Officials Issue Alerts About Potentially Deadly Mosquito-Borne Virus Across US

A micrograph of the West Nile Virus in a 2014 photo. Cynthia Goldsmith, P.E. Rollin, US Centers for Disease Control and Prevention

Health officials say that they are discovering mosquitoes with West Nile virus, a potentially fatal illness, across multiple states in recent days.

On Thursday, authorities in Des Moines, Iowa, announced that virus-positive mosquitoes were found in surveillance traps and through testing them. The city said that it is now performing city-wide testing.

“Treatments will continue over several nights to cover the entire community, and applications in residential areas will generally begin after 8 p.m.,” the City of Des Moines said in a news release. “The treatment will help reduce the local adult mosquito populations that may transmit the virus to people and pets, helping preserve Des Moines residents’ health and comfort.”

The Metro Nashville Health Department in Tennessee, too, said this week that mosquitoes in southeastern Nashville tested positive for West Nile virus after capturing the insects at a trap near an intersection. And in Nebraska, officials in Lincoln reported Thursday that mosquitoes tested positive for West Nile virus, potentially indicating community transmission.

Around the same time, officials in San Antonio, Texas, also said that West Nile virus was detected in a pool of mosquitoes. The virus was also found in the Dallas area in Arlington, Coppell, Lancaster, and Seagoville, authorities said, while the Dallas County Health and Human Services said Tuesday it will start spraying for mosquitoes.

West Nile-positive mosquitoes were also located in Austin, the capital, and Georgetown, Texas, this week, according to officials.

None of the health agencies have reported any human cases of West Nile virus so far this week. Seventeen cases have been reported across the United States so far, according to the U.S. Centers for Disease Control and Prevention (CDC), including Oregon, Arizona, Wyoming, South Dakota, Nebraska, Iowa, Missouri, Louisiana, South Carolina, and Georgia.

Mosquitoes in a container in a laboratory in Germany, which saw its first case of West Nile virus in 2019, in a 2019 file photograph. Steffen Kugler/Getty Images

Data from the CDC show that West Nile virus in humans is relatively rare in the United States. About 1,100 cases of the virus were reported in all of 2022 across all 50 states, while about 2,900 cases were reported in 2021. Over the past 20 years, 2003 saw the highest number with about 10,000 confirmed cases.

But the agency said that the “annual number of reported WNV (West Nile virus) disease cases can fluctuate widely, as a result of periodic epidemics,” according to its website. “All residents of and visitors to areas where WNV activity has been identified are at risk of WNV infection, particularly people who engage in outdoor work and recreational activities.”

In California, meanwhile, there have been around 7,500 human cases and more than 300 deaths reported since 2003. However, no human cases have been reported so far in the Golden State for 2023, state data show.

“Cases of West Nile virus have been reported in states across the continental United States,” said the CDC, adding that virus “activity typically occurs during the summer months and into the fall.”

While the health agency has issued an alert recently about mosquito-borne malaria cases, West Nile virus is actually the top cause of mosquito-related disease in the United States, it says. Like malaria, West Nile virus is spread via the bite of an infected mosquito.

“There are no vaccines to prevent or medications to treat WNV in people,” the health agency says. “Fortunately, most people infected with WNV do not feel sick.”

However, officials say that about 1 in 5 people, or 20 percent, develop a fever and other symptoms, while 1 out of 150 infected individuals develop a severe and sometimes fatal illness. Some symptoms other than fever include a headache, body aches, joint pains, vomiting, diarrhea, or rash.

Most people with a febrile illness caused by West Nile virus recover completely, the CDC says, but fatigue and weakness can last for weeks or months.

Health officials have advised residents to protect themselves from mosquito bites by using repellent, wearing long sleeves, and wearing long pants. They also called on people to drain pools and puddles with standing water, which is where mosquitos lay their eggs. People were advised to also keep their gutters clear of debris, cover their trash containers, and change the water in pet dishes.

Authorities have also noted that some bug repellents are not suitable for children, adding that people should avoid applying them to the hands of kids. Parents also should avoid using DEET for children.

As for malaria, four cases were detected due to local transmission via mosquitoes in Florida. Another case was found in Texas this week, the CDC said.

The agency said that there is “concern for a potential rise in imported malaria cases associated with increased international travel” in the summer of 2023, adding that there is also a “need to plan for rapid access to” intravenous artesunate, a medication that derives from the sweet wormwood plant Artemisia annua. The CDC classifies the drug as “the first-line treatment” for severe cases of malaria in the United States.