Canadian adults who went to travel medicine clinics sick with the Zika infection show a range of symptoms, including severe complications, a new study suggests.
The Zika virus is spread by mosquitoes in the Caribbean, South America, Central America and some U.S. states.
A common perception is that Zika is associated with mild, flu-like symptoms and rash.
But that was not borne out among the 1,118 travellers who visited travel medicine clinics at cities in British Columbia through Quebec from October 2015 to September 2016.
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"We were a little bit surprised that we noted five per cent of cases had a neurologic complication," said Dr. Andrea Boggild, clinical director of the tropical disease unit at Toronto's University Health Network. "Then five per cent had congenital transmission."
Most people with Zika won't have symptoms. But until now, surveillance data on Zika virus in returning Canadian travellers hadn't been analyzed.
The study in Monday's issue of the Canadian Medical Association Journal showed Zika was diagnosed as often as dengue.
A threat of paralysis
The researchers only looked at people sick enough to see a health-care professional and be referred to a travel health clinic — a small subset that's likely biased toward more complicated cases, Boggild cautioned.
The study's authors found that overall in the group, 41 travellers had Zika and 41 had dengue. The doctors didn't find any severe complications in the dengue group.
In contrast, severe complications of Zika included Guillain Barre, a neurological syndrome that can lead to paralysis that is often temporary, as well as meningitis, and congenital transmission or birth defects.
Dr. Shaun Morris, a principal investigator at SickKids Centre for Global Child Health in Toronto, was not involved in this study, but he said it offers important findings about adult Canadian travellers.
"Zika potentially can cause meaningfully significant disease in the non-pregnant women population as well," Morris said. He is part of a surveillance program launching across Canada to identify and track children born with congenital Zika syndrome.
Pregnant? Delay travel
A main concern was that in pregnant women, Zika infection can cause microcephaly, a malformation where babies are born with abnormally small heads and a poorly developed fetal brain because neurons die and fail to form properly.
"One major message for the pregnant traveller is that we are continuing to advise deferral of travel to areas where Zika virus is transmitted because of the devastating consequences to the fetus," Boggild said.
Almost 60 per cent, 24 travellers, with Zika were women. Of these, 79 per cent or 19 were of child-bearing age.
In the milder cases, nearly 90 per cent had rash and 80 per cent had fever.
The Zika cases from travel health clinics account for about 12 per cent of those across Canada.
The Society of Obstetricians and Gynaecologists of Canada said it wants to know more about Zika beyond the urban centres included the study.
"The findings show that we really need to get a better understanding in Canada about Zika, its complications and its transmission," said Jocelynn Cook, the society's chief scientific officer in Ottawa. "One way to do that is to really work together with the provinces, the territories, the researchers and the clinicians and the Public Health Agency of Canada to develop a system where we can do some reporting, some monitoring and some surveillance."
By better understanding what happens in the womb when a woman is infected with Zika, researchers hope to eventually find ways to potentially intervene, Cook said.
Dr. Isaac Bogoch, a tropical infectious diseases expert at Toronto General Hospital who was not involved in the research, also sees the value of stepping up monitoring for Zika cases among Canadian travellers.
"It would be very helpful if there was a strategy in place that we would know where all the cases were so we could follow up with any individual that has a positive test," Bogoch said.
Boggild and Bogoch said the findings should remind travellers to take precautions against illnesses spread by mosquitoes, not only Zika but also dengue, chikungunya and malaria:
- Use a repellent containing DEET or Picaridin on the skin and clothing.
- Use barrier precautions against sexual transmission while travelling and upon return.
- If sick after return from the tropics, seek medical assessment to rule out life-threatening infections such as malaria.
"It's always a good idea before travelling to the tropics to speak with a travel medicine specialist, just so you have a better understanding of what the risks are and what the possible infections are and ways to mitigate those risks," Bogoch suggested.
'I like to live in ignorant bliss'
At Toronto Pearson International Airport last week, Zika was not top of mind for two travellers heading south for fun in the sun.
"I like to live in ignorant bliss sometimes," Donna Allen said of Zika as she prepared to catch a flight to a resort in Cancun, Mexico. She packed mosquito repellent.
So did Anita Husain, who was headed to Jamaica with her young daughter. Safety was her main concern.
The Public Health Agency of Canada, which funds the travel health surveillance, says that as of Feb. 9, there are 473 travel-related cases and three sexually transmitted cases, including 27 pregnant women reported in Canada.
"This number is expected given that more than five million Canadians travel to Zika-affected countries, and another four million to Florida alone, every year," a spokesperson for the Public Health Agency of Canada said in an email. "The agency is also aware of two pregnancy outcomes with Zika-related anomalies observed, and two with no Zika-related anomalies observed."