Mosquitoes that transmit yellow fever, Zika found in Contra Costa County

Yellow fever, dengue Fever, Zika, those are serious diseases that usually occur in far-away tropical environments, but Contra Costa County officials sounded the alarm that the mosquitoes that transmit these viruses have been found in the area.

Now, they're preparing a major offensive to try to kill them before they begin hibernating for the winter.

"We have found invasive mosquitoes in Antioch, and it's the species aedes aegypti, which is the yellow fever mosquito," said Contra Costa Vector Control District G.M. Paula Macedo. "This is not a mosquito that we've had here before."

The Aedes aegypti, with their black and whites stripes, are known as "ankle biters" because they usually attack the lower part of a person's leg.  And they're pretty small, about the size of a grain of rice. But their biology allows them to carry some big-time diseases, including Yellow Fever and Dengue.

Normally, the county sees only a few cases a year, in people who have traveled to other countries.

"If we have people that are carrying Dengue, and this mosquito bites the right person, they can transmit it to someone else," said Macedo.  "So, if that happens, we call it a 'locally acquired case.' And that's what we don't want because it can start an epidemic in the area."

On Saturday, Vector Control District officials held an informational meeting at a park in the infested area. The boundaries extend from Highway 4 to the north to Blue Rock Drive to the south to Lone Tree Way to the west and Deer Valley Road to the east. Crew members have been blanketing the area, searching in front and backyards for breeding sources, such as old tires.

"They do collect rainwater, and these invasive species will lay their eggs there," said an inspector examining the backyard of a home in the area.

But an unmaintained swimming pool in the same backyard was a more serious breeding ground. It took only one scoop into the filthy water to turn up mosquito larvae.

The district can treat sources like that to kill the developing larvae, and beginning Tuesday, weather permitting, they will begin fogging the neighborhoods with trucks to spray mosquito-killing bacteria over houses and into backyards.

Back at the park, Kimberly Born arrived with some concerns about that.

"I have two koi ponds in my backyard, and my concern was the spray, whether or not I need to cover my ponds or not," she said, before getting the answer she was hoping for. "And whatever they're spaying is not harmful to animals or aquatic life. So, I'm a happy camper."

As she stared at a beaker full of swimming larvae, 8-year-old Brooke Mann explained why a lot of people may be breeding mosquitoes without realizing what they are.

"They're wiggly. They look like tadpoles but smaller," she said.

It's a serious threat and the district said it will be spraying the neighborhoods because there is a short window to kill the mosquitoes before cooler weather puts them into hibernation.

"Kind of like the Medfly was many decades ago, I'm sure people will freak out about it," said resident Ken De Silva. "But, you know, the alternative is we have yellow fever or Zika or something."

And the county isn't taking "no" for an answer.

"In the end, the house that didn't let us in, we're going to go for a warrant with code enforcement to come in," said Macedo. "We will come in, no matter what. So, if you let us in now or two weeks from now with code enforcement, it's going to be your choice. But we have the right as a public health agency to do this, to protect public health."

Aedes aegypti are well-adapted for survival. Their eggs can survive six months after the water source has dried up. Southern California has been battling the mosquito for a few years now, and so far this year they've had six locally-aquired cases of Dengue in Los Angeles and one in San Diego.

In the Bay Area, they showed up two years ago in Martinez, but eradication was successful.

"Here (in Antioch), the area is much more widespread and I'm very concerned," said Macedo.

So, officials are scrambling to kill as many as possible now, before the weather begins to warm up in April and the population has a chance to really take off.