I read some sobering data recently, produced by the CDC, pertaining to Rabies. They published a table of Human Rabies virus infections in the USA and Puerto Rico between 2000-2022. No cases were reported in 2022. Over the remaining 21 years, 57 cases were identified ranging in age from 7 to 87 years old. The source of infection was listed as "contact", "bite", "unknown" or "organ transplant" (Yeah, this one was unexpected to me!). One individual survived but the remaining 56 cases were, not surprisingly, all fatal. Reading this table reminded me that we haven't talked about Rabies on TidBit Tuesdays for awhile (actually since 2022!). As your friendly neighborhood neurologist, I feel strongly that we should have this conversation so please read on.
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)
Paralytic syndrome (lower motor neuron signs ascending from the site of the bite). 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. Most of the individuals on the CDC table were deceased within 3 weeks of their noted infection date.
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 the State Veterinarian (Dr. Yvonne Belay at 608-516-2664)
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