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A Swiss tourist couple who thought they were doing a good deed caused an international incident when a bat they rescued turned out to have rabies, federal health officials said.

The pair were only tracked down and notified after officials at the Centers for Disease Control and Prevention opened channels usually reserved for infectious disease emergencies.

But rabies is almost 100 percent fatal and the CDC didn’t want to mess around.

“Two tourists were in Naples, Florida. They found a bat just outside of a grocery store,” said Dr. Ryan Wallace, a rabies expert at the CDC's National Center for Emerging and Zoonotic Infectious Diseases.

“They took the bat and they brought it to a local veterinary clinic and unfortunately didn’t leave any contact information at all. The bat died at the clinic and tested positive. (It) was reported to the state health department of Florida.”

That set off alarm bells. Rabies is the most deadly virus known, bats across the Americas carry it, and even the tiniest scratch can transmit it. People often don't realize they have been exposed.

Just days before, a 6-year-old boy in Florida had caught rabies via a bat scratch, and he later died.

But the veterinary clinic had not had a chance to get any official information about the couple who had turned in the bat.

“When they went to investigate, they realized the only information we had was that a couple with a foreign accent who may have been Swiss, in their 50s or 60s, dropped the bat off. And that was all we knew,” Wallace said.

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Related: Vaccine could have saved boy who died of rabies

Alerts on the local news did not flush out the couple, who, for all the CDC and local health authorities knew, had already gone back home.

“We kind of threw a Hail Mary,” Wallace said. The CDC reached out to Swiss authorities with “probably the least amount of information we have ever had: Two people that we think are Swiss, who might have been in Florida on vacation in Naples, Florida, might have touched a bat. Can you help us find them?” he said.

“Switzerland took that information, made a national press release.”

It worked.

Bats can carry rabies. Any bat found behaving in an unusual manner should be turned in for rabies testing. Gregorio B. Dantes Jr. / Sipa USA via AP

“Within five hours that couple self-identified themselves,” Wallace said. They said they both had handled the bat with bare hands. They have now been vaccinated against rabies.

Rabies still kills 55,000 or more people a year around the world, the World Health Organization says. In the past few months, two people have died from rabies in Florida — the 6-year-old boy, and an unidentified victim who died last October.

"Two people that we think are Swiss, who might have been in Florida on vacation in Naples, Florida, might have touched a bat. Can you help us find them?"

People who fear they’ve been exposed to rabies first get an injection of immune globulin — pre-made antibodies designed to grab any circulating virus right away. Then they get four doses over 14 days of a preventive vaccine, which boosts the body’s own immune response.

If people get vaccinated in time, before symptoms begin to show, the vaccine is 100 percent effective, Wallace said. Once symptoms begin, it is almost always too late.

“Between 40,000 and 60,000 people a year get the rabies vaccine — almost everyone who should,” Wallace said. “It is widely available. It’s one of the reasons we have so few human deaths from rabies in the United States.”

Because rabies is uncommon in Europe, the Swiss couple likely were unaware of the danger, Wallace said. They were lucky that health authorities went to such lengths to track them down.

“It’s crazy. We really did not think we could find these people,” Wallace said. “Luckily, the Swiss health authority came through.”

His advice: “Any interaction with wildlife you should be thinking rabies, no matter where you are.”

Any bat found behaving in an unusual manner should be turned in for rabies testing, Wallace said.