U.S. Health Departments Warn About Mosquitoes Testing Positive for West Nile Virus

Several local health departments in the U.S. warned residents this week that officials have detected mosquitoes carrying West Nile virus in states across the country. 

In New York, Suffolk County announced Monday that 16 mosquito samples have tested positive for the virus, which can sometimes be life-threatening, bringing the total number of mosquito samples testing positive for the virus so far this season to 32. In New Jersey, Cape May County health officials said Monday that they’ve detected seven positive West Nile virus collections during the months of June and July. Denton County Public Health (DCPH) in Texas also said Monday that five mosquito traps in unincorporated Denton County tested positive for West Nile virus, adding that the areas would be fogged three times over the following days. 

The next day, DCPH reported the first 2024 human case of West Nile virus in the county; that patient was diagnosed with a serious form of the virus, called West Nile Virus Neuroinvasive Disease, which can lead to death or long-term disability.

“We’re seeing more positive mosquito traps in the last few weeks indicating increasing risk for contracting West Nile Virus, just as we’ve seen in our first human case of the summer,” DCPH Assistant Director and Chief Epidemiologist Juan Rodriguez said in a press release on Tuesday. “We ask community members to take preventive actions to lower their risk of contracting a mosquito-borne illness.”

All three local health departments advised residents to take steps to protect themselves, such as minimizing time outdoors between dusk and dawn, using mosquito repellent, draining standing water on your property to reduce mosquito breeding sites, and wearing long-sleeved shirts or long pants when mosquitoes are active.

“The confirmation of West Nile virus in mosquito samples indicates the presence of West Nile virus in the area,” Suffolk County Health Commissioner Gregson Pigott said in a press release. “While there is no cause for alarm, we advise residents to cooperate with us in our efforts to reduce exposure to West Nile virus and other mosquito-borne diseases.”

Read More: The Scents and Colors Mosquitoes Are Drawn to

West Nile virus is the most common mosquito-borne disease in the U.S., according to the U.S. Department of Health and Human Services (HHS). If a mosquito carrying the virus bites a human, that person can become infected with the virus. 

About 80% of people infected with West Nile virus won’t have any symptoms, but about 20% may develop a fever and other flu-like symptoms, according to the HHS. Less than 1% of people develop severe West Nile Virus Neuroinvasive Disease, according to the HHS. So far this year, 24 cases of West Nile virus have resulted in neuroinvasive disease in the U.S., according to the Centers for Disease Control and Prevention (CDC).

So far this year, 45 human cases of West Nile virus have been reported in 19 states, according to data from the CDC. This is lower than the 422 cases that were reported from January to July of 2023, according to CDC data. Cases of West Nile virus usually start to increase in July, peak in August, and remain high in September, CDC data shows. States with the most reported cases so far this year include Texas at 9, Nevada at 8, and Nebraska at 7, according to the CDC.

Last month, the Southern Nevada Health District said that 91 mosquito pools, comprising more than 3,000 mosquitoes, tested positive for West Nile virus.