Yellow Fever Mosquitoes In California, Texas, Arizona


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The yellow fever has been discovered in California mosquitoes. Image by forbiddenarts.

Researchers have discovered yellow fever in California mosquitoes. Image by forbiddenarts.

Mosquitoes are annoying and cause itchy bumps, but generally, here in the United States, that is all we have to worry about.

However, people are viewing mosquitoes in California, Texas, and Arizona a bit differently now that researchers have found that some are capable of carrying yellow fever.

Researchers spotted the Aedes aegypti, a type of mosquito that is capable of carrying yellow fever and dengue, along with other diseases, in California’s Central Valley communities of Madera and Clovis this past June. Since, they’ve found these dangerous bugs in San Mateo County in the Bay Area, as well as locations in Arizona and Texas – and they’ve now found them in Fresno as well.

Yellow Fever Mosquitoes

So why the cause for concern? The bite of these mosquitoes means the potential for spreading deadly diseases. Yellow fever is a virus that we generally find in the tropics and subtropics in South America and Africa. The virus transmits to humans via the Aedes aegypti mosquito. If a mosquito bites the infected person, that mosquito can carry the virus to the next person it bites.

According to the World Health Organization, the first phase of yellow fever is known as the ‘acute’ phase and is not fatal. Patients with the acute phase generally recover within three to four days. However, according to the WHO, 15 percent of patients in the acute phase will develop a more severe case within 24 hours of the first remission. Patients in this more severe phase of yellow fever may experience high fevers, and rapidly develop jaundice, abdominal pain, nausea, and vomiting. They can also bleed from their nose, mouth, eyes and stomach – and half of them will die, most within two weeks.

Preventing and Treating Yellow Fever

Unfortunately, there is no treatment for yellow fever, only supportive care to treat the symptoms, but there is a yellow fever vaccine for infants older than nine months, children, and adults. The vaccine provides life-long immunity against yellow fever within seven to ten days for 95 percent of the people who receive the vaccine. To prevent outbreaks, health officials recommend that the majority of a population receive the vaccination.

We can control mosquitoes, the carriers of the disease, however. Eliminate the breeding grounds of mosquitoes, like standing water, and applying insecticides to the water can cut short the circle of life for the species. According to CBS News, the California Department of Public Health is spraying promethean around homes – however, according to information in the California mosquito-borne virus prevention plan, they’re likely using permethrin, a low-risk pesticide often used to kill mosquitoes.

No one showing up to spray your home? You can also reduce your chances of getting bitten by wearing long sleeves and pants, and applying insect repellent.

Mosquito Concerns

No one in the United States has contracted yellow fever, and researchers have not yet trapped a mosquito carrying the disease. Our biggest danger is that someone with Yellow Fever could enter the United States, and start a chain reaction. Take precautions by emptying any standing water that may be in your yard, protecting your skin by using an insect repellent and/or wearing long sleeves and pants to prevent bites, and you can reduce your chances of getting this, or any other, mosquito-borne illness.


California Health and Human Services Agency. Yellow Fever Mosquito (Aedes aegypti) Fact Sheet. (2013). Accessed October 22, 2013.

EPA. Permethrin Facts (Reregistration Eligibility Decision (RED) Fact Sheet). (2013).  Accessed October 22, 2013.

National Pesticide Information Center. Pesticides Used in Mosquito Control. (2013). Accessed October 22, 2013.

CBS News. Yellow fever mosquito found throughout California. (2013). Accessed October 22, 2013.

Centers for Disease Control and Prevention. Yellow fever, symptoms and treatment. (2011). Accessed October 21, 2013.

World Health Organization. Yellow Fever. (2013). Accessed October 21, 2013.

Brown, E. California Mosquito-Borne Virus Surveillance & Response Plan. (2013).  Accessed October 22, 2013.

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