While emphasizing that the Zika virus presents a “very low” risk to Canadians, public health officials are asking Canadians who have travelled to affected countries to defer donating blood for one month after they return.

Canada’s Chief Public Health Officer, Dr. Gregory Taylor, told reporters Friday that they are monitoring the Zika virus outbreak affecting 20 countries in South and Central America, as well as the Caribbean.

He said there is still no international consensus on how long potential blood donors should wait after travelling before donating blood, but that research is ongoing.

“In the meantime, Canadian Blood Services is asking all potential donors who have recently travelled to places outside Canada, U.S. and Europe to postpone their appointments for one month following their return,” Taylor said.

Dr. Theresa Tam, the deputy Chief Public Health Officer of Canada, said the one-month deferral period was chosen because it’s believed that humans clear their bodies of the virus fairly quickly after infection.

Only about 20 to 25 per cent of those infected with Zika develop symptoms, which can include a rash and fever. Those symptoms typically last a week or less, and the vast majority of those infected recover with no complications.

In his remarks to reporters, Taylor emphasized that the risk to Canadians from Zika is low.

“The mosquitoes known to transmit the virus are not established in Canada and are not well suited to our climate. For this reason, the risk to Canadians of Zika virus infection is considered very low,” he told reporters

“Although it is possible that persons travelling abroad may contract the virus, the Zika virus does not present a significant public health risk to Canadians.”

But he reiterated PHAC’s advice that pregnant women and those considering becoming pregnant should discuss their travel plans with their health care provider and consider postponing travel to areas where the Zika virus is circulating.

Taylor noted that the link between Zika virus and microcephaly (the birth defect in which babies are born with unusually small heads) has still not been proven, but that he and his team will be monitoring research developments.

Meanwhile, a Zika infection has been confirmed in another Canadian traveller.

Quebec public health officials confirmed Friday that a woman who had travelled to the Caribbean for a holiday was infected while on her trip. She has since fully recovered and has returned to work.

On Thursday, BC Centre for Disease Control officials confirmed that two B.C. travellers had also been infected while travelling; one had been to El Salvador and the other to Colombia.

An Alberta traveller who returned from an unidentified country was also infected.

In a conference call with journalists Thursday, officials with the World Health Organization’s epidemic response team in the Americas said there could be as many as 3 to 4 million cases of Zika infection in North, South and Central America over the next year.

He said that estimate was based on the previous spread of dengue fever, which is also carried by the same mosquito species.

But Aldighieri noted that the vast majority of those cases will be asymptomatic. This "silent circulation" of the disease will make tracking the virus’ spread more difficult, he said.