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First Human West Nile Virus Infection of 2023 Reported

Alameda County Public Health Department and the Alameda County Mosquito Abatement District (ACMAD) confirmed the first human case of West Nile virus (WNV) for the 2023 season at the end of last week. The first positive mosquito pool was reported in January 2023.

Alameda Post - a mosquito, one of the vectors for West Nile virus, on skin

The affected individual is a resident of the city of Alameda. According to Regulatory and Public Affairs Director Erika Castillo, the individual was known to have traveled before the diagnosis, so ACMAD is working to determine if the infection took place locally or elsewhere. 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.

When contacted by the Post about Alameda’s policy regarding mosquito abatement, Public Information Officer Sarah Henry stated, “The City has been in contact with the Mosquito Abatement District and shared information with the public about how they can protect themselves,” including ways to protect against the virus and report birds. Henry further stated that Alameda County has been setting traps to reduce the mosquito population and confirmed that the Recreation and Parks Department does not spray Alameda parks against mosquitoes.

To date, ACMAD has found a total of five 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 yet this year, it 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 from a mosquito bite. Mosquitoes can get West Nile virus when they bite an infected bird. In turn, the mosquito can then pass the virus to humans. The best thing people can do to protect themselves from West Nile virus is to avoid mosquitoes and report any dead birds.

How to avoid mosquitoes

There are many ways to avoid mosquitoes and reduce their population:

  • 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 any torn screens.
  • Report dead birds to the West Nile virus call center: 1-877-968-2473 or online.

At this time, 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 one percent 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.

All residents of the city and county of Alameda should keep in mind the importance of taking personal and community protective measures to safeguard themselves and their neighbors against West Nile virus. For more information about West Nile virus visit the Alameda County Mosquito Abatement District website.

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