Health, vector officials gird for battle against Zika virus
Disease is here to stay, experts say. No. 1 priority: Control mosquito population.
Jason Farned set down a clear container in the middle of a table. The people gathered around leaned forward to peer at the tiny, zooming blurs trapped inside.
“The deadliest creature in the world is the mosquito,” said Farned, who works for the San Gabriel Valley Mosquito and Vector Control District, a government agency that manages insect populations. By some estimates, mosquitoes transmit diseases that kill more people each year than any other creature.
The ones Farned brought to this recent meeting in El Monte were Aedes mosquitoes — the kind that spread Zika virus, the disease discovered last year to cause birth defects.
Though no one has contracted Zika virus from a mosquito in California, hundreds of people have been infected in other countries and then returned to the state. All it would take for the disease to start spreading here is for an Aedes mosquito to bite an infected traveler and then another person, experts say.
It’s been a year since the World Health Organization declared Zika an international public health emergency, but officials are still far from eliminating the virus. Winter has slowed its worldwide spread, but rising temperatures in the spring are bound to bring more cases.
And because a vaccine won’t be ready for years, California mosquito-control and health officials are making plans to battle Zika every summer for the foreseeable future.
Though “we’re able to adjust to the new normal that now includes Zika ... we have to remember that there are people behind the statistics — babies, pregnant women,” said Dr. Edward McCabe, chief medical officer for the March of Dimes. “We cannot let down our guard.”
The first line of defense against Zika is mosquito control, officials say.
The disease is transmitted only by Aedes mosquitoes, which aren’t native to the Americas. The insects showed up in El Monte in shipments of bamboo from Southeast Asia about 15 years ago. The local vector control agency assigned seven people to work full time to try to get rid of the incredibly resilient bugs, Farned said.
“No community anywhere on the planet has successfully been able to eradicate them. We were really trying to be the first,” he said. “They’re pretty much here to stay.”
The mosquitoes are now found in 12 counties in California, with particularly dense infestations in the San Gabriel Valley.
Farned has enlisted the help of the Buddhist organization Tzu Chi to try to spread the word about Aedes mosquitoes. The El Monte meeting included a dozen volunteers who collectively spoke Mandarin, Cantonese, Malay and Vietnamese in addition to English.
Part of the reason Aedes mosquitoes are so intractable is because spraying pesticides doesn’t work on them as well as it does on the Culex mosquitoes that Californians are more familiar with, officials say.
The only tactic that’s proved successful in curbing Aedes populations is sending workers door-to-door to check every home for standing water. It’s a tedious task, because Aedes mosquitoes can breed in “anything from a bottle cap to a Jacuzzi,” said Gimena Ruedas, an assistant vector ecologist with the San Gabriel Valley vector agency.
The insects need only a few drops of water to reproduce and can even survive inside people’s homes. Their eggs can tolerate months of drought, waiting for rain to hatch.
On a recent morning, Ruedas and her colleague Javier Romo scoured backyards in East Pasadena searching for the mosquitoes and their eggs, which are barely visible to the human eye. Ruedas and Romo are called when homeowners notice the small mosquitoes, usually because they were bitten in the daytime, characteristic of Aedes.
The two looked inside storm drains and fountains and shone flashlights on the lips of upturned pots. Any pool of water as big as a teaspoon could be a danger. Ruedas said she once saw mosquitoes breeding in water droplets collected in a dried-up leaf. “We cannot go to every single house and look for every single bottle cap,” Ruedas said.
Pilot projects in El Monte and the Central Valley have tried to curb mosquito populations by releasing male Aedes aegypti that are infected with bacteria that prevents their eggs from hatching. The efforts had positive results, but these new methods will probably require federal approval and take several months before they’re widespread.
Officials say that at the very least, the attention around Zika virus has made people more aware of the invasive mosquitoes, which can also transmit deadly diseases such as dengue and chikungunya. Vector control agencies had been sounding the alarm about Aedes mosquitoes since they arrived in California, but didn’t get much traction until Zika came on the scene.
The Zika outbreak began in Brazil last year but then spread to dozens of countries, including the United States. Mosquitoes in parts of Florida and Texas began transmitting the virus.
That has yet to happen in California, which doesn’t have such high mosquito populations. But there is a lot of travel between California and countries with outbreaks, such as Mexico and Guatemala, which increases the risk; 479 Californians have contracted Zika elsewhere, and three babies in California whose mothers were infected with the virus have been born with birth defects.
The Los Angeles County Department of Public Health is setting up surveillance sites at clinics in local areas that could be susceptible to an outbreak, including the San Gabriel Valley and East L.A., said the department’s Dr. Rachel Civen. If patients show up with Zika symptoms, they would be encouraged to get tested, she said.
Still, it would probably take a while for officials to find out if there were an outbreak in California. Zika symptoms are usually too mild to make someone seek out medical treatment, and only 20% of those infected have symptoms at all. Many people would have to get Zika before one of them was sick enough to go to a doctor to be tested, she said.
Zika virus has kept health officials on their toes across the country. Most doctors had never heard of the virus before last year, and information about the virus rapidly evolves. Since the early reports linked Zika to microcephaly, scientists have discovered that the primarily mosquito-borne virus can also be sexually transmitted, cause the Guillain-Barre neurological disorder and also damage adult brains.
“It’s pretty stressful — things are not ideal,” Civen said. But the constant stream of new findings means health officials are able to provide up-to-date recommendations to help keep people safe, she said.
Civen said it’s too early to know whether a case of Zika will eventually occur in L.A. It depends on the weather and how big the outbreaks will be in other countries this year. Regardless, a different threat could be around the corner, she said, especially considering how much people travel globally.
“It may not be Zika, it may be some other virus,” she said.