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August 18, 2023 - First Human Case Of West Nile Virus In Alameda County In 2023

HAYWARD, CA - Alameda County Public Health Department along with Alameda County Mosquito Abatement District (ACMAD) has confirmed the first human case of West Nile Virus (WNV) for the 2023 season. The first positive mosquito pool was reported in January 2023. 

The affected individual is a resident of the city of Alameda. Additional details are not being released to protect the identity of the resident. The district is working with Alameda County Public Health Department to disseminate information about West Nile virus to residents and local healthcare providers.

To date, ACMAD has found a total of 5 WNV-positive mosquito pools within Alameda County. The district traps and tests mosquitoes for the virus throughout the year. While the district has not found West Nile virus positive mosquitoes in the city of Alameda this year, we will continue to trap and test mosquitoes, along with conducting mosquito prevention efforts, such as treating catch basins, removing standing water and educating residents.

Transmission of West Nile virus most commonly occurs through the bite of a mosquito. Mosquitoes can receive West Nile virus from biting an infected bird. In turn, the mosquito can pass the virus to humans. The best thing the public can do to protect themselves from West Nile virus is to avoid mosquitoes and report dead birds. Ways to avoid mosquitoes include:

  • Use a repellant that contains DEET, picaridin, lemon eucalyptus oil or IR3535
  • Wear long-sleeved shirts, long pants, shoes and socks when outside, especially during dawn and dusk when mosquitoes are most active
  • Drain or cover any standing water around your home
  • Irrigate lawns and gardens carefully to prevent water from standing for several days
  • Scrub and change the water in bird baths, fountains, wading pools and potted trays at least once a week, if not more often
  • Make sure window and door screens are “bug tight" and repair or replace torn screens
  • Report dead birds to the West Nile virus call center: 1-877-968-2473 or online at

There is no cure for West Nile virus. The mild form of the disease is commonly referred to as West Nile fever. Symptoms include headache, fever, muscle and joint aches, nausea and fatigue. People typically recover on their own, although symptoms may last for several weeks. The more severe form is often referred to as West Nile neuroinvasive disease. Most people who are infected have no symptoms or only mild flu-like symptoms. Less than 1% of people infected with West Nile virus become severely ill. However, people over 50 and those with weakened immune systems are especially vulnerable to the disease and are more likely to experience serious consequences.

The Alameda County Mosquito Abatement District reminds residents of the importance of taking personal and community protective measures to safeguard against West Nile virus.

For more information about West Nile virus visit Alameda County Mosquito Abatement District (