FRESNO COUNTY – A human case of West Nile virus in Fresno County led to the death of an individual, the health department announced Wednesday.
The Fresno County Department of Public Health (FCDPH) said in a Nov. 1 press release that the individual who died was one of 10 positive symptomatic human cases of West Nile virus (WNV) recorded in the county this year. Statewide, this marks the 11th WNV death out of 308 total cases in 2023, according to data from the California Department of Public Health (CDPH) updated as of Oct. 26.
“Our heartfelt condolences go to the family and friends,” Dr. Rais Vohra, Fresno County interim health officer, said in the press release. “We need to stay vigilant as mosquitoes continue to test positive for WNV in the county and may continue to cause several severe illnesses, including WNV infection, which can require hospitalization and intensive care.”
Leticia Berber, a health educator with FCDPH, said the individual who died was located in the west side of the county and was a man at high risk of getting sick from WNV.
Those with the greatest risk of developing serious WNV symptoms include people who are over the age of 60, under the age of 5, have received an organ transplant or have a medical condition such as kidney disease, diabetes, high blood pressure, cancer and heart problems.
West Nile virus risks
West Nile virus is a disease spread to humans through mosquito bites. Mosquitos contract the disease when they feed on the blood of birds infected with WNV, the CDPH website says. While WNV is most commonly spread during the hotter months, mosquitoes are present in California year-round and can pose a risk at any point.
Since mosquitoes were first detected in California in 2003, there have been nearly 8,000 total cases of WNV and 384 WNV-related fatalities, according to CDPH data. So far in 2023, WNV-related fatalities are the lowest the state has had since 2019, when there were only six recorded deaths. There were 15 recorded deaths in 2022, 12 in 2021 and 15 in 2020.
According to CDPH, 80% of people infected with WNV do not present with symptoms and up to 20% of people infected with WNV may present with mild symptoms such as fever, nausea, vomiting, headaches, body aches and a skin rash.
Fewer than 1% of people infected with WNV will become very sick, the CDPH website says; however, in those cases the virus can affect the brain and nervous system, possibly leading to encephalitis or meningitis. Severe symptoms include high fever, confusion, vision loss, headaches, neck stiffness, muscle weakness, paralysis, numbness and coma.
CDPH says symptoms usually develop three to 14 days after a bite from an infected mosquito. Mild symptoms will only last for a few days with lingering fatigue and weakness, while severe symptoms can last for several weeks and can permanently impact the brain and nervous system.
Individuals with symptoms can contact their health care provider for testing and evaluation; asymptomatic individuals who test positive for WNV are typically identified through blood tests that occur after blood donations, Berber said.
Protecting yourself from West Nile
Berber said that because WNV has no cure, vaccine or medication, it is vital that individuals protect themselves and their families from mosquito bites.
FCDPH recommends applying insect repellent that contains DEET, picaridin, lemon eucalyptus oil or IR 3535, “especially at dawn and dusk when mosquitoes are most active,” the press release said. Ensure doors and windows have tight-fitting screens without holes or tears and eliminate any standing water around the inside and outside of the home.
Berber said individuals who travel to warmer places, including other countries or different areas within the United States, should also ensure they are still taking protective measures against mosquito bites, even during the winter months.
People should also wear long, loose clothing when going outside and cover any exposed skin to prevent mosquito bites.
When FCDPH identifies human cases of WNV, Berber said the county immediately notifies the community so they are aware of the presence of the disease in their area.
FCDPH has implemented an awareness/advertising campaign about the risks associated with mosquitoes and WNV through radio announcements, billboards and social media posts. Berber said when residents come across a post from the department about WNV or mosquitos, they should click on the links to learn more about the risks and the safety measures they can take.
Katherine Ramirez, science education coordinator for the Consolidated Mosquito Abatement District, which covers just over 1,000 square miles of central and eastern Fresno County, said the most important thing individuals can do to stop the spread of mosquitoes is consistently check for standing water around their homes.
Ramirez recommended that people walk around their homes weekly to check for standing water, especially during the warmer months, and they overturn things like buckets or empty flower pots that could collect water.
“We always want to make sure they (residents) know mosquitoes develop in water,” Ramirez said. “It doesn’t have to be a large source. … Anything that could hold any amount of water, we want to make sure they could dump that out.”
As temperatures decrease, county residents should begin to see fewer mosquitoes, but if there are any in a house, those could continue to reproduce, Ramirez said. Residents and businesses can call their local mosquito abatement district whenever they see mosquitoes and the district will send someone to view the problem and suggest solutions.
Additionally, CDPH says that residents should file a report online if they see a dead bird, especially a crow, jay, magpie, raven, sparrow, finch or hawk.
“Dead bird reports are often the first sign that WNV is active in an area, and the reports help the California Department of Public Health track WNV throughout the year,” the CDPH website says.
Ramirez said that mosquitoes are still appearing at this time of the year because the state saw its first WNV-positive mosquitoes later in the year than what’s usual. She said positive mosquitoes typically show up in late May around Memorial Day, but this year the first positive case didn’t appear until the end of June.
“I think that had to do with our cooler, mild temperatures longer in the spring … and then we just had quite a bit of water everywhere,” Ramirez said.
Even though mosquitoes are still lingering, Ramirez said that as long as someone is not getting mosquito bites, they do not need to worry about contracting WNV; however, mosquitoes can still reproduce in the winter, and precautions should still be taken during the cooler months.
Ramirez said there are not any specific areas within the county that have seen more positive cases of WNV than others and Berber added that the 232 mosquito samples Fresno County has found to be positive for WNV have been from all around the county.
“There isn’t anything that tells us there’s more virus in this location; just because we collect positive mosquitoes doesn’t mean the places we collect negative are fine,” Ramirez said. “Anywhere, you want to make sure you wear insect repellent (and) prevent bites. … There isn’t anywhere that would be safer; we treat every area the same.”
More information on mosquitoes and local abatement/control districts is available at fresnocountymosquito.org.