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West Nile Virus
To Report a dead bird or squirrel call 877-WNV-BIRD (877-968-2473) or go to

Number of Positive samples in Alameda County

  2005 2006 2007 2008 2009 2010 2011 2012 2013 2014
Dead Birds 48 30 19 13 10 1 0 15 18


Mosquitoes 9 9 2 1 1 0 0 0 0 15
Squirrels 5 2 1 1 0 0 1 1 0 2
Sentinal Chickens 0 0 0 0 0 0 0 na 0 0
Horses 2 0 0 0 0 0 0 0 0 0
Humans 1 1 0 1 0 1 0 2 0 0

About West Nile Virus

Since 2004, the West Nile Virus has become a fact of life in California.  There are however several stories and rumors surrounding the disease--some of which are either exaggerated or downright untrue.  Because accurate information is critical in times like these, we've assembled this page to give you answers about the West Nile Virus, what we are doing about it, what you can do to help, and a series of other valuable links to other pages dealing with the disease.

If you have any other questions that you think might be important, please email us.


What is West Nile Virus?

West Nile Virus (WNV) is a mosquito-borne disease that has been found in parts of Asia, Eastern Europe, Africa and the Middle East. The virus was first detected in the United States in 1999 in New York City and has since spread through most of the country. Most people and animals who become infected with the virus have only a mild illness or no symptoms, but in rare cases can become seriously ill. The types of mosquitoes that can transmit WNV are common mosquitoes in Alameda County. Our goal is to decrease the numbers of mosquitoes in the county thereby minimizing the possiblity of WNV transmission.

What are the symptoms?

80 percent of people who are actually infected with West Nile Virus will show absolutely no symptoms whatsoever, and the disease often passes unnoticed. 

A little under 20 percent of people will have mild symptoms that develop between 3 and 14 days after they are bitten by an infected mosquito. The symptoms, some of which resemble a cold, can include fever, headache, and body aches, nausea, vomiting, and sometimes swollen lymph glands or a skin rash on the chest, stomach and back.  The symptoms can last anywhere from a few days to several weeks--even in seemingly healthy people. 

In a very few cases (1 in every 150 cases), the symptoms will be severe.  These can include high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis. These symptoms may last several weeks, and neurological effects may be permanent.


How is it spread?

In most cases, West Nile Virus is spread by an infected mosquito to a bird which travels or migrates.  The bird in turn gets bitten by an uninfected mosquito, which then carries the virus to other birds.  As you can see in the illustration below, those infected mosquitoes will occasionally bite other hosts such as horses and people, and transmit the virus to them.  Contrary to some rumors, you can't catch the disease from casual contact, such as touching or kissing an infected person.

What is the treatment for West Nile Virus?

There is no specific treatment for WNV infection. In cases with milder symptoms, people experience symptoms such as fever and aches that pass on their own. In more severe cases, people usually need to go to the hospital where they can receive supportive treatment including intravenous fluids, help with breathing and nursing care.

Who is at risk?

The main people who are at risk of developing severe symptoms are people aged 50 and over, as well as those people who have compromised immune systems as a result of disease or drug treatment programs.  It should also be noted that if you spend a lot of time outside, your risk factor goes up sharply.

What we are doing...

The Alameda County Mosquito Abatement District is very concerned about West Nile Virus. Since its appearance in the state and county, we've taken numerous steps to combat the spread of the virus. Some of these are:
  •  Hiring seasonal help to increase our larval surveillance program, and to treat storm drains and catch basins.
  •  Increasing the trapping of adult mosquitoes for disease testing and population evaluation.
  •  Providing increased training for all our employees.
  •  Participating in a state-wide dead bird surveillance program (call 1. 877. WNV BIRD if you find one).
  •  Increased public's awareness and education about WNV.
  •  Coordinating our response plan with other agencies.

What you can do...

There are many things that homeowners and residents of the county can do to make their homes and properties less welcome to mosquitoes. Mosquitoes need water to complete their lifecycle, so if you can eliminate standing water on your property, we will be ahead of the game! The following are suggestions to prevent mosquitoes from breeding near your home and decreasing the chances of being bitten by them:
  •  Report a dead bird or squirrel - call 877-WNV-BIRD (877-968-2473)
  •  Stock your fishpond with free mosquitofish from us
  •  Eliminate all standing water on your property, and ask your neighbors to do the same
  •  Screen your windows and doors, and make sure they fit tightly
  •  Minimize outside activity at dawn and dusk
  •  When outside for extended periods, wear long sleeve shirts and long pants and use insect repellent (follow label directions carefully)
  •  Keep outside lighting to a minimum near entry doors (some mosquitoes are attracted to lights)

Good News for Horse Owners!

There are available vaccines for horses against West Nile virus. Contact your local vet for more information.

Go to Downloadable Documents for WNV brochures


More information on West Nile Virus...

Center for Disease Control--California
CDC (Centers for Disease Control and Prevention):  The direct link to the CDC's webpage regarding the West Nile Virus.
CDPH:  The California Department of Public Health
California Vectorborne Disease Surveillance System:  A cooperative effort by UC Davis, the Mosquito and Vector Control Association of California, and the California DPH.
California West Nile Virus Surveillance Information Center:  The state government's page on the West Nile Virus.
CDFA--Animal Healthcare--West Nile:  The California Department of Food & Agriculture's page on the West Nile Virus--an excellent resource for horse owners.
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