Since Oklahoma’s first case was confirmed 12 years ago, areas in the state have posted some of the highest rates of West Nile Virus in the nation.
But with predictions of hotter, drier summers due to the effects of climate change, some health officials worry the virus could become even more widespread in Oklahoma and elsewhere.
The virus, spread to humans through mosquito bites, first appeared in Oklahoma in 2002. Since then, there have been 585 confirmed cases of West Nile in the state, including 43 deaths.
As summers grow longer and hotter due to global climate change, those rates may increase, researchers say. The Obama Administration’s National Climate Assessment points to changes in the distribution of pests such as ticks, fleas and mosquitoes as a possible factor in changing rates of the diseases they carry.
The assessment, which represents work done by more than 300 scientists nationwide, was released last month.
According to the assessment, the effects of climate change are already being felt nationwide. The report warns that residents of the Great Plains, including Oklahoma, should expect hotter, drier conditions over the next few decades as those effects intensify.
The report warns of possible increases in the rates of West Nile and other diseases spread by mosquitoes and ticks such as dengue fever, Lyme disease and chikungunya.
U.S. Sen. Jim Inhofe, the most vocal skeptic in Congress of man-made climate change, dismissed the study as “alarmism.” Inhofe, R-Tulsa, called on President Barack Obama to enforce transparency and accountability within the Environmental Protection Agency and criticized the agency for not considering the economic impact of its regulations.
“We can all agree that natural variations in the climate are taking place, but man-made global warming still remains a theory,” Inhofe said. “The president’s climate change policies will only cause a greater disparity in our nation’s income gap and prevent our nation from achieving its full economic potential.”
Prediction is difficult
Oklahoma state epidemiologist Kristy Bradley said the virus seems to multiply more quickly in mosquitoes that carry it when the state experiences hotter, drier summers. The virus also appears to spread more quickly from mosquitoes to humans during hotter conditions, Bradley said.
But Bradley said it’s nearly impossible to predict how severe the virus will be in a single summer, since other factors besides the weather affect the spread of West Nile.
For example, a high rate of infection among birds can lead to a higher rate of infection in humans, since mosquitoes typically carry the virus from infected birds to humans.
The fact that the virus has only been present in the United States since 1999 also means public health officials don’t completely understand how those factors affect the rate of infection, Bradley said.
“We can’t predict from year to year how bad of a season it’s going to be,” Bradley said.
“This is still a pretty new disease to the United States.”
But some doctors say they’re already concerned about the possible health effects of climate change. Dr. Bill Schaffner, an infectious disease specialist at Vanderbilt University, said it’s important for people in Oklahoma and other affected areas to take steps to reduce their risk as West Nile becomes more widespread.
Wearing long pants and long-sleeved shirts and using insect repellant can help minimize exposure to virus-carrying mosquitoes, he said. It’s also important for homeowners to make sure there is no standing water on their property to provide a breeding site for mosquitoes.
“This is close to our heart,” Schaffner said. “It is a smoldering concern for all of us in public health.”