Science Questions

How long does zika remain active?

Mon, 8th Aug 2016

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Steven Mushkat asked:

Hi Chris and team, your podcasts are terrific! I especially like your Q&A episodes. This time around I do have a question. We've heard how the Zika virus is a risk to pregnant women - but how long does the virus remain active for women who might become pregnant? Is that something to be concerned about, contracting the virus today, and having to worry about the pregnancy in five years time? Or is that enough time for the body to fight off the virus? Same question for men as well as potential carriers.


We put this to Naked Scientist, Chris Smith...Zika virus Electron Micrograph

Chris - Yes, these are all really pertinent questions, which we donít actually have gold standard answers to yet. But it is a big problem and, based on the paper from Andy Tatumís group at Southampton last week in Nature Microbiology, theyíre saying that 93 million people are going to get infected with Zika in the next two years in the Americas, and there'll be 1Ĺ million women who are currently bearing children in that group of individuals. So thereís going to be a lot of exposures going on and those are people who catch it when they are pregnant.

Now we know thatís a risk because when you have virus in your bloodstream, it can get across the placenta, which is normally a very good barrier and stop it getting in.  But, with this virus, it can cross the placenta and it homes in on the stem cells that make your brain, as well as other tissues, and it damages those stem cells. So thatís why it causes harm to a developing baby.

The thing people are really worried about is whether or not it can lurk in the body and stay there so that, although youíve cleared the virus, you could succumb later or your pregnancy could be harmed. The evidence is that if youíre female, you catch Zika, your immune system kicks in, it kicks it out and you clear it after a week or so, and you do not have any virus thatís going to cause a subsequent pregnancy with any problems because it would have to get across the placenta from the blood and thereís no virus in the blood.

Where the threat comes from is that your partner could, if he catches Zika virus, retain virus in certain body fluids for an extended period of time. We know that there have been sexually transmitted cases of Zika, anything up to several weeks after the person stopped having any symptoms or any virus in their bloodstream. So the worry is that people could think that theyíre actually fit and healthy and theyíve recovered from it. Or they may not even have had any symptoms of Zika in the first place because 80% of people donít even know theyíve had it, and then you transmit it to your partner, she catches it and she then gets the virus in her bloodstream and it then goes into the baby. We donít think thereís any risk of the virus going from the genital tract directly up into a baby.

Kat - I think itís probably best just never to have sex again!

Chris - Well... Iíll leave that one to you Kat.


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