Canadian health officials are warning that with more than 250 people in Quebec infected by measles, the outbreak could start spreading to the rest of the country too.

There have been 208 cases of measles reported in Quebec since May 1 and a total of 254 since the beginning of the year. That's a huge number, considering that there are typically only 11 cases a year in all of Canada, says the Public Health Agency of Canada.

This is now the largest measles outbreak in Canada since measles was essentially eradicated from Canada in the mid-1990s.

The U.S. is having one of its worst years yet for measles, as well. Health officials there say 118 cases have been reported so far this year -- the highest number this early in the year since 1996. The U.S. normally sees about 50 cases of measles in a year

Just about all the cases in the U.S. outbreak were sparked by people bringing the illness over from other countries. Europe, especially France, has been hit hard by measles this year, with more than 6,500 cases reported in 33 nations.

The Quebec outbreak is being blamed on unvaccinated travellers who went to France and brought the highly contagious disease back home.

"The first cases were from travellers coming back from France who developed their disease here," Dr. Louise Valiquette of Quebec Public Health told CTV Montreal earlier this week.

Dr. John Spika of the Centre for Immunization and Respiratory Infectious Diseases at the Public Health Agency of Canada, says it's possible more cases will be found in other parts of the country.

"We can continue to expect importation of some cases into Canada. So we have to maintain a high level of vaccinations to prevent spread when importations occur," he told CTV News, adding that he expects the number of cases in Quebec to continue to rise.

"The size of the Quebec outbreak is notable, and we appreciate the outbreak will affect a lot more cases."

Quebec's director of public health, Alain Poirier, is urging all Quebeckers to make sure they have had all their vaccinations for measles, which he says is the safest and best way to combat virus.

Measles is spread by droplets from the nose, mouth and throat of an infected person that are released by coughing or sneezing. The virus can hang in the air for up to two hours and people can inhale them just by walking by.

"Measles is probably the most infectious disease we have," says Spika. "We know that when the virus is introduced, it will find those who are susceptible. And that is what is happening."

For most, the illness causes a cough and a full-body rash. People usually recover after about 10 days, but in some, the illness can become serious.

"In some cases of measles, it will lead to complications, such as pneumonia. And in one case of 1,000, you will see a brain infection," Valiquette says.

Around the world, measles kills nearly 200,000 people each year and is a leading cause of death among children in the developing world.

Measles can be prevented with two doses of the measles-mumps-rubella vaccine. Two doses are recommended for children, with the first given around the time of a child's first birthday, and the second dose given after age 15 months or before the child starts school.

But many haven't had the vaccine, in part because of a bogus study that linked the MMR vaccine to autism. While that study has since been debunked and the doctor behind it discredited, the worries raised by that study eroded public confidence in vaccines, leading to drops in vaccination rates in some areas.

This measles outbreak follows a mumps outbreak in Canada in 2009 and 2010 that mostly affected young adults between the age of 15 and 24.

Many people in that age group would have gotten only one MMR dose, since two doses weren't recommended in Canada until 1996.

Spika says that the majority of measles cases in Quebec have been among students in the 10 to 19 age range. He says it is possible that some of these patients didn't receive both doses of vaccine.

"It is also possible if they are immigrants, they may have not received the vaccine in their country of origin," he said, noting that researchers need to understand why the outbreak has unfolded.