The Zika virus: A look at where it comes from and how it spreads


The mosquito-borne Zika virus has been making headlines because it may pose a risk to pregnant women.

The Center for Disease Control and Prevention issued a travel alert for anyone planning trips to areas where the virus has been reported, including: Africa, South America, Central America, Mexico and the Caribbean. (See map at right.)

The alert is mainly for pregnant women and those who are trying to become pregnant, and urges them to take extra precautions to avoid mosquito bites or postpone travel if they have plans to visit those areas, the CDC says.

That's because there may be a link between pregnant women who are infected with the Zika virus and microcephaly – a birth defect where a baby has an abnormally small head and brain, the CDC notes.

Microcephaly is typically a rare condition, but there's been an increase in cases in Brazil since the Zika virus was first reported there last year, The Atlantic reports. There were 20 times more microcephaly cases in the South American country in 2015, compared to the year before.

However, the CDC says more research needs to be done to determine if the Zika virus is actually causing these birth defects.

“The question is, is this a new phenomena?” said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, told Bloomberg.

What about people who aren't pregnant?

For those who aren't pregnant, the Zika virus doesn't pose as much of a threat. In fact, four in five people who are bitten by a mosquito infected with the virus have no symptoms, the CDC notes.

For those who do show symptoms, they are usually mild and last from several days to a week. The most common symptoms include: fever, rash, joint pain and conjunctivitis, the CDC says.

But Epidemiologist Elizabeth Schiffman, with the Minnesota Department of Health, told KSTP the virus is something people should know about because "it can make you sick, even if you are only mildly ill."

Could it come to the US?

The virus has spread to dozens of countries since it was first reported in the Western Hemisphere in May 2015, but there have been no reports of people contracting the virus in the United States. 

However, people returning home from known Zika areas have been infected with the disease, the CDC says, and because the outbreak has spread to the Americas, the number of cases among travelers returning to the U.S. is expected to go up.

The CDC says these imported cases of Zika could lead to it spreading locally. If a person who contracted the virus comes back to the U.S. and is bitten by a mosquito, that mosquito could then spread the virus to another person, the CDC explains.

This has health officials asking doctors to check for the virus in people who report similar symptoms upon returning home from areas known to have the virus, and report those cases.

The virus is also moving to new areas when the mosquitoes themselves travel to different countries, either by hitching a ride on travelers or cargo, Osterholm explained to Bloomberg.

How about to Minnesota?

There's some good news for those worried about Minnesota's unofficial state bird spreading the Zika virus – and you can thank our cold winters.

The type of mosquito that transmits most cases of the virus don't live here – the Aedes mosquito likes tropical and subtropical climates, MPR News reports. (Those are the same mosquitoes that spread the chikungunya virus, which made headlines last year.)

Schiffman told KARE 11 the likelihood of someone getting bitten and then coming back to Minnesota and getting bitten again, and then that mosquito biting someone else "obviously could happen," but it's more likely in a place like Florida.

There is one species of mosquito – the Asian tiger mosquito – that is also known to transmit the virus, and infestations of those mosquitoes have been detected in Minnesota in the past, MPR News says. However, Epidemiologist Dave Neitzel told news station there probably aren't enough Asian tiger mosquitoes in Minnesota to really spread the virus locally.

No one from Minnesota has contracted the virus, KSTP notes.

More on the Zika virus

Vox spoke with Scott Weaver, the director of the Institute for Human Infections and Immunity at the University of Texas Medical Branch in Galveston, about how worried people should be about the virus. Read that here.

Vox also has six charts to explain the virus.

The University of Minnesota's Center for Infectious Disease Research and Policy has also written about Zika.

NBC News has published a list of five things you need to know about the Zika virus.

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