Dr. Andrea Boggild
Dr. Andrea Boggild, the study’s lead author and Clinical Director, Tropical Disease Unit, Toronto General Hospital, says the perception Zika is associated with a more mild or benign clinical course than that of dengue or chikungunya was not borne out in the small cohort. (Photo: Courtesy Andrea Boggild)

A one-year study of Canadian travellers with Zika infection suggests that complications from the Zika virus may be underestimated, with higher rates than among those with other viral diseases spread by infected mosquitoes.

Examining 1,118 returned Canadian travellers who travelled in the Americas and who sought care in a "Canadian Travel Medicine Network" site from Oct. 1, 2015 to Sept. 30, 2016, the researchers found that 41, or 3.7 per cent, of them were infected with the Zika virus, the same number had dengue and 23, or 2.1 per cent, had chikungunya.

However, four people, or 10 per cent of the 41 travellers with Zika, had a severe complication, as compared with none of the dengue or chikungunya-infected travellers.

Dengue is one of the most common causes of fever in returning travellers, and a common cause of hospital admission among returning travellers in general.

Severe complications of Zika virus included symptoms similar to those of Guillain-Barré syndrome – such as numbness and paralysis - and meningitis.

Perception not borne out by study

The study entitled, "Surveillance report of Zika virus among Canadian travellers returning from the Americas," is published in today's edition of the CMAJ (Canadian Medical Association Journal).

"The perception that Zika is associated with a more mild or benign clinical course than that of dengue or chikungunya was not borne out in this small cohort," said Dr. Andrea Boggild, the lead author, Clinical Director, Tropical Disease Unit, Toronto General Hospital, member of U of T's Department of Medicine, and Parasitology Lead, Public Health Ontario Laboratories.

Almost all the travellers with Zika virus acquired it through mosquito bites, and one through sexual transmission. Most of the Zika cases occurred in Canadians who were travelling as tourists or were visiting friends and relatives in the Caribbean and Central America. 

There is no vaccine for the prevention of Zika. The researchers caution that in the case of current or planned pregnancy, travel should be deferred.  Travellers should protect themselves by covering up with long-sleeves and long pants, use repellant that contains DEET (20 per cent to 30 per cent), bed netting treated with insecticide, and condoms to minimize the risk of sexual transmission.

What is Zika?

Zika, dengue and chikungunya are viral diseases, transmitted by mosquitoes, causing sudden fever, rash, and acute pains in the joints.

Zika virus infection can also be transmitted from an infected pregnant woman to her developing fetus. In addition, Zika virus can be sexually transmitted, and the virus can persist for an extended period of time in the semen of infected males.  In 2015, Brazil reported an association between Zika virus infection and Guillain-Barré syndrome, a neurological disorder that could lead to paralysis and death, and microcephaly, children born with unusually small heads.

Zika virus continues to spread geographically to areas where mosquitoes are present that can transmit the virus. The Public Health Agency of Canada recommends that pregnant women and those planning a pregnancy avoid travel to countries or areas in the United States with reported mosquito-borne Zika virus. 

Information for travellers can be found on Government of Canada website, Zika virus: Advice for travellers and Committee to Advise on Tropical Medicine and Travel (CATMAT).​

The Canadian Travel Medicine Network is an initiative of the Centers for Disease Control and Prevention and the International Society of Travel Medicine (ISTM), in collaboration with the Public Health Ag​ency of Canada (PHAC).  The core sites are members of the GeoSentinel Global Surveillance Network, a worldwide communication and data collection network for the surveillance of travel related morbidity. 

An interview with Dr. Boggild can be found in a podcast here.

A visual abstract to the study can be found here.

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