[thedoc (OP)]

Margaret Lee asked the Naked Scientists:
   My daughter is going to work in Brazil next year, and I would like to ask (because I don't know where else to go) if she does catch the Zika virus, how long will she be capable of carrying the virus in her bloodstream to have mosquitoes carrying her blood infect others?
What do you think?

[evan_au]

Recent (September 2016) advice from the US Centers for Disease Control (CDC) recommends that women avoid starting a pregnancy for at least 8 weeks after possible exposure to Zika virus. For men the recommendation is 6 months.

This is based on the continued ability to detect viral RNA after the cessation of symptoms (although many cases of Zika have no detectable symptoms)

See: https://www.cdc.gov/mmwr/volumes/65/wr/mm6539e1.htm

[chris]

In the UK we are using the same guidance, at the moment. Specifically, women should wait at least 8 weeks after a potential exposure (regardless of whether symptomatic) while men should wait 6 months (also, regardless of whether symptoms have occurred).

The reason for the difference is that there are certain sites in the human that sit beyond the reach of the immune system and can act as reservoirs for infection. The testis is one such site, the eye is another. The immune system is excluded here, but virus particles, which are tiny in comparison with one of our cells, can gain access during the acute phase of the infection and then persist in these sites for a variable amount of time afterwards.

As the case load of Zika increases, so the opportunity to monitor this persistence effect; on this basis, using detection of the viral genetic information (RNA), the current guidelines have been established; However, detection of RNA is not the same thing as genuine infectivity; a virus does not need to be intact and infectious for its genetic information to be detectable using modern, high sensitivity nucleic acid amplification tests. The 6 months that is advised is therefore a cautious guideline with a healthy safety factor built in.

[evan_au]

Also, pregnant women (or women who have not been taking precautions against pregnancy) should avoid travel to Zika-prone areas.

If travel is unavoidable, take precautions such as mosquito repellent, clothes that cover arms and legs, avoid being outdoors near dawn and dusk, and use bed nets at night.