Rabies Virus Infection in Dogs
I'm hopeful that most of you heard of the dog diagnosed with a Rabies virus infection in Chicago, Illinois in December 2025. If not, here is the story: (https://www.cookcountyil.gov/news/cook-county-department-animal-and-rabies-control-confirms-rabies-positive-dog). This is a sobering reminder that Rabies virus is still out there and that being vaccinated does NOT eliminate the possibility of a rabies virus infection. This feels like a good time to review our knowledge and resources for Rabies virus infections, don't you think?
Etiology
Rabies is a neurotropic rhabdovirus that causes fatal infection in dogs, cats and (usually) humans. Infection is caused by inoculation from saliva by means of a bite. The virus then spreads into the CNS via peripheral nerves. Once the brain is infected, the virus spreads back out through peripheral nerves to the salivary glands – at this point, the animal can transmit rabies.
Signalment
Any dog, cat, horse, cow, HUMAN
Clinical Signs
Two syndromes are described:
Furious syndrome (forebrain signs) - seizures, mentation changes, aggression/sedation, visual changes.
Paralytic syndrome (lower motor neuron signs ascending from the site of the bite). Paralysis in one or more legs can be an indication of ascending infection. This means a paraplegic dog could be considered for rabies observation if they are NOT vaccinated. Be aware!
Once neurologic signs are present, progression is rapid, and most animals will be dead within several days but it has been reported to last up to 3 weeks in a few pets. Remember, the ONSET to clinical signs after exposure can be much longer.
Rabies should be considered as a differential diagnosis in any animal with acute onset, rapidly progressive neurologic disease especially if there is a poor vaccination history or exposure to wild animals.
Diagnostic Tests
Key point: A definitive diagnosis can only be achieved postmortem, and requires fluorescent antibody staining of brain tissue to demonstrate rabies antigen. A serum RFFIT (Rapid fluorescent foci inhibition test) can be performed to evaluate for evidence of previous vaccination however it should NOT be used to make a diagnosis of active rabies infection. One of the cases I evaluated had a negative RFFIT test and was confirmed to have the rabies virus on necropsy. Due to the neurotropic nature of rabies it can remain undetected by the immune system and therefore cause a negative (false negative) RFFIT result.
What do you do if you've been exposed? Contact your local heath department immediately.
What do you do if you have a patient that you suspect has a rabies virus infection? Contact your field vet (Wisconsin: https://datcp.wi.gov/Documents/AHVetsMap.pdf)
Further reading
If you're interested in reading about a case of Rabies virus infection please check out this article. https://doi.org/10.5326/0390547. I saw this case a number of years ago, but the disease hasn't changed much in 20 years!
Thanks for reading! A rabies virus infection is something worry about for those of you out there on the front lines. Be aware, be cautious, and when in doubt - put on PPE!! Please reach out if you have any questions.
Other good resources:
The Wisconsin Rabies Algorithm: (for exposure or sick animals) https://www.dhs.wisconsin.gov/rabies/algorithm/algorithmcategories.htm
Illinois Rabies information: https://www.ilga.gov/commission/jcar/admincode/008/00800030sections.html