Could severe complications from Zika infection be more common than previously thought?

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Researchers studying Zika virus in Canadian travelers returning from Central America, South America and the Caribbean have indicated that severe complications could be more common than previously estimated.

Although there have been prior studies documenting exported cases of Zika, data specific to Canadian travelers, who represent a highly mobile population, have not yet been investigated. The study, published recently in the Canadian Medical Association Journal, therefore examined demographic and travel-related characteristics of Zika infection in this group, with the aim of uncovering risk-factors for both acquisition and clinical outcomes.

The team analyzed data from the Canadian Travel Medicine Network (CanTravNet), a Canada-based network of infectious disease specialists focused on detecting travel-related illness. The researchers utilized data from 1118 individuals who had visited one of the CanTravNet clinics to report a travel-related illness from the Americas, this included both returning Canadian travelers and visitors to Canada.

Of all the cases examined, the researchers confirmed that 41 patients (3.7%) had a Zika infection, 41 patients (3.7%) were infected with dengue and 23 (2.1%) of the travelers had a chikungunya infection. The team then looked closer at those with Zika, discovering that almost 60% of the Zika cases were female and a majority (79%) of these women were of child-bearing age.

In addition, the group observed that there was a higher incidence of severe complications than expected. Of three Zika-infected pregnant women in the cohort there were two cases of congenital infection. Moreover, two travelers presented with Gillian-Barré symptoms, one of which was also suffering viral meningitis. Together, the cases presenting with complications compromised 10% of the total Zika cases, whereas no travelers with dengue or chikungunya reported any severe symptoms.

Author Andrea Boggild, from the University of Toronto (Canada), commented: “The common perception that Zika is associated with a very mild clinical course compared with dengue or chikungunya was not borne out in this small cohort.”

The data was taken over a 1 year period from October 2015 – September 2016, and the group emphasize that the use of this data set does have limitations. For example, cases of Zika reported to CanTravNet are estimated to constitute approximately 12% of cases nationwide and, as this only includes travelers who sought care, the results may not translate to all travelers. In addition, children might be overlooked in the data; Boggild explained: “Due to the structure of CanTravNet, our clinics primarily service an adult population, so pediatric cases are under-represented in the database.”

Despite the small cohort observed in this study, the researchers observed a full clinical spectrum of acute Zika infection and they suggest that complications might be underestimated by current data, which is primarily from endemic populations. “Referral bias to our centers may have contributed to the more severe clinical presentations noted for Zika, though we would have expected the same phenomenon to occur with dengue and chikungunya were this a significant contributing bias,” stated Boggild.

In addition, the team note that Zika infections were as common as dengue in this cohort, with 41 cases of each, highlighting the emergence of the Zika virus.

Source: Boggild AK, Geduld JG, Libman, M et al. Surveillance report of Zika virus among Canadian travellers returning from the Americas, CMAJ, 189, E334­40 (2017); https://www.eurekalert.org/pub_releases/2017-03/cmaj-zvi022817.php

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