Stanford Medicine Newsletter Updates For the Local Community


What to know about Zika virus

Desiree LaBeaud, MD, focuses on understanding the risk factors and long-term health consequences of infectious diseases like the Zika virus.


The warm weather of summer is an invitation to mosquitoes, which may carry the risk of disease, such as Zika virus. Desiree LaBeaud, MD, is a Stanford pediatrician and infectious disease researcher who focuses on understanding the risk factors and long-term health consequences of arboviral infections, including Zika. She spoke with Stanford Medicine News about the local risks of Zika, what precautions residents can take, and what travelers should do to avoid infection with the virus.

Q: What kind of risks could Zika pose this summer to Bay Area residents?

LaBeaud: While there is currently a minimal risk of Zika virus spreading to the Bay Area, there are a number of factors that could contribute to a local outbreak. The vector that transmits Zika virus and many other viruses is Aedes mosquitoes. Aedes mosquitoes have been found in many areas of California, including Menlo Park, Atherton, San Mateo and Hayward. Without exposure to the virus, these mosquitoes cannot transmit Zika virus.

People returning from summer vacations in areas of South and Central America or the Caribbean may have been infected with Zika virus without experiencing any symptoms. There is a very low risk of a recent traveler starting an outbreak in the Bay Area. The traveler would have to have an active infection, which occurs within two to seven days after being bitten by an infected mosquito, and would have to be bitten by an Aedes mosquito in the Bay Area. The Aedes mosquito density is much lower in the Bay Area than it is in South and Central America and other tropical regions of the world. Also, we spend more time indoors here, decreasing outbreak risk. If there were an outbreak locally, county officials would likely monitor it and keep the public informed of needed precautions and developments.

Q: Are there specific precautions people should take to protect themselves from the virus?

LaBeaud: The Centers for Disease Control and Prevention suggests avoiding travel to areas affected by the current outbreak. For people planning on travel to Latin America or the Caribbean, we highly suggest mosquito repellent. Pack clothing with adequate coverage (long sleeves and long pants), treat your clothing with mosquito repellent (like permethrin) before traveling, and apply mosquito repellent (DEET, picaridin) liberally and often. Avoiding the mosquito vector is your best chance of minimizing your risk of infection.

If you are concerned about being exposed at home despite the low risk, survey your house and yard for containers that collect water. Standing water in small containers — flowerpots, bird baths, garden fixtures, children’s toys or play structures, for example — is the preferred environment for Aedes mosquito breeding. Dumping out standing water will reduce mosquito breeding around your home.

LaBeaud says travelers to Latin America or the Caribbean should take extra precautions to protect themselves from Zika virus and avoid mosquito-infested areas.


Q: What are the health risks associated with Zika?

LaBeaud: Typically, Zika virus can cause a broad range of symptoms that have been described as “dengue-like syndrome.” Symptoms may include fever, headache, rash, muscle and arthritic joint pain, conjunctivitis (red eyes) and eye pain. These symptoms are usually mild and last a few days. About 80 percent of people who have been infected experience no symptoms, though symptoms may be worse in children or people with compromised immune systems.

The CDC is conducting an extensive investigation to determine whether microcephaly in newborns — children born with unusually small brains — and a severe neurologic disorder known as Guillain-Barré syndrome are linked to Zika virus and what may increase a patient’s likelihood of experiencing these serious problems. During a previous Zika virus outbreak in French Polynesia, the incidence of Guillain-Barré syndrome increased 20 times.

Some researchers believe that people in these regions may have a genetic or physiological susceptibility to a more severe form of Zika disease. Others believe that the strain of virus that is causing the current outbreak has mutated to be particularly virulent. Another thought is that previous exposure or co-infection with another virus, such as dengue virus, that is endemic in currently affected regions may increase the risk for severe Zika disease.

Q: Are there Zika-prone areas of the world that travelers should avoid?

LaBeaud: Zika virus transmission was documented in a total of 57 countries and territories. The current outbreak has been reported in 33 countries across South and Central America and throughout the Caribbean islands. Brazil has experienced a significantly large outbreak since May 2015. Six countries (Argentina, Chile, France, Italy, New Zealand and the United States) have reported locally acquired infection through sexual transmission. Vietnam is the most recent to report mosquito-borne Zika virus transmission.

Q: What makes certain species of mosquitoes such powerful transmitters of Zika?

LaBeaud: Aedes mosquitoes, specifically Aedes aegypti and Aedes albopictus, are the vectors for Zika virus and many other viruses. The female mosquitoes take blood meals from larger mammals to stimulate the development of eggs. These mosquitoes are anthropophilic, which means they prefer to feed on people. They bite during the day, making people more susceptible to bites.

Aedes mosquitoes breed near the home environment, where often there are objects with small amounts of rainwater or pooled water, such as tires, containers used for water collection, empty planters and bowls. Breeding near the home makes them more likely to bite humans, as they do not need to travel far for a blood meal.

Aedes aegypti females are nervous feeders, so any movement during feeding will make them fly off. This means that it takes an average of four or five human feedings for them to have a full blood meal to lay eggs, and the mosquito can infect during all of them. That means she can transmit viruses very efficiently.

Q: There is some intensive research underway to characterize the virus and its impact on humans. What have been some of the most important developments thus far?

LaBeaud: The most pressing research investigations on the current outbreak in South and Central America have focused on determining whether or not infection with Zika virus is causing the increased incidence of microcephaly or Guillain-Barré syndrome.

Additionally, there is a large effort to develop faster and more accurate diagnostic tests, which will help monitor the spread of the outbreak without any laboratory lag time.

Research investigating the characteristics of the virus and mechanisms involved with the host immune response will assist with the development of a potential vaccine and targeted therapeutics. There is a lot that needs to be done to characterize the true impact of Zika virus, determine the spectrum of disease resulting from infection, and prevent or treat maternal Zika virus infections.

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