoral student Navideh Noori.

Lockaby, who is also director of the Center for Forest Sustainability, has previously worked extensively with the impact of urbanization on water quality. It was this work that sparked his interest in urban stream quality and human health, and exploring what role research from the School of Forestry and Wildlife Sciences might play in exploring these issues. Lockaby’s previous experience with sampling water in rural areas did not prepare him for what his graduate research assistant Jackie Crim found when sampling streams in Columbus, Ga.

“After Katrina, they were talking about the high levels of fecal coliform in the streets of New Orleans, but the data Jackie was collecting were three times that level after a storm. No disaster – just routine rainfall patterns,” he says.

The magnitude of the problem became more evident the more he looked. The streams are in neighborhoods, with no way to assess who had exposure to streams at what times, and how that might relate to illnesses. He explains one of the problems: “A child goes in a stream – children will play in water – and gets sick two days later. Is it because of bad water or some bad milk?” There was just no clear way to study the epidemiology of it.

However, with West Nile Virus, there is a clear test – a person either has it or does not. Past studies have shown a direct link between poor water quality and increased mosquito populations, including the species that is responsible for the spread of West Nile Virus. This seemed like one way to attack the problem. However, precise data linking land-use change and West Nile Virus risk is lacking.

“Many of the environmental factors associated with West Nile Virus remain unclear,” says Lockaby. “What we, as a natural resources unit, bring to the table is the ability to do a very detailed analysis of the landscape, including aspects that may contribute to risk.”

Krisztian Magori, a quantitative disease ecologist, has joined the School of Forestry and Wildlife Sciences as a postdoctoral fellow for this project. Previous research, said Magori, gives conflicting evidence on what conditions present the most risk for mosquito-borne diseases such as West Nile Virus.

“In my viewpoint, the whole project is about the effects of urbanization and deforestation on human health,” says Magori. “Dr. Lockaby and others have done a great job showing that urbanization and deforestation definitely have effects on streams. Now we are trying to bring together data sets of water quality and hydrology, land-use/land-cover changes, and occurrences of West Nile Virus to see if there is really a link between urbanization and mosquitoborne diseases, how we can best describe that linkage, and what we can do about it.”

The project will begin with a mesocosm-scale study and move on to a broad landscape-scale study involving real stream sources and West Nile Virus outbreaks. “This is about predicting risk,” said Lockaby. “We don’t want to just say bad water quality probably means more mosquitoes. We want to show a numerical relationship to help prevent infection.” West Nile Virus was responsible for hundreds of reported infections and many deaths in the United States in 2012, but Magori thinks the impact of the disease could still be underestimated. A recent study suggested that up to 3 million people nationwide could have been infected since the disease hit U.S. shores in 1999. He adds that a Texas study suggested that a small percentage of those infected – including people who never showed symptoms – can experience long-term health problems.

Even considering only the worst cases of West Nile Virus and the potential for ongoing problems, the economic costs for treatment are high despite the low incidence of the disease in most years. However, they hope the Auburn study will have even broader implications. West Nile Virus, Lockaby points out, is one of a wide array of mosquito-vectored diseases like dengue fever, which can be devastating and has begun to make an appearance in the United States recently. He hopes the methodology they develop can be applied to a variety of these diseases, which may begin to be more prevalent in the United States as we see increasing climate variability, as well as assessing other health impacts of polluted water.

Since receiving the grant, the team has completed one pilot study and are beginning a second more replicated mesocosm-scale study to assess ideal breeding conditions for mosquitoes that commonly bear the West Nile Virus. The mesocosm study is essentially a container-based experiment using containers with varying levels of chemical contaminants commonly found in stream water.

The water came from a forested stream, and they first added leaf litter to breed bacteria that mosquito larvae eat. Some containers received only water, some only additional leaf litter, and others received nitrate, phosphate, ammonia, or a combination of ammonia and phosphate. Then they added 300 mosquito eggs to each container, obtained from Professor Nannan Liu of the Entomology Department.

Although the eggs hatched more slowly than the usual time frame due to the advent of cooler weather, the information from the pilot study enabled the development of the much larger second study with six identical replications of 19 concentrations of nitrogen and phosphorous concentrations. This study will provide insight into the most ideal breeding conditions for these mosquitoes, which are generally believed to require water with some degree of pollution. There has previously been no study of this in the scientific literature.

As their mosquitoes ripen, Noori and Magori check each container daily and take photos. Any larvae that show signs of moving to the next stage of growth (pupae) are removed into individual vials. Each adult female can produce 100 eggs, Magori says.

Meanwhile, a selection process is under way for potential field sites spanning a range of environmental conditions in the Atlanta metro area, where numerous cases of WNV-infected mosquitoes have been documented. Field crews will collect socio-economic and vegetation data for these sites, and the team will work to relate those data to WNVinfection data.

Although foresters and professionals across the natural resources career field know that forests and green spaces are important, this study has the potential to bring into focus an additional, much more specific benefit of forestland – human health. As they study the connection between pollution in urban water sources and outbreaks of mosquito-borne diseases like West Nile Virus, Lockaby, Magori, and Noori are forging a new collaboration between fields of public health and natural resources.

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