The Centers for Disease Control and Prevention has launched a multistate public health investigation after at least 12 people were exposed to a dog, imported from Azerbaijan by a rescue group, that tested positive for a rabies variant.

The dog was among a group of 33 canines and one cat that arrived at Chicago O’Hare International Airport on June 10. None of the other animals have tested positive, but all are considered to have been exposed, the CDC said in a statement. Travelers through O’Hare and those in the main cabin of the plane they arrived on are not at risk, health officials said.

According to testing by the CDC, the dog was infected with rabies before it arrived in the United States. Other animals in the shipment were transported to California, Illinois, Indiana, Michigan, New Jersey, New York, Ohio and Pennsylvania.

The dog, a 6-month-old mixed-breed puppy, was living with a family in Chester County, Pa., when they noticed it began acting strangely. The dog was later euthanized, according to the Pennsylvania Department of Health. The rabies test, which can only be conducted by examining the brain after an animal is euthanized, showed the animal was positive with a canine rabies variant that is highly transmissible from dog to dog.

“This virus variant is present in a lot of other countries, and it took us decades to get rid of it here,” Ryan Wallace, a veterinary medical officer with the U.S. Public Health Service who also leads the rabies epidemiology unit at the CDC, told The Washington Post on Saturday.

The news comes a month before a year-long CDC ban on imported dogs from roughly 100 countries considered at high risk for rabies is scheduled to take effect; Azerbaijan is among the nations on the CDC’s list.

CDC investigators are working with the rescue group to identify all the places the exposed animals went, noting that some were taken to rescues and foster homes. The agency did not name the organization involved.

The detected variant was eradicated in the United States in the 1970s, but reemerged in the 1990s as dogs and coyotes near the U.S.-Mexico border mixed, Wallace said.

“It took us about 50 years of getting vaccination laws and brick-and-mortar veterinary infrastructure in place,” Wallace said. “Our vaccine coverage of dogs in the U.S. over about 50 years got very high, and we were able to push out that dog variant.”

“When [the canine variant] was here in the ’40s, ’50s and ’60s, it was killing hundreds of people a year,” he added.

The canine variant that rapidly transmits from dog to dog is responsible for 59,000 human deaths a year — mostly in African and Asia — and is usually acquired from a dog bite, Wallace said.

Wallace said the canine variant is detected in the United States “every few years,” typically when a patient is bitten by a rabid dog while overseas and doesn’t get treatment. “When dogs get it, it’s always been from fraudulent paperwork,” he said.

The other exposed animals from Azerbaijan will be put in quarantine to make sure the variant doesn’t spread further, Wallace said.

The situation, he said, underscores the importance of getting family pets vaccinated for rabies, even if someone is not adopting a dog from overseas.

“If your dog isn’t vaccinated and it gets exposed, the options aren’t fun,” he warned. “It’s either your dog will need to be euthanized out of [an] abundance of caution, or it will have to go into a long-term quarantine where they won’t be allowed to have human or animal contact. It won’t be a good outcome for your animal.”

About 40 to 60 dogs in the United States are infected with rabies each year from a wildlife variant, meaning a dog contracted the virus from a wild animal like a raccoon or a bat, he said. That variant is not as transmissible between dogs like the eradicated canine variant.

Regardless of which variant an animal contracts, “a dog or a cat with rabies that is shedding the virus in its saliva will look sick very soon,” Wallace said.

Rabies is treatable in humans if detected quickly, but by the time a human or an animal begins to show clinical symptoms like excessive salivation, abnormal behavior and fear of water, it’s almost always fatal.

A teenage girl in Wisconsin who was bit by a rabid bat in 2004 and did not immediately seek treatment is among the few people who have survived without medical intervention. As of 2020, only 29 people worldwide are known to have survived untreated rabies.

Not only is the presence of rabies a significant public health threat, it can cost the federal government between $215,000 and $509,000 to investigate, the CDC said in a statement. Wallace expects the current case will be on the high end, given the number of humans and animals that have already been confirmed exposed.

The dog euthanized in Pennsylvania is the fourth rabid dog to be imported from a country with a high rabies risk since 2015, according to the CDC.

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