West Nile Virus Mosquito Species of Contra Costa County

The Culex pipiens (commonly known as the House Mosquito) and Culex tarsalis (commonly known as the Western Encephalitis Mosquito) are the two species of mosquitoes responsible for acquiring and transmitting West Nile virus in Contra Costa county.

imageWhat does a Culex pipiens mosquito look like?

The Culex pipiens mosquito is considered to be a medium-sized mosquito, the adult Culex pipiens may reach up ¼”. The House mosquito species' body is usually brownish or grayish brown. The proboscis and wings are usually brown.

What does a Culex tarsalis mosquito look like?

The Culex tarsalis mosquito is a black mosquito distinguished by a white band on its proboscis, as well as white bands on its tarsal joints. It also has white longitudinal stripes extending along the middle and hind legs, and dark chevron patterns along the underside of its abdominal segments.

What is West Nile virus?

West Nile virus is an arbovirus (transmitted by mosquitoes) that begins primarily in certain species of birds. When infected birds are bitten by mosquitoes, the mosquitoes then acquire the infected blood and are able to spread the virus by biting other birds, people, or some mammals (especially horses).

What are the symptoms of West Nile virus?

Most people (about 80 out of 100) who become infected with West Nile virus do not develop any symptoms.

Some people however (about 20 out of 100) can develop moderate symptoms of the virus (known as West Nile fever). Symptoms of this form of West Nile virus can include headache, fever, body aches, and a rash. Recovery from West Nile fever can take days, weeks, or even months.

The severe form of West Nile virus (encephalitis or meningitis - inflammation of the brain or surrounding tissues) can impact 1 out of 150 people and can result in permanent damage to the body or even death. Symptoms include headache, high fever, neck stiffness, coma, and paralysis. People with pre-existing medical conditions, such as cancer, diabetes, hypertension, and kidney disease are at greater risk for this severe form of the virus.

Is there a cure or vaccine for West Nile virus?

No vaccine or specific antiviral treatments for West Nile virus infection are available. Over-the-counter pain relievers can be used to reduce fever and relieve some symptoms. In severe cases, patients often need to be hospitalized to receive supportive treatment, such as intravenous fluids, pain medication, and nursing care.

How can I protect myself from West Nile virus?

The most effective way to avoid West Nile virus is to prevent mosquito bites.

  • Use insect repellents when you go outdoors. Repellents containing DEET, picaridin, IR3535, and some oil of lemon eucalyptus and para-menthane-diol products provide longer-lasting protection. To optimize safety and effectiveness, repellents should be used according to the label instructions.
  • When weather permits, wear long sleeves, long pants, and socks when outdoors. Mosquitoes may bite through thin clothing, so spraying clothes with repellent containing permethrin or another EPA-registered repellent will give extra protection. Don't apply repellents containing permethrin directly to skin. Do not spray repellent on the skin under your clothing.
  • Take extra care during peak mosquito biting hours. Take extra care to use repellent and protective clothing from dusk to dawn or consider avoiding outdoor activities during these times.
  • Install or repair screens on windows and doors to keep mosquitoes outside.

How can I prevent Culex pipiens or Culex tarsalis mosquitoes?

Help reduce the number of mosquitoes around your home by emptying standing water from flowerpots, gutters, buckets, pool covers, pet water dishes, discarded tires, and birdbaths on a regular basis. Be sure swimming pools and ornamental ponds are filtered and properly maintained. Do not over-water lawns or landscaping since standing water in catch basins will contribute to mosquito production.

Residents of Contra Costa County can also contact the District by phone to report neighborhood mosquito problems or to request a free inspection: (925) 685-9301 or make an online service request.

Return to Top