A disturbing spike in the number of babies born in Brazil with severe birth defects is focusing attention on an old but little understood virus, called Zika.

On Friday, the U.S. Centers for Disease Control and Prevention warned that pregnant women should consider postponing trips to 14 countries with outbreaks of the virus.

Here’s what you need to know.

What is Zika virus and where did it come from?

Zika is a virus that is transmitted by daytime tropical mosquitos. It’s not new, as it was first documented in parts of Africa and Asia in the 1950s.

But the virus has recently begun to spread, finding its way into the Americas for the first time.

How dangerous is it?

As viruses go, Zika has always thought to be relatively harmless. The vast majority of those infected never show symptoms. In those who do, the virus typically causes a mild illness (called Zika), marked by a mild fever, rash, muscle pain and red eyes.

The illness lasts only a few days and is rarely serious.

What about the birth defects?

In the last year, doctors in Brazil have been noticing a still-unproven link between Zika and a sudden 20 per cent spike in babies being born there with underdeveloped heads -- a condition called microcephaly.

The worry is that the virus is causing these birth defects in mothers who don’t realize they’ve been infected.

The problem is that this link is difficult to prove, says Dr. Allison McGeer, the director of infection control at Toronto's Mount Sinai Hospital. She says microcephaly is actually fairly common and can be caused by a range of things, which makes it difficult to determine whether the microcephaly described in Brazil is caused by the virus, or merely associated with it and caused by something else.

What's more, other regions that have experienced Zika outbreaks have not reported increases in microcephaly.

Are Canadians at risk?

While it is not currently possible for Canadians to become infected by mosquitos in Canada, they could become infected while travelling to affected countries.

The Public Health Agency of Canada has not issued any travel warnings related to Zika, but it has advised pregnant women to “discuss their travel plans with their health care provider to assess their risk” of contracting Zika.

These women should also take measures to protect themselves against daytime and nighttime mosquito bites.

Which countries should pregnant women consider avoiding?

The U.S. Centers for Disease Control recommends women in any trimester of pregnancy avoiding travelling to:

  • Brazil
  • Colombia
  • El Salvador
  • French Guiana
  • Guatemala
  • Haiti
  • Honduras
  • Martinique
  • Mexico
  • Panama
  • Paraguay
  • Puerto Rico
  • Suriname
  • Venezuela


As well, women trying to become pregnant should consult their healthcare provider before traveling to these areas and strictly follow steps to prevent mosquito bites during the trip, the CDC advises.

Is there a vaccine for Zika?

There is no vaccine to protect against Zika infection, nor is there any particular way to treat an infection.

What's the best way to avoid infection?

The best method is to avoid getting bitten by infected mosquitos. That means:

  • Wear long-sleeved shirts and long pants
  • Use insect repellents containing DEET, picaridin, oil of lemon eucalyptus (OLE), or IR3535. Always use as directed.
  • Insect repellents containing DEET, picaridin, and IR3535 are safe for pregnant and nursing women and children older than 2 months when used according to the product label. Oil of lemon eucalyptus products should not be used on children under 3 years of age.
  • Use permethrin-treated clothing and gear (such as boots, pants, socks, and tents).
  • Stay and sleep in screened-in or air-conditioned rooms.

Will the virus spread to Canada?

The mosquito that transmits Zika is a tropical mosquito and can’t move further than the southern U.S. McGeer says there is the remote possibility that other mosquito species that move farther north could begin to carry the virus. But it’s difficult to assess how real this possibility is, since Zika has not been well studied.

“There’s a lot we don’t know about this virus and a lot we don’t know about its epidemiology, so nobody can talk with confidence about what will or will not happen,” she told CTV’s Canada AM.

But at the moment, PHAC says “the risk of virus establishment in Canada is low.”

Is this because of global warming?

It’s not clear why Zika has spread to the Americas, but it is one of several mosquito-borne infections, including West Nile, chikungunya, and dengue that have moved into areas where it never used to be found.