Experts say risk for West Nile infection low as cases mount

As of Friday, 57 cases in Michigan had been attributed to West Nile virus as well as three deaths: One in Washtenaw County, one in Wayne County and one in the city of Detroit. About 88 percent of the cases were neuroinvasive, indicating the severest symptoms of the disease.

The number of cases in Michigan doubled in the span of a week with Friday’s count.

Public health experts maintain that the risk for exhibiting severe symptoms associated with West Nile is low.

About 80 percent of people bitten by an infected mosquito don’t exhibit symptoms.

One out of five people bitten by a mosquito infected with West Nile virus will get sick. Of those that get sick, one out of 150 people may develop serious, neurologic forms of the disease, including meningitis and/or encephalitis.

The mortality rate for those that are severely ill is about 10 to 11 percent.

Meningitis is an infection of the lining of the brain and spinal cord. Encephalitis is an infection of brain tissue. One or both can occur in the most severe cases of West Nile virus.

Milder symptoms of the disease include flu-like symptoms. Signs a person should seek the care of a medical provider include the inability to control a fever, unable to hold liquids down and neurologic signs like muscle weakness, shaking and neck stiffness.

West Nile was first introduced into the U.S. in New York in 1999, when seven people died and 62 people were sickened.

The virus hit Michigan in 2002, when 51 people died and there were 614 cases of the disease, according to data from the Centers for Disease Control and Prevention. It’s been the biggest death toll in Michigan from the virus since that year.

The CDC has been collecting data on West Nile Virus since 1999. However, experts state there’s not enough data to determine trends at this point.

“The problems with any kind of West Nile study … it’s never really stayed in one place long enough to study it,” said Dr. Sandro Cinti, associate professor of infectious diseases at the University of Michigan Medical School.

There are vaccines for West Nile virus for horses, but none for humans. Persons admitted to the hospital for the disease can only receive support treatment.

“The request to the vaccine makers has not been really strong for a vaccine,” said Dr. Eden V. Wells, a clinical associate professor of epidemiology and an associate director of Preventive Medicine Residency at the U-M School of Public Health.

“That’s generally a problem,” Cinti said of the need for a vaccine for certain diseases in general. “There’s either zero demand or full demand.”

A recent survey by AnnArbor.com found most people are somewhat worried about West Nile virus.

Wells called West Nile virus “endemic” at this point.

“I was listening to some federal discussion on this last week,” Wells said. “If the disease is increasing and persists to where there is continued public health impact, there’s more of a call for that. … I think only time will tell about how much of a call there will be.”

Warm weather favorable to the growth and development of the Culex mosquito responsible for transmitting the virus from birds to people has fostered a population experts this season previously said was "suitable for an epidemic" of the virus.

Cinti said the ratio of severe neurological disease to mild disease from the virus is an indicator. This year, about half of the reported cases of West Nile virus nationwide are neuroinvasive.

“The question will be when this settles, are we seeing more severe disease?” Cinti said.

Municipalities in southeastern Michigan don’t fund mosquito control programs. However, the state monitors a number of mosquito pools in some counties. Birds, which are the host species for the virus, also are tracked.

People over the age of 50, or work outdoors in the morning or evening are at a higher risk for West Nile virus.

Wells said the growing number of cases should not be a source of panic, but a sign that it’s important to reduce the chance of exposure to a mosquito bite by taking measures recommended by health officials:

• Make sure window and door screens aren’t broken to keep mosquitoes outside
• Empty containers with standing water
• When outdoors, apply insect repellent that contains DEET or other approved repellent to exposed skin
• Wear long-sleeved shirts and long pants when outside