Canada Zika study: Disease More Serious Than Thought

TORONTO – Hundreds of Canadians have contracted the Zika virus, almost all of them abroad. But little is known about their situation. To fill this “gap”, researchers scanned information about patients who bumped into a Canadian network of seven clinics specializing in tropical medicine called CanTravNet.


These people consulted a doctor after getting sick as a result of a trip. Surprise: the proportion of them who were infected with the Zika virus was higher than expected, and their symptoms were significantly more severe than might have been expected. “Our sample is small, which may explain some unexpected signals. But there are several surprising elements in this report, “commented to La Presse Cedric Yansouni, deputy director of JD MacLean Centre for Tropical Diseases at McGill University and one of the authors of the study published today in the Journal of the Canadian Medical Association .

One of the big surprises is the frequency of Zika fever cases. Of 1118 patients attending specialist clinics between October 2015 and September 2016, 41 had Zika fever. This is as much as for dengue, and more than for the Chikungunya (23 cases).

“Dengue and Chikungunya are very common diseases among Canadian travelers returning from tropical countries. So Zika fever seems far from being a rare disease, “says Yansouni.

Three pregnant women were among the affected patients, two of whom transmitted the virus to their fetus. Remember that the Zika virus can cause serious malformations in fetuses, especially microcephaly (babies with too small head).

Researchers estimate that their sample accounts for about 15% of Zika cases diagnosed in Canada.

Severe symptoms

The other amazing aspect is the severity of the symptoms of patients. “Zika fever is often described as dengue fever without complications. In our cohort, severe symptoms and neurological complications were found to be much higher than with dengue, “says Cedric Yansouni.

No fewer than 88% of patients suffered from rash, 80% fever, and half reported muscle and joint pain or headaches. Two travelers suffered from Guillain-Barré syndrome, a serious illness. Add to that the two infected fetuses, and you have, in only 41 cases, the whole spectrum of problems that have already been associated with the Zika virus.

It should be noted that the sample of researchers is not representative of all cases of Zika. Approximately 80% of people infected with the virus have no symptoms and therefore will not seek medical attention in specialized clinics. Still, scientists did not expect to see such a complication rate in symptomatic patients.

“Our findings suggest that complications resulting from Zika infection are underestimated by data coming exclusively from populations where Zika is endemic,” write Canadian researchers.

Risk of actual transmission

The vast majority of Canadian travelers infected abroad were infected by a mosquito bite. But one of the patients in the sample was infected by sexual transmission, in addition to the two fetuses that contracted the virus from their mother.

According to the researchers, observing such cases in a sample of only 41 people shows that there is a “strong potential” to catch the Zika by secondary transmission in Canada. Remember that the species of mosquitoes that transmit the virus do not live under our latitudes, hence the impossibility of contracting it by a sting.

Warnings maintained

According to expert Cédric Yansouni, the surveillance report unveiled today does not justify modifying the public health warnings already conveyed by the Canadian authorities. “The data in our report supports the current recommendations,” he said.

The Public Health Agency of Canada (PHAC) recommends that pregnant women and prospective mothers avoid travel to affected areas (including parts of Florida, in addition to a large proportion Of Latin America). Men returning from such areas should have protected sex for six months to avoid infecting their partners. All travelers should protect themselves from mosquito bites by covering and using insect repellents.

CanTravNet Network

The CanTravNet network has seven travel medicine and tropical medicine clinics, two of which are in Quebec (associated with McGill University and Saint-Luc Hospital). Its mission is to oversee the diseases contracted by Canadians abroad. It is part of an international monitoring network called Geosentinel.


Main countries / regions where infections occurred in 41 patients

Colombia (7 cases)

Trinidad and Tobago (6 cases)

Nicaragua (5 cases)

Barbados (3 cases)

Salvador (3 cases)

Martinique (3 cases)