While a case of Zika virus was reported in California this week, health officials say the state’s dry Mediterranean climate and pest control efforts make it an unlikely home for the mosquitoes that carry the tropical disease.
Two species of Aedes mosquito can transmit the virus, but neither is found in high concentrations in California. Some mosquitoes, however, have been detected as far north as Hayward and Menlo Park in the Bay Area and in Central Valley cities such as Madera, Fresno and Clovis. The mosquitoes have been found in the greatest numbers in Southern California, particularly near the U.S.-Mexico border, said local mosquito control officials.
Most people who contract Zika virus don’t even know it – only one in five people show mild symptoms such as fever, rashes and joint pain, and few end up hospitalized. But since the global Zika outbreak began in Brazil last spring, about 4,000 babies have been born with microcephaly – a serious neurological birth defect that makes an infant’s head abnormally small and causes brain damage. Disease experts suspect mothers are transmitting the virus to babies during pregnancy, and officials in El Salvador and Brazil have advised women not to conceive until the outbreak abates.
The virus is active only during the first week after infection, and can only be transmitted from person to person via mosquito bite. An adolescent girl in Los Angeles County who traveled to El Salvador last year was diagnosed with the virus but recovered. Officials expect more Zika cases will appear as people travel to and from affected countries. In Hawaii, a baby with microcephaly was born to a mother who had recently visited Brazil. There has not been any Zika transmission reported within the United States.
Researchers are still looking into the exact cause of the strange birth defect. There are not currently any vaccines or treatments for the virus.
“The relationship between the virus and the mosquito is very specific,” said Matt Baur, associate director of the federally funded Western Integrated Pest Management Center. “It’s a pretty tight link, and it would be unusual for it to jump into another mosquito and be as competent.”
The striped, aggressive Aedes mosquitoes are known for attacking during the day. They thrive in humid climates and tend to breed in standing water. They’re also responsible for spreading tropical diseases such as dengue and chikungunya, which have not been major problems in California.
No Aedes mosquitoes have been detected in Sacramento and Yolo counties in the last five years, said Luz Maria Rodriguez, spokeswoman for the Sacramento-Yolo Mosquito & Vector Control District. Still, there is always a chance the mosquitoes will migrate. Her department is always on the lookout for the exotic insect, and encourages anyone who spots or gets bitten by one to report the incident immediately.
“It would be easy for them to make their way over,” she said. “They’re very prolific backyard breeders, and they like to breed in common household containers like potted plants or a bit of water. All it would take would be someone relocating from So Cal to our area and bringing their potted plants with them, that’s how they’d move in.”
People can keep their homes free from mosquitoes by dumping out standing water, closing windows and cleaning their gutters, bird baths and pet bowls.
In response to the global outbreak, the U.S. Centers for Disease Control and Prevention has issued travel warnings for pregnant women and women trying to conceive, suggesting they postpone any planned travel to areas where Zika virus transmission is ongoing. The California Department of Public Health followed suit this week with its own warning.
Expectant mothers who already have trips planned to affected regions may want to consider other destinations, said Dr. Dean Blumberg, chief of pediatric infectious disease at UC Davis Children’s Hospital.
If women do travel to areas where the virus is rampant, they should take special care to avoid mosquito bites, even if it means staying indoors during the day. They should also use Environmental Protection Agency-approved insect repellants, which Blumberg said are safe for use while pregnant.
“There’s enough to worry about when you’re pregnant about what to eat and what you might be exposed to, and here’s one more thing that could have an adverse effect for the newborns,” he said.
There may be more people traveling between the U.S. and Brazil due to the upcoming Carnival holiday and the 2016 Summer Olympics in Rio de Janeiro.
Since 2013, visitors from Central America (excluding Mexico) to California have increased by 54 percent, and visitors from South America have grown by 9 percent, according to a 2015 California Office of Tourism report.
State and Sacramento County health officials are asking physicians to stay on the lookout for people who have recently traveled from Zika-affected areas by asking patients, especially those with fevers, about their travel history.
Dr. Jorge Parada, medical advisor for the National Pest Management Association, said he expects to see the most Zika transmission in Southern U.S. states with gulf climates. Though California will likely see travel-associated cases, he said he doesn’t expect many local infections.
“Nobody needs to freak out,” Parada said. “As a health system, I think the CDC and other entities are correct to have their antennas up for any cases. ... The caveat is if it does start having local transmission, things can turn very quickly. Mosquito control isn’t easy.”