The World Health Organization is warning of a new SARS-like virus that has killed 27 people.
The virus, called MERS-CoV, has mainly affected those who have traveled or live in the middle east. Saudi Arabia is the source of most of the cases.
On Tuesday, a man died in France after contracting MERS. There have been 49 confirmed cases worldwide.
The virus was first identified in humans in September.
Dr. Margaret Chan, head of the WHO, said, "We understand too little about this virus when viewed against the magnitude of its potential threat. We do not know where the virus hides in nature. We do not know how people are getting infected."
"Until we answer these questions, we are empty-handed when it comes to prevention. These are alarm bells. And we must respond."
She said the virus is a "threat to the entire world."
People infected with it had traveled to Qatar, Saudi Arabia, Jordan or Pakistan. There were also cases in Britain and Germany.
Last week, a case in Tunisia was revealed.
They believe the virus spreads mainly from person-to-person but have not confirmed this yet. They think the initial transmission came from animal to human.
French authorities have been handing out leaflets at airports to warn travelers to the middle east that they should wash their hands and limit contact with animals.