Pregnant women should be advised not travel to areas with ongoing Zika virus outbreaks, the World Health Organization says. 

The precautionary advice came out of the WHO's emergency committee for the Zika virus on Tuesday.

Experts have been reviewing scientific evidence to guide public health recommendations since WHO declared a public health emergency last month, saying the virus's association is "guilty until proven innocent" for the birth defect microcephaly and Guillain-Barré syndrome, a rare disorder of muscle weakness and sometimes paralysis.  

The United Nations public health authority held a news conference Tuesday to provide an update on the link between the Zika outbreak in 31 countries in Latin America and the Caribbean and neurological conditions, travel recommendations, trade and advice for pregnant women.

Dr. Margaret Chan, WHO's director general, said the committee's experts pointed to evidence of the virus in amniotic fluid and crossing the placental barrier, as well as other abnormalities during pregnancy. "Grave outcomes" also include fetal death and injury to the central nervous system. 

"Clearly Zika infection during pregnancy will produce very bad outcomes," Chan told reporters. "It is important we recommend strong public health measures and not wait until we have definitive proof."

Microcephaly in French Polynesia, Brazil

So far, microcephaly associated with Zika infection has only been observed in French Polynesia and Brazil. Intense surveillance for fetal abnormalities is underway in countries such as Colombia, where Zika virus outbreaks started later than in Brazil. 

In a statement released ahead of the news conference, WHO said, "Pregnant women should be advised not to travel to areas of ongoing Zika virus outbreaks; pregnant women whose sexual partners live in or travel to areas with Zika virus outbreaks should ensure safe sexual practices or abstain from sex for the duration of their pregnancy." 

Asked why WHO didn't advise women in affected countries not to get pregnant, Chan said it makes sense to provide them the means, such as contraception, subject to national implementation and laws.

Previously, WHO advised pregnant women to discuss their travel plans with their health-care provider and consider delaying travel to any area where locally acquired Zika infection is occurring. 

Dr. David Heymann, chairman of the emergency committee, noted the travel advice is for areas of ongoing transmission not countries.

Countries are responsible for deciding where there are ongoing outbreaks, and people travelling must make their decisions based on that information, Heymann said. 

Chan said nine countries have reported increasing cases of Guillain-Barré syndrome or lab confirmed Zika among GBS cases in people of all ages.

In areas with known Zika virus transmission, health services should be prepared for potential increases in neurological syndromes that could need intensive care, as well as congenital malformations, Chan said. 

The committee also called for "intensified" research into the relationship between new clusters of babies born with
abnormally small heads and other neurological disorders to determine if there's a casual relationship.

Precautions against mosquito bites

Currently, WHO advises all travellers, including pregnant women, going to areas with locally acquired Zika infections to follow standard precautions to avoid mosquito bites:

  • Use insect repellent.
  • Cover up with clothing.
  • Use screen barriers and bed nets to fend off the day-biting mosquitoes.
  • Eliminate potential mosquito breeding sites. 

Until more is known about the risk of sexual transmission, WHO also advises all men and women returning from an area where Zika is circulating — especially pregnant women and their partners — to practice safe sex, including through the correct and consistent use of condoms.

"Reports and investigations from several countries strongly suggest that sexual transmission of the virus is more common than previously assumed," Chan said. 

20 Canadians test positive for Zika

Canada's chief public health officer, Dr. Gregory Taylor, told a Commons committee on Monday that 20 Canadians, including a pregnant woman, have tested positive for the Zika virus. The infections all occurred while visiting countries with outbreaks.

There are no known instances of Canadians being infected while in Canada.

Canadian authorities advise women wishing to become pregnant to wait two to three months after their return from an affected area before trying to conceive. The precautionary measure is based on current information on the incubation period and uncertainty about how long the virus remains present in body.

Similarly, anyone who has travelled to a country with Zika must wait 21 days after returning to Canada before donating blood.

With files from Reuters and The Associated Press