The number of Canadians who contracted a mosquito-borne virus that first appeared in the Caribbean just over a year ago has soared into the hundreds, and there are likely many more cases that have gone undiagnosed, according to the Public Health Agency of Canada.

Since the spring of 2014, “there has been a large increase in travel-related chikungunya cases diagnosed in Canada,” PHAC reports. As of Dec. 9, 2014, there were 320 confirmed cases and 159 probable cases diagnosed, the agency said, “by far the largest yearly number of chikungunya cases ever documented in this country.

“In all likelihood, this is an underestimate due to missed diagnoses and undetected cases of mild disease,” the agency added.

Most provinces have at least one confirmed case, with the majority being in Ontario (165) and Quebec (114). Another 100 suspected cases were still being investigated at the end of 2014, the agency said.

“This surge in Canadian infections has been associated with the incursion of chikungunya virus into the Caribbean and the expansion of the virus in the Americas,” the agency said in a report issued Thursday.

“Ongoing outbreaks in the Asia-Pacific region have also contributed to imported cases among Canadian travellers.”

Prior to 2014, between one and 20 cases of chikungunya would typically be confirmed in Canada each year.

The chikungunya virus was, until recently, mostly found across Africa, Asia, India and some Pacific islands. Two non-imported cases were reported in Saint-Martin in Dec. 2013, marking the virus’s first appearance in the western hemisphere. Since then, local transmission of the virus has been detected in more than 40 countries in the Caribbean, Central and South America, Mexico and the United States.

There have not been any cases of locally transmitted chikungunya in Canada, likely due to the fact that the virus’s two main mosquito carriers are not found here.

However, Canadians make about 2.5 million visits to Caribbean countries each year, and also travel in high numbers to chikungunya hotspots in the Asia-Pacific region.

'Significant disability'

Symptoms usually develop within three to seven days after a bite from an infected mosquito, starting with fever and joint pain. Pain in the joints typically starts in the hands and feet.

Patients can also develop headaches, a rash, nausea and fatigue.

Most symptoms disappear within days, while other symptoms can last for weeks or months. Severe complications affecting the eyes, brain and heart can also occur.

Infectious disease specialist Dr. Neil Rau says chikungunya is worrisome because it can cause severe arthritis in normally healthy people.

“I have seen a few cases of chikungunya in perfectly healthy people where the arthritis was so significant that it caused a significant disability for up to 6 months,” Rau told CTV News on Friday.

And although Canada’s mosquito season is relatively short-lived, a traveller could return home with the virus during mosquito season, when it could spread among Canadians, Rau added.

There is no vaccine to protect against contracting the virus, and few treatment options beyond symptom management.

This means travellers should take precautions to protect themselves against exposure to mosquitoes when travelling. Doctors should also be asking about travel history when patients turn up at their offices with symptoms such as fevers and joint pain and inflammation.