TORONTO – The agency responsible for most of Canada’s blood supply will soon turn away donors who have travelled to countries where the mosquito-borne Zika virus is rampant.
More than 20 countries in South and Central America and the Caribbean, as well as parts of Mexico, have reported widespread cases of Zika virus infection, which is transmitted by the day-biting Aedes mosquito. That mosquito is present throughout the Western Hemisphere, except in Canada and continental Chile.
Following discussions with Health Canada and its counterpart Hema Quebec, Canadian Blood Services will decide in the next few days which travel destinations are considered a high enough risk that visitors to those countries would be temporarily stopped from donating blood, and for how long.
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“We think that the chance of Zika virus showing up in the Canadian blood supply is very remote, but we don’t want to sit here and do nothing, knowing that Zika virus is spreading around in areas where Canadians are potentially going to be travelling,” said chief medical and scientific officer Dr. Dana Devine on Thursday from Ottawa.
Canadian Blood Services also realizes there will likely be a shortfall in the amount of blood donated.
“We anticipate a reduction in the number of donors due to this ineligibility period and encourage Canadians to donate before they travel to help make up for the anticipated shortfall,” the agency said in a statement on its web site.
So far, three cases of Zika infection have turned up among Canadians travellers, two from B.C and one from Alberta; two had been visiting El Salvador and one was in Colombia. All three have since recovered.
Most people with Zika never know they’ve been infected because they experience no symptoms. Those who do develop symptoms – fever, malaise, skin rash, joint pain and red eyes – typically get better after a short-lived illness.
But the most pressing worry is for pregnant women and those who plan to become pregnant. Since Zika became endemic in Brazil last year, about 4,000 infants have been born with small heads and underdeveloped brains, a condition known as microcephaly.
While Zika hasn’t been proven to cause the birth defect, the Public Health Agency of Canada is advising pregnant women and those who plan to become pregnant to consider postponing travel to areas where Zika has taken root.
The reason women who are thinking about getting pregnant need to take precautions is because scientists don’t know if Zika remains in the body after blood tests indicate the active virus has disappeared.
“It’s a critically important question, and the reality is we don’t really know at this point in time,” said Dr. Andrew Simor, an infectious disease specialist at Sunnybrook Health Sciences Centre in Toronto.
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“There are some potential concerns that it may persist in certain protected sites, the same way that we discovered Ebola virus does,” Simor said. There have been at least one or two cases of what appears to be sexual transmission of the virus, suggesting Zika may remain dormant in semen, as it can with Ebola.
“But I want to emphasize that it’s not well-documented and the information that we have is really very limited,” Simor said.
As for Zika being a potential cause of microcephaly in newborns, he said there’s a theory that the virus is able to cross the placenta, based on one study that detected evidence of Zika in the placental tissues of babies born with the birth defect.
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“So that would lend to some biologic plausibility that it’s Zika virus responsible for the microcephaly,” said Simor, adding that women who are pregnant or plan to get pregnant should think twice about travelling to areas rife with cases of infection, unless they have no choice.
“I think if it’s just going for a vacation, I would encourage them to look for a different vacation spot.”
The planned deferral of donations from travellers to disease hotspots isn’t a first for Canadian Blood Services.
The agency already temporarily prohibits donations from travellers who have returned from countries where malaria, which is also spread by mosquitoes, is endemic.
“If you have travelled to a place that has malaria, we would currently be deferring you for 12 months,” Devine said. “If you’ve been in a Zika-risk area, you’re going to be deferred and it will be a much shorter period of time because it doesn’t hang around like malaria does.
“It would be weeks, not months,” she suggested. “But we haven’t quite decided yet what exactly the length of time will be.”
Devine said there could also be some overlap: certain countries or regions where malaria-carrying mosquitoes are present may now also be home to the Zika virus, which originated in Africa and spread to southeast Asia, then made its way to the Pacific Islands, and last year to the Western Hemisphere.
It’s not clear how easily Zika virus could be transmitted through a blood transfusion, although two other viruses spread by the Aedes mosquito – dengue and chikungunya -“are highly likely to be transfusion transmissible,” she said.
“So we’re making these plans based on the assumption that there is a risk, without the clear evidence that that risk is present.