Chikungunya Outbreak in the Americas: Impact on Imported Chikungunya Cases among Canadian Travellers

Posted: September 18, 2015

In 2014, a total of 429 confirmed cases of imported chikungunya disease were documented among returning Canadian travellers.  As of 1 July 2015, an additional 91 confirmed and over 100 probable imported cases have been detected.

Confirmed cases were documented based on reactivity by a CDC based in-house IgM ELISA and positive viral neutralization titres and/or the presence of viral RNA in clinical samples. Patients whose specimens test positive for anti-chikungunya IgM only by ELISA are designated as probable cases.

Approximately 4000 suspect case samples were submitted to the National Microbiology Laboratory for testing in 2014 and 2015. This is a sharp increase compared with past years, in which total submissions averaged 200 samples per year. From 2008 to 2013, an average number of 10-15 imported cases per year were identified among Canadians. Hence 429 cases represents a highly significant increase in yearly totals for Canadians infected by the virus and not surprisingly corresponds to the ongoing outbreak in the Americas. All Canadian
provinces have documented at least one imported case of chikungunya with most of the cases involving travellers from the provinces of Ontario (57 per cent) and Quebec (30 per cent).

Although travel histories were only available for 1/3rd of the patients identified in 2014, the vast majority of individuals (93 percent) with documented travel information did travel to the Americas, particularly the Caribbean. Countries in the Americas in which Canadian travellers were presumably exposed to the virus include: Aruba, Barbados, Colombia, Dominica, Dominican Republic, El Salvador, Grenada, Guyana, Haiti, Jamaica, Martinique, Puerto Rico, St Lucia, St Martin, Trinidad and Venezuela. Caribbean countries also made up the majority of the travel histories for cases identified early in 2015 (January to March). However, during the past several months, an increasing portion of cases have involved travel to Central and South
America and included countries not listed above, such as Panama, Nicaragua, Ecuador, and Brazil. Most of the cases involving travel outside the Americas were identified among Canadians who had visited countries in Asia (5 per cent); however, imported cases involving
Africa and the Pacific-Oceania regions were also documented.

Currently, the proportion of laboratory-identified cases among patients clinically suspected of chikungunya disease has dropped from almost 20 per cent in late 2014 and early 2015 to less than 10 percent in the past several months (March-June 2015). These data reflect trends currently observed in the Caribbean where outbreak activity has decreased. However, imported cases continue to be recognized among Canadians travelling to endemic areas where the virus is circulating, and preventative measures should still be emphasized to avoid exposure.

Of interest, 26 per cent (112/429) of the cases identified in 2014 were found to be viremic using PCR-based diagnostic procedures. At this time, the probability of local transmission is very low due to the absence in Canada of the primary mosquito vectors that transmit the virus (Aedes aegypti and Aedes albopictus). However, the expansion of  A. albopictus_to southern regions of Canada is a possibility in the future if factors such as climate change contribute to its northward spread.

Contributed by Dr. Mike Drebot