There is rising concern about the number of measles cases showing up in Canada, and now there's a new public health advisory.

It’s directed at people planning to travel outside of Canada.

Ontario’s chief medical officer of health Arlene King is warning people to be careful when travelling outside Canada especially to Thailand, the Philippines, or Europe, where the virus has been circulating. King says measles anywhere is a threat everywhere.

Measles is a highly contagious disease that can have serious side effects including diarrhea, fever, pneumonia, infections of the brain and even death. Symptoms begin to appear after seven to 18 days after a person has been infected.

Victoria Pieri is a mother with a young son. And like many parents she is just catching word about 11 confirmed cases of measles in the province, including one in York Region.

“It makes me nervous. I am already worried about so much. The flu and stuff like that. It worries me,” she says.

The highly contagious disease is also in British Columbia with more than 300 cases reported there.

So far, all of the cases were picked up by people travelling outside the country. There hasn't been a case of measles that originated in Canada since 1998. There haven't been any confirmed cases in Simcoe County or Muskoka since 2008.

“It spreads very easily it hangs in the air so it's very communicable, it's probably the most communicable of all the viruses so shares well,” Ann Corner with the Simcoe Muskoka District Health Unit.

Corner had measles as a young child herself. She says now children are given two vaccinations to fight the virus.

“On or after the first birthday and then again for school entry between four and six years and that second shot seems to do the trick seems to really boost the immunity and offer great protection,” she says.

Measles vaccinations started in 1963. If you were born before1970, you probably either had the disease or were exposed to it. People born after that have likely been vaccinated.   

While measles haven't so far shown up in Simcoe Muskoka, they could. And public health experts say if anybody thinks they might have the disease they shouldn’t go to the hospital or a doctor's office or walk-in clinic without calling first.

Measles are so contagious that precautions have to be taken to prevent them from spreading.