8 things you need to know about the Zika virus

Update January 25, 2016: The World Health Organization (WHO) says the Zika virus is likely to spread to all of the Americas, except for Chile and Canada, where the species of mosquito known to transmit the virus isn't found. Researchers are now investigating whether the virus can be transmitted sexually (the WHO says there is "one case of possible person-to-person sexual transmission," and currently no evidence of Zika being transmitted to babies through breastmilk). While work on a vaccine is ongoing, women in affected areas, including Brazil, Colombia, Ecuador, El Salvador and Jamaica, have been advised to delay pregnancies until more is known about the virus.

A mosquito-borne virus is spreading in holiday hotspots like Mexico, South America and the Caribbean, and it’s of particular concern to pregnant women. The Zika virus, first identified in Brazil in May, may be linked to severe birth defects. In particular, there seems to be a correlation with a condition called microcephaly, where babies are born with smaller-than-average heads and underdeveloped brains, which, in some cases, can be fatal. Research into Zika is new and still emerging, but troubling nonetheless: the BBC reports there have been around 3,500 reported cases of microcephaly in Brazil alone since October, a 30-fold increase.

The Public Health Agency of Canada (PHAC) and the US-based Centers for Disease Control and Prevention (CDC) has issued a travel alert for countries where Zika virus transmission is ongoing: Brazil, Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Suriname, Venezuela, and the Commonwealth of Puerto Rico. The CDC has also recently added the United States Virgin Islands, Dominican Republic, Barbados, Bolivia, Ecuador, Guadeloupe, Saint Martin, Guyana, Cape Verde and Samoa to the Zika virus list.

Both the PHAC and CDC recommend that pregnant women and women trying to become pregnant should consider postponing travel to the areas where Zika virus transmission is ongoing. If travel cannot be postponed, expectant women to should talk to their doctor or other healthcare provider and strictly follow steps to avoid mosquito bites during the trip. What's more, the CDC advises pregnant women who have travelled to affected areas be tested for the virus if they show two or more symptoms (fever, rash, joint pain or pink eye/eye irritation) during or within two weeks of travel.

We spoke to Isaac Bogoch, a tropical infectious disease specialist at Toronto General Hospital, to ask your questions about the Zika virus.

Is there a definite link between the Zika virus and microcephaly? Isaac Bogoch: As of today, January 15, 2016, we do not have a definite causal link between the two. However, there are several arrows pointing to a strong association and this is clearly a major focus of research.

Are there other birth defects, besides microcephaly, considered to be linked to the Zika virus? IB: You have to remember this is all very new. We are in very early phases and we just don’t have enough information right now. It looks like microcephaly is the predominant birth defect. There might be more.

What’s the actual risk of infection if you’ve vacationed in one of the countries where it is present? IB: The exact extent of the infection is not entirely known. There were several cases in Brazil in the middle to late part of 2015. Over the last few months the number of cases in Brazil has grown, and we’ve seen cases pop up in 13 other countries, ranging from Brazil all the way north to Mexico. So it’s in South America, Central America, Mexico and some Caribbean countries.

One of the major challenges with this virus is that about 80 percent of people who get infected will have no symptoms or very mild symptoms. People can be infected and not even know it. It’s hard to know the extent of the virus, so we don’t know the likelihood that the mosquito that bit you is carrying the virus.

What are the symptoms? IB: For those who do have symptoms, they are typically mild: fever, muscle and joint pain, maybe a rash and some people get conjunctivitis (irritation of the eyes). This lasts for two to three days and then they improve and recover. It’s not something that would be severe enough for most people to even see a doctor. But when we talk about who is symptomatic—that’s just the tip of the iceberg. There are probably a lot more people with the virus than we think.

Is there a test for pregnant women who have recently travelled to one of these countries? IB: A blood test can be done right now in Canada, but would need to be sent to a public health reference laboratory for analysis—the wait time for results varies from province to province. If you do have it, there’s unfortunately not much you can do: there’s no vaccine or treatment for the infection, but this is a very active area of research right now.

(Editor’s note: In its latest statement, the CDC says that expectant women who test positive for the Zika virus should be monitored with regular ultrasounds and referred to a specialist to monitor the development and anatomy of the fetus).

Has the virus been identified in the US? Should people worry about travelling to Florida for their vacation? IB: There have been travellers who have gone to Zika-virus endemic areas and have come back to the US with the infection, but it has not been locally acquired in the US. The virus cannot be transmitted from person to person—you need to be bit by an infected mosquito. Florida has the right climate and the right mosquitos to transmit this infection, but as of today, there’s no Zika virus in Florida.

Will the virus come to Canada? IB: Travellers who go to a Zika-virus affected area can get infected and be sick in Canada, but we don’t have the right mosquitos to transmit the virus, so you cannot acquire the infection in Canada.

(Editor's note: The PHAC reports that travel-related cases of Zika virus have been reported in Canada in travellers who have returned from affected countries.  There have been no reported cases of locally acquired Zika virus in Canada.)