Mosquitoes Known to Carry Dengue Fever Seen in California

October 31, 2013

By Steve Gorman

LOS ANGELES (Reuters) Oct 31 - A tropical mosquito known to carry potentially fatal diseases such as dengue and yellow fever has been detected in California, raising concerns among public health officials and prompting intense efforts to eradicate the insect.

No illnesses associated with the mosquito, Aedes aegypti, have been reported since it first appeared in California's Central Valley in June, and none of the specimens trapped and tested has been found to be infected.

But the species' feeding and breeding habits make it a voracious pest, which if allowed to propagate could pose a serious new health threat to the nation's most populous state while diminishing its outdoor lifestyle, authorities say.

The small dark mosquito, distinguished by white markings and banded legs, feeds aggressively during the day, is especially fond of humans, often bites indoors and requires very little standing water to reproduce.

"If it gets established, it's going to change the way we live in California," Tim Phillips, manager of the Fresno Mosquito and Vector Control District, which identified some of the first small invaders, said on Wednesday.

"We're not going to be able to go out on the patio and have a beer or have a barbecue without being eaten up by these things," he added.

How Aedes aegypti was introduced to California remains a mystery. Possible sources include imported potted plants or other small containers with water, Phillips said.

Native to tropical and subtropical regions, the species has already turned up in Hawaii, Arizona, Texas and parts of the U.S. Southeast, Florida in particular.

"We're hoping to eradicate this species, but that will be challenging, and we're certainly interested in whether it can survive the winter months in California," said Vicki Kramer, chief of vector-borne diseases for the state Department of Public Health.

Vector-control authorities in Fresno, Madera and San Mateo counties, where the mosquito has been identified, are warning residents to empty bird baths, dog dishes, flower pots and other sources of standing water from around their homes.


Homeowners are also advised to keep screens fastened over open windows and doors, to apply repellent when outside and to use mosquito netting over infant cribs, carriers and strollers.

Mosquito abatement districts are using special pesticides in places where aegypti is found, but they need help from the public to pinpoint infestations. They say the biggest telltale sign is being bitten in the daytime.

Most mosquito species that are common to residential areas of California tend to feed at night. Others that bite during daylight hours are typically found in rural or undeveloped areas only, officials say.

Aedes aegypti feels very much at home around humans, feeds most often in daylight, and it is a primary vector for both yellow fever and dengue. Moreover, its eggs can survive without moisture for up to two years without hatching, Phillips said.

For now, the risk of contracting either illness in California is low, because a mosquito would have to bite an already infected person then bite another person, experts say.

While there have been locally transmitted human cases of dengue reported in Florida this year, and occasional cases in Hawaii and Texas, all 183 cases documented in California since 2010 have been in people infected while traveling in Latin America, Asia or Africa, Kramer said.

Yellow fever in California is even more rare. The last known case was in 1999, she said.

But the chances of local transmission rise as the incidence of "imported" human cases grows and the Aedes aegypti mosquito population expands.

Dengue causes high fever, debilitating joint and muscle pain, headaches, vomiting and a skin rash. Yellow fever often begins with flu-like symptoms and can progress to a more severe phase that can lead to jaundice and internal bleeding.

Both can be fatal. Worldwide, some 500,000 people with severe dengue require hospitalization each year, and 2.5% of those stricken die, according to the World Health Organization. It estimates the annual number of yellow fever cases worldwide at 200,000, resulting in 30,000 deaths a year.


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