A tragic and rare instance of rabies has unfolded in Chicago, Illinois. Health officials reported this week that a young pet puppy developed the fatal infection—the first such case documented in the state in over 30 years.
The Illinois Department of Public Health disclosed the case in an emailed December 22 memo sent widely to local health departments, animal control centers, and veterinarians. The dog had recently bitten someone and was euthanized after its behavior continued to worsen, after which it was tested for rabies. It’s not clear where or when the dog was exposed to the virus, though it was vaccinated against rabies earlier in the year.
“Currently, the source of rabies for this dog is under investigation,” the IDPH stated in its memo.
Rare but fatal
According to the IDPH, the less than one-year-old dog is thought to have originated from a litter somewhere in the Southeastern U.S. (the IDPH initially believed that it came from Florida but does not any longer). The dog was sent from a rescue group in Florida to a fellow group in Chicago in May, where it was adopted by a local family.
Unfortunately, the dog had a history of behavioral issues, and on December 11, it bit someone. Rabies wasn’t suspected as a cause for the bite at first, since the dog was vaccinated in June. But due to state law, the dog had to be observed for at least ten days. By December 16, its behaviors had grown increasingly erratic and included growling, snapping, barking, and anxiety. On December 18, it was euthanized and subsequently tested for rabies (the gold standard test can only be done using post-mortem brain tissue); a day later, the test came back positive.
Rabies can infect just about every mammal and is usually transmitted through direct contact with infected saliva from bites and scratches. The virus typically makes its way to the spinal cord and brain, where it will eventually cause a variety of neurological symptoms; some of these symptoms, such as increased aggression and saliva production, then help the virus spread to other animals. In humans and many other animals, the infection is almost always fatal once symptoms emerge.
While variants of the virus continue to routinely circulate among wildlife, rabies is exceptionally rare in humans and our companion animals throughout most of the world, thanks to widespread vaccination programs for pets and livestock. The vaccine is also used as part of a treatment to prevent rabies symptoms in a person already exposed to the infection, along with donated antibodies.
The dog variant of rabies was officially eliminated from the U.S. in 2007, though cases transmitted from imported dogs or wildlife can still occur. According to the IDPH, this is the first dog rabies case recorded in the state since 1994 and the first such case in Cook County since before 1964. Annually, fewer than 10 people in the U.S. die from rabies.
A mystery infection
Given the dog’s vaccine status, it’s still a mystery as to why it became sick.
Vaccination is highly effective against rabies, but it can take up to 28 days following the initial vaccine for an animal to be fully immunized. That leaves open the possibility the dog was exposed during that window of vulnerability. It’s also possible the dog was infected prior to its vaccination and that the vaccine simply was too late to prevent the infection from progressing further. The incubation period (from exposure to illness) of rabies in animals is typically between 20 and 60 days but can sometimes extend to a year, the IDPH noted in its memo.
Another important question is where the infection originated. The dog’s owners reported no recent contact with any wild animals, including bats, the only wildlife source of rabies recently documented in the state. The officials are now testing whether the dog’s rabies is a match for variants found in bats, raccoons, and foxes.
The memo does not disclose whether the person bitten by the dog received post-exposure rabies treatment. But officials say they are evaluating any people in contact with the dog to determine if they should seek treatment. Local animal control officials are also following up with the owners of littermates to the dog, as well as owners whose dogs recently came into contact with it, including at a doggy day care. Vaccinated dogs potentially exposed to rabies are typically given a booster shot and closely monitored at home for 45 days.
This case, tragic as it is, highlights why rabies vaccines are important for veterinarians and their staff, the IDPH said in their memo. “It is also a reminder of the importance of keeping pet rabies vaccinations up-to-date to reduce the risk of rabies,” the agency added.
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