zika mosquitoWorries over the Zika virus hit home last week with the devastating announcement that two California babies were born with microcephaly, even as Florida began aerial spraying to counter the spread of the first U.S. outbreak.
The types of mosquitoes that transmit Zika elsewhere are scattered throughout Southern California, although so far none have tested positive for the virus or been linked to a human case.
Here is what public health and mosquito experts know about the risk here: How widespread is the disease?
Q A California has reported 134 travel-associated Zika virus infections in 23 counties, including 23 cases in pregnant women. Los Angeles County has 29 cases, including nine pregnant women. Orange County has 10 cases; San Bernardino County has seven and Riverside County has three.
How likely are mosquitoes to spread Zika in Southern California?
A The chance is low but certainly possible, said Dr. Vicki Kramer, chief of vectorborne diseases for the state Department of Public Health. The two nonnative species that can carry Zika — yellow fever and Asian tiger mosquitoes — both bite during the day. They have been found in parts of Los Angeles, Orange and San Bernardino counties. Riverside County has only had the yellow fever mosquito, which is the most likely of the two to transmit Zika. “We do anticipate the abundance of distribution will continue to increase,” Kramer said. “We are at the peak time of year when these mosquitoes are active.” If transmission does occur, it is expected to be limited in range as has so far been the case in Florida.
“These mosquitoes just don’t fly very far,” said Jared Dever, spokesman for Orange County Mosquito and Vector Control District. “They are perfectly happy completing their life cycle, including feeding on humans, in a single backyard.”
Q How are Zika strike forces working to knock out the mosquitoes?
A After a traveler tests positive for Zika, vector control workers visit the patient’s neighborhood to search for mosquitoes, test them for the virus and eliminate breeding sources.
Neighbors are also provided with educational material in multiple languages. One challenge, however, is that the yellow fever and Asian tiger mosquitoes are not dependent on standing water to breed, unlike the mosquito that transmits West Nile virus, Dever said. Mosquitoes that carry Zika can lay eggs in empty containers, such as a gardening pot, and survive for more than six months until rainfall.
Q Will travelers returning to Southern California from the Olympics accelerate the number of Zika cases?
A It’s winter in Brazil and mosquitoes are less prevalent, so the threat of transmission is considered less likely than from Latin American countries located in the Northern Hemisphere.
In Los Angeles County, for instance, most of the Zika cases have been diagnosed in travelers returning from Honduras, El Salvador and Guatemala, said Dr. Ben Schwartz, acting director of the acute communicable disease control program for Los Angeles County’s Department of Public Health.
“Probably the greatest risk is in those who go back and forth to those countries to visit friends and family who may live in villages where there isn’t air conditioning or screens on windows,” Schwartz said. “For people who are traveling to Rio and staying in hotels with air conditioning, I think the risk is probably less.”
Q What is being done here to monitor pregnant women with Zika?
A Schwartz said once a pregnant woman tests positive, she and her obstetrician are briefed on the illness and potential risks to the unborn baby. Upon birth, testing is done to see if the infant is infected.
Dr. Karen Smith, state health officer, said the infants born with microcephaly, which is characterized by an abnormally small head and typically underdeveloped brains, will be monitored for the first year of life. They will be tracked not only for neurological problems but for hearing, vision and other developmental issues.
“We’re not just following infants who clearly have birth defects, we’re going to be following infants who appear normal at birth,” Smith said.
“There’s a lot we don’t know about the full spectrum of what Zika gained congenitally could cause.” For more information visit www.cdph.ca.gov

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