Zika virus: Common questions about the mosquito-borne virus

We asked our experts about the virus that is making headlines for its rapid spread.
March 1, 2016

With the Zika virus making headlines for its rapid spread throughout South and Central America, Mexico, Puerto Rico and the Caribbean, we asked the experts to answer common questions about the mosquito-borne virus.

Question: What is the Zika virus?

Answer: The Zika virus is a flavivirus, which is in the same family as West Nile and Dengue viruses. It was first isolated from primates in the Zika forest of Uganda in 1947 and isolated in humans in 1968. The Zika virus was most likely introduced into Brazil in 2014 and has led to a wide epidemic that is still ongoing.

Q: How do you get the Zika virus?

A: The Zika virus is most commonly transmitted to people through mosquito bites. The most common mosquitos that transmit this virus are Aedes mosquitos, which typically lay eggs in and near standing water and are aggressive daytime biters. It also has been confirmed that Zika virus can be transmited through the semen of an infected male, and there also have been reports of the virus spread through blood transfusions.

A pregnant woman infected with Zika could transmit the virus to her unborn baby during any trimester of her pregnancy, but we don’t yet know if the risk changes at different times during the pregnancy.

Q: If a pregnant woman has traveled to an affected area and is concerned about the Zika virus, what should she do? Should she get tested, and if so, where is the best place to start?

A: Any pregnant woman who has traveled to an area where Zika is currently circulating should talk to her health care provider (OB-GYN or primary care physician) about being tested. Testing should be offered up to 12 weeks after return from travel. The recommended test is a blood test looking for an antibody (IgM) to the Zika virus.

A negative test can rule out a recent infection with Zika virus. A positive test does not necessarily indicate a recent Zika infection, as the test can cross-react with other similar viruses.

Because it can be sexually transmitted, couples in which a man has traveled to an area of active Zika virus transmission should consider using condoms during sex or abstaining from sexual activity for the duration of his partner’s pregnancy.

The CDC may change these recommendations as more information becomes available.

Q: I’ve been told not to worry about the Zika virus if I don’t exhibit symptoms within two weeks of travel. However, if only 20 percent of people have symptoms, what does that mean for the other 80 percent?

A: The other 80 percent have what is called an asymptomatic infection. This means that they have been infected with the Zika virus but did not develop any symptoms. This is a common scenario for a variety of viruses — different people can experience different symptoms (and sometime no symptoms at all) when exposed to and infected with the same virus. Why some people develop symptoms and others do not is not known. At this time, pregnant women should be tested whether or not they have symptoms.

Q: If I am pregnant and become infected with the Zika virus, what impact will it have on my baby? 

A: There have been reports of congenital microcephaly and other birth defects in babies whose mothers were infected with the Zika virus while pregnant, and Zika virus infections have been confirmed in several infants with microcephaly.

It is not known how often microcephaly develops in babies of pregnant women who are infected with Zika. It is also not known if the risk is higher or lower at different times during pregnancy. Studies are currently underway to better understand this association and to see what role other factors might play (such as other prior or concurrent infections, nutrition, and environmental or genetic factors). Since the affected children were only recently born, we also do not have information about long-term effects associated with this congenital microcephaly.

Q: The CDC recommends that all pregnant women suspend travel to areas where the Zika virus is active. But I am pregnant and have an upcoming vacation in an active region. Should I cancel my travel? How serious is this ban? And how long will it last?

A: The safest thing to do until we have more information is to follow the CDC’s recommendation and cancel your trip. If you decide to still travel, you should follow steps to avoid mosquito bites during the trip. It is unknown at this time how long the ban will last.

Q: If I’m not pregnant and don’t plan to be anytime soon, is the Zika virus still something to worry about for me or my children? 

A: Eighty percent of people who become infected with the Zika virus have no symptoms. For the 20 percent who do develop symptoms, the most common findings are fever, rash, joint and muscle pains, headaches and red eyes. Most illnesses with Zika are mild and last for three to seven days. At this time, we don’t have any evidence that a past Zika infection will impact a future pregnancy.

Q: Could the Zika virus spread to Colorado?

A: The Zika virus is not present in Colorado. The climate in Colorado is not ideal for the kind of mosquito that carries Zika, and therefore outbreaks are unlikely to occur here.The Colorado Department of Public Health and Environment has confirmed two Colorado cases of Zika as of June 2, 2016. Both individuals had traveled to a Zika-affected country, and both recovered from the virus. Colorado is likely to have more cases of Zika in the coming year, according to the CDPHE.

Q: Do the mosquitos that carry the Zika virus also carry other viruses that I need to worry about? 

A: The same mosquitos that carry the Zika virus can also carry the Dengue, chikungunya and yellow fever viruses. Over the past few years, Dengue and chikungunya also have been introduced in the Americas with associated large outbreaks and ongoing current transmission.

As with Zika, there are no vaccines or treatments for these viruses, and so prevention from mosquito bites is critical. These viruses have not been associated with causing microcephaly in the babies of infected pregnant women but can cause similar and sometimes more severe disease than Zika.

Yellow fever is endemic in parts of South America and Africa and can cause serious, life-threatening liver disease. Anyone traveling to countries where yellow fever exists should receive the yellow fever vaccine prior to travel.

Q: The World Health Organization has declared the Zika virus a public health emergency. Is this a safety danger for people anywhere in the Unites States? 

A: The mosquitos that carry and spread the Zika virus are found in the southern and eastern parts of the U.S. It is possible that a person returning from a country with Zika transmission could be carrying the virus in their blood and then be bitten by one of these mosquitos in the U.S. This could then cause local spread of the virus. The CDC and local health departments are closely monitoring for this possibility.

Additional resources for Zika virus information:

World Health Organization

Contagious Comments (a newsletter from the Department of Epidemiology at Children’s Colorado that addresses topics related to infectious disease)

About the author

UCHealth is an innovative, nonprofit health system that delivers the highest quality medical care with an excellent patient experience. With 24,000 employees, UCHealth includes 12 acute-care full-service hospitals and hundreds of physicians across Colorado, southern Wyoming and western Nebraska. With University of Colorado Hospital on the Anschutz Medical Campus as its academic anchor and the only adult academic medical center in the region, UCHealth pushes the boundaries of medicine, providing advanced treatments and clinical trials and improving health through innovation.