It is hailed as the world's biggest sporting event, with hundreds of thousands of people making the pilgrimage every four years so they can sit in close company, sing songs, rattle their caxirolas and cheer for their country's finest soccer players.

Such is the essence of the FIFA World Cup. It is as much a celebration of sport as it is a reason to party.

But for the tournament in Brazil that starts in June, a hazard lies in wait, and it has to do with all those visitors and what they could be bringing with them – the infectious measles virus.

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As the airborne disease continues its global tour, Brazilian organizers and international health officials have been preparing for the worst. They know the conditions are ripe for an outbreak of disastrous proportions.

Here is why: Until recently, Brazil had one of the strongest immunization rates on the planet. It went years without recording a single case of measles. In 2012, it had two. But last year, the Brazilian ministry of health noted 201 cases. Through January and February of this year, the count was 74 and continues to go up.

Added to that is the spread of the disease from the Philippines and the Netherlands to Canada, the United States and other nations. Of the 32 countries competing in this World Cup, 26 have reported having measles. Toss in an expected 600,000 visitors headed to the tournament's 12 cities and what you have is a stick of dynamite in search of a spark.

"If Brazil has a good enough immunization system and high enough coverage to prevent a spread of measles then even if cases are imported it should not cause major outbreaks," said Natasha Crowcroft, Public Health Ontario's chief of infectious diseases. "But it's a real test of whether they have a good system."

Dr. Crowcroft is part of a working group trying to keep measles from contaminating Brazil and its neighbouring countries. She is a member of the International Expert Committee that has been busy for several years getting Brazil ready for the incoming crowds, not just for the World Cup but for the 2016 Summer Olympics to be held in Rio de Janeiro.

The IEC has met with Brazilian officials and the Pan American Health Organization. Watching the proceedings is the Washington regional office of the World Health Organization. Fresh on everyone's mind is the 2012 European Cup.

That tournament was hosted by Poland and the Ukraine while more than 10,000 people in the Ukraine were suffering from measles. WHO Europe issued warning after warning. No one wanted visitors catching the virus and then taking it home with them. That didn't happen, although health officials can't explain why. In an online survey, fans were asked if they had followed the health travel advice and gotten immunized – 77 per cent said they were unaware of the multiple warnings and had missed them completely.

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In Brazil, the fear is outsiders coming in with the virus and leaving it behind. Officials with the country's Ministry of Health outlined to The Globe and Mail the many precautions they have taken:

Since 2011, the ministry has reinforced its prevention of transmittable diseases in all 12 cities hosting World Cup matches. It has vaccinated people who will be working in close contact with tourists. All the vaccinations are free and children have cards to document what shots they have received and when.

It also launched an information campaign using soccer lingo: "Block measles and rubella!" and "Vaccination: Your best shot."

"[We will be] increasing awareness of vaccination among travellers at least two weeks prior to their departure," said Pamela Bravo, a specialist in family immunization for PAHO. "[We] will be displaying health alerts warning travellers of measles and rubella symptoms and instructing people to stay at home or in their hotel and call a doctor."

But those bound for Brazil will not be asked to produce proof of having been vaccinated – nor will there be any checks to determine if people are sick when they arrive. The hope is that tourists and their children come in healthy and stay that way for the duration of the World Cup.

It is a wish shared by other countries.

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"One of the questions I am asked is how global work is relevant to Ontario," Dr. Crowcroft said. "These recurrent importations into Canada are telling us that we need to help the rest of the world to eliminate measles if we're going to stop it for good. … With the level of diversity and connectedness to the rest of the world, infectious diseases recognize no borders."

That concern extends to next year, when Toronto and other Southern Ontario cities host the Pan American and ParaPan American Games. Once again, there will be people in close proximity to one another. Health-care workers are quick to point out that no athletes from Europe or the Philippines, where measles outbreaks have been particularly heavy, will be competing in Canada. And the crowds, compared to what the World Cup draws, will be smaller and more manageable.

As for Brazil, officials believe they have done their best and stand in readiness for the worst.

With a report from Manuela Andreoni in Rio de Janeiro