Mosquitoes carrying the West Nile virus have infected more people in the United States this summer than ever before experts say, despite a scorching season that caused severe droughts throughout the country.
According to the Michigan Department of Community Health, there were 105 reported cases of West Nile in Michigan as of Wednesday. Nationally, the Centers for Disease Control and Prevention has now reported 1,993 cases and 87 deaths as of Sept. 4, making it the worst year the country has experienced since 2003.
U. Michigan Public Health Prof. Mark Wilson said though the virus has now been found in almost every county in the United States since it arrived in 1999, it is fairly new to the country. West Nile likely first entered the United States by boat from Israel and spread from bird populations to mosquitoes, before humans began contracting the disease.
Wilson said that while most mosquitoes usually die off during dry conditions, the Culex mosquito, a prominent carrier of the virus, is able to survive with limited rainfall.
“Different species of mosquitoes end up preferring breeding sites and concentrated water that is more often found during the dry season,” Wilson said. “So your backyard might be a suitable breeding place for some species of infected mosquitoes, but a hundred meters down the road where there are houses without much vegetation it might not be.”
Wilson and other experts said they aren’t able to offer a conclusive answer for why there have been so many West Nile cases this year.
JoLynn Montgomery, an assistant research scientist of epidemiology at the UM School of Public Health, said the mosquitoes carrying the virus may have benefitted from irregular seasonal conditions earlier this year.
“It’s likely that we had a pretty mild winter here in Michigan and more of the mosquitoes that were carrying the virus were able to survive over winter,” Montgomery said.
There is no vaccine or substantive treatment for those infected with the virus, Montgomery said. However, she said alternative care methods aimed at restoring hydration can help relieve many symptoms.
Wilson said only a small percentage of infected people — about 20 percent of reported cases — have severe reactions to the virus, and the remaining people that are diagnosed experience “mild flu-like symptoms.”
Sandro Cinti, an associate professor at the UM Medical School, said the extent of how dangerous West Nile is may be exaggerated, noting that those who have serious reactions are often already coping with weakened immune systems.
“You see people in the hospital and they are really sick, but they are the susceptible ones,” Wilson said.
He added that the mortality rate for those who suffer from neurological symptoms is 10 to 15 percent, but this number is still small compared to the number of cases in which patients have mild symptoms or the virus goes undetected.
“If you compare influenza deaths (nationally), they are about 35,000 to 40,000 on an average year,” Cinti said. “West Nile at its best … is 200 to 300.”
Cinti said the best way to protect against the disease is to stay inside in the evenings and early mornings and to wear long-sleeved shirts and pants whenever possible.
