Zika virus: What you need to know

In his first-ever 'Ask Me Anything' session on Reddit, Dr. Isaac Bogoch, Infectious Disease specialist at Toronto General Hospital, UHN, answered questions about the Zika virus.

Here are some of the key questions that came up on the popular discussion forum.

What are your expectations regarding the spread of Zika due to Olympics-related travel?

Dr. Bogoch: This is an issue that has received a ton of attention in the build-up to the Olympics. While there is certainly Zika virus transmission throughout much of Latin America and the Caribbean (and now 16 cases in a small geographic area in Florida), it appears that the risk of spread due to the Olympics is very small. Here are a couple of scientific sources that model this low risk, and I would agree with this approach from Lewnard et al., 2016 and Grills et al., 2016.

Of course some people feel otherwise. To balance this discussion, have a look at this paper recently published as well. You can find that paper here.

The editor's reply to this article is also worth reading here.

Without interference, can you predict how long it would take for Zika to spread globally? As mosquitoes favour warmer climates, are countries with colder climates without risk? Or can the virus spread in a number of ways?

Dr. Bogoch: It would be very challenging to predict how long it will take the virus to spread globally. We know the factors that play into the spread of this virus: warmer temperatures, elevations below 2,000 meters, presence of appropriate mosquitoes, non-immune population, and degree of international travel, to name a few.

You are entirely correct about the countries with different temperatures. Colder places will either have no mosquito-related transmission or the potential for only seasonal transmission during warmer months, depending on the presence or absence of mosquitoes that transmit Zika virus.

Other than bug spray, and staying clear of marshy areas, what else can be done to lessen risk? And what are tell-tale signs you may have it?

Dr. Bogoch: At an individual level, applying bug spray, wearing pants and long-sleeved shirts, and if possible, using permethrin on clothing will be very effective. Remember that the mosquitoes that transmit Zika virus tend to bite during the day and are particularly active at dawn and dusk. The Canadian Public Health Agency has good guidelines on how to prevent mosquito bites here.

It is also important to remember that there are many infections that can be transmitted by mosquitoes in tropical and subtropical zones. For example, malaria, Dengue fever, West Nile Virus, and chikungunya may be present in certain regions. It is always a good idea to avoid mosquito bites, day and night.

Does contracting Zika pose long-term increased risk of pregnancy complications, or do risks return to normal after the infection subsides? If risks return to normal, how long does it take for this to happen?

Dr. Bogoch: Excellent question and certainly on the minds of many people. I am cutting and pasting this paragraph from the CDC (USA) webpage as they say it best:

"Based on the available evidence, we think that Zika virus infection in a woman who is not pregnant would not pose a risk for birth defects in future pregnancies after the virus has cleared from her blood. From what we know about similar infections, once a person has been infected with Zika virus, he or she is likely to be protected from a future Zika infection."

Just to add to this, the virus is cleared from a person's blood in a few days (typically less than seven).

We should consider both the female and male partners when discussing risks of Zika virus infection and pregnancy. I have discussed the prevention of sexual transmission in another response on the AMA, but here is a good link to the CDC's sexual transmission recommendations here.

Please note that there are some subtle differences in guidelines between countries.

What is the incubation period of the Zika virus if at all? Does the Zika virus present immediate symptoms?

Dr. Bogoch: The incubation period for Zika virus is quite short…less than two weeks, but typically in the three to six day range so symptoms, although mostly mild, can occur after that period. In the vast majority of individuals who get symptoms from their infection, this should be quite mild and resolve in two to four days.

How does the virus affect transplant patients? Are children at risk? Can the virus be transmitted through breast milk? For answers to these questions and many others, read Dr. Bogoch's full Reddit 'Ask Me Anything'  here.