Tulare County records first human case of West Nile Virus

Tulare County Health and Human Services Agency discovers first human case of West Nile Virus in the county, advises caution against virus-carrying mosquitoes

Fictional Blood samples with infected west-nile virus, with stethoscope, mask and syringe and other stuff.
Darren Fraser
Published July 21, 2023  • 
1:00 pm

TULARE COUNTY – The first human case of West Nile Virus has been identified in Fresno County’s neighboring region Tulare County, and with positive cases being found in mosquitos, more cases are likely to follow.

As of current reports, Fresno County has not recorded any West Nile Virus (WNV) or St. Louis Encephalitis Virus (SLEV) cases this year. However, the Tulare County Health and Human Services Agency confirmed its first human case on July 19. The agency is asking the public to take preventative measures against mosquitos, which have been found with various positive cases of WNV and SLEV in both counties.

“Due to this increased activity and this reported case, we strongly encourage residents to use safeguards to reduce their risk of contracting both West Nile virus and SLEV through mosquito bites,” Dr. Thomas Overton, Tulare County Deputy Public Health Officer, said in the press release.

According to Laura Flores, acting public information officer for Tulare County, a medical provider submitted the report. The report was then transmitted to Tulare County Public Health via the California Reportable Disease Information Exchange or CalREDIE. Because both WNV and SLEV have been found in mosquitoes in multiple locations this year, Flores expects to see an increase in human infections.

“We do expect that more human cases will occur, but hope that people will take precautions to prevent mosquito bites,” Flores said in an email.

According to the Centers for Disease Control and Prevention, there is no vaccine for WNV or SLEV. Most  people infected with WNV show no symptoms. One in five people infected will develop a fever within two weeks of being bit. Severe cases of the virus – roughly one in 150 – can develop into meningitis or, with SLEV, encephalitis. 

Flores said people over 60 and people with certain medical conditions such as cancer or diabetes, or who are immunosuppressed, are at greater risk for developing serious symptoms.

Delta Mosquito and Vector Control District maintains data on WNV, SLEV and Western Equine Encephalitis Virus (WEEV) for northern Tulare County. According to the District’s latest weekly update, there were 176 positive mosquito samples for WNV; seven positive samples for SLEV; and zero for WEEV. Positive samples were collected from Cutler, Dinuba, Exeter, Farmersville, Ivanhoe, Orosi, Peral and Visalia.

While Fresno County has not recorded any WNV or SLEV cases thus far, Katherine Ramirez – Science Education Coordinator for the Consolidated Mosquito Abatement District – said the county has collected positive mosquito samples for both WNV and SLEV. With respect to SLEV, last year, the first positive sample was not detected until August 31.

In a July 19 press release from Fresno County Department of Public Health, Dr. Rais Vohra, interim public health officer, attributed the rise of positive mosquito samples in the county to excessive moisture as a result of winter storms. 

“This confirmation is a strong reminder that everyone should take this disease seriously and take every precaution to protect themselves and their families from mosquito bites,” Vohra said in the release. He added that disease due to WNF typically increases this time of year, with the highest incidences occurring in summer and early fall.

Health department officials from both counties recommend that the public follow three steps – the Three Ds – to prevent infection. Step one is to deter bites by applying a recommended insect repellent. Mosquitoes are most active during dawn and dusk; therefore, individuals should wear protective clothing when they are out during these hours. Citizens should also replace door and window screens that have holes or that do not properly close. 

Lastly, the public must be aware of the hazards of standing water. Mosquitoes lay eggs and develop in this environment. County officials recommend draining all standing water. The public is encouraged to notify public health officials of swimming pools that have either been abandoned or are not being properly maintained.

Darren Fraser