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An increase in West Nile virus cases in Georgia – from two in August to seven last week – has spurred concern, as county health departments take steps to control mosquitoes, which spread the disease.
Nationwide, 377 cases have been reported this year, according to data from the U.S. Centers for Disease Control and Prevention.
“There’s clearly high risk circulating in the environment among the mosquitoes here … When there’s a cluster of cases, the likelihood for additional cases is higher than an average year,” said Emory University infectious disease expert Dr. Matthew Collins, who considers the disease a “moderate concern” in metro Atlanta.
Collins urged people to take precautions against mosquito bites, but said there’s no reason to panic.
“Driving in Atlanta is probably much higher risk than getting West Nile in Atlanta,” Collins said.
Two human cases of the virus have been identified in Fulton County, with one each in DeKalb, Cherokee, Hall, Richmond, and Chatham counties as of Sept. 3, according to the CDC.
Of the seven, four cases have been the more serious “neuroinvasive” type, which can affect a patient’s brain or spinal cord and lead to confusion, severe headache or loss of consciousness.
Officials doing West Nile virus surveillance
The Georgia Department of Public Health tracks West Nile virus by identifying birds, horses, and mosquitoes that test positive, which helps determine the areas where people are most at risk, spokesperson Nancy Nydam said.
Local public health departments focus on preventing mosquito breeding, but each county uses a slightly different approach.
In DeKalb County, public officials do not spray for mosquitoes but rather use larvicide. That is environmentally friendly and prevents mosquito larvae from becoming biting adults, spokesperson Eric Nickens said.
In Fulton County, if West Nile virus is detected in mosquitoes, officials will visit all residents within a quarter-mile of the area to urge precautions. Fulton uses insecticide spraying and larvicide to try to control mosquitoes, spokesperson Darryl Carver said.
“In Georgia, mosquito season lasts into October and sometimes into November, depending on weather conditions. As long as mosquitoes are active, and we know [West Nile virus] is circulating, elevated risk exists,” Nydam said.
Virus goes from birds to mosquitoes
West Nile is spread to humans by mosquitoes, typically Culex mosquitoes that become infected when they bite infected birds. The mosquitoes can then transmit the disease to people, horses, and other mammals, according to the CDC.
People are “dead-end hosts,” according to the CDC. An infected human will not pass the disease on to a mosquito if bitten. However, the disease can be transmitted from one human to another through blood transfusion or organ transplantation, as well as from mothers to babies through pregnancy, delivery or breastfeeding.
West Nile virus was first identified in the United States in New York City in 1999. It is named after the West Nile region of Uganda, where it was originally discovered in 1937.
The spread of West Nile is likely affected by climate change, Collins said. But it’s difficult to draw a direct line between increased temperatures and increased incidence of the disease. Rather, there are “multiple factors” that include the location of bird and mosquito populations, temperature and rain.
Severe cases of West Nile virus are rare
Many people infected with West Nile virus feel no or mild symptoms, and those cases are likely to go unreported, Collins said. Other people may have more moderate symptoms like rash, fever, headache, an upset stomach or diarrhea that will last for a few days and then subside.
The “neuroinvasive” forms, which can cause paralysis, are rarer and more likely to develop in elderly people or those with other health conditions, Collins said.
About two-thirds of cases reported so far this year — 255 of 377 — have been neuroinvasive, according to CDC data. Four of Georgia’s cases have been neuroinvasive.
Testing for the disease is “not great,” Collins said. A simple blood draw can show evidence of past infection but may not indicate infection at the time of the test.
The most definitive diagnosis comes from testing spinal fluid obtained through a lumbar puncture, he said.
Strongest defense: Avoid mosquito bites
There is no commercially available vaccine or treatment for West Nile virus, beyond supportive care, which could include attempting to cool the body in the case of very high fever and breathing support if needed.
Preventing mosquito bites is the strongest line of defense, Collins and the state Department of Public Health emphasized.
Steps people to prevent bites include:
- Limiting exposure at dusk and dawn, when mosquitoes are more likely to bite
- Wearing longer-sleeved clothes and pants to reduce skin exposure
- Using insect repellent with the chemical DEET
- Ensuring that doors, windows and screens are tightly closed so that mosquitoes cannot come indoors
- Emptying containers, including outdoor pools and buckets, that contain standing water where mosquitoes can breed.
Insect repellents with the chemical DEET are safe, Collins said.
Rebecca Grapevine is a reporter covering public health in Atlanta for Healthbeat. Contact Rebecca at rgrapevine@healthbeat.org.
