Last week, the CDC announced the death of a 7 year old Texas boy from Rabies virus infection. I was saddened for his family, and thought this would be a good time to remind ourselves about this virus. As of October, 14 cases of rabies had been identified in the State of Wisconsin; all 14 were in bats. It's still infecting animals, and therefore a risk to humans, too.
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).
Once neurologic signs are present, progression is rapid, and most animals will be dead within several days. The CDC report says that the boy was bitten by a bat 2 months prior to onset of signs and that he became deceased after 22 days of clinical signs.
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 other rabid, or wild, animals.
Diagnostic Tests
Key point: 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. Due to the neurotropic nature of rabies it can remain undetected by the immune system and therefore cause a negative (false negative) RFFIT antibiotic result.
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! Rabies virus infection is something I think about daily and is one of the more daunting zoonotic diseases we are faced with. Please reach out if you have any questions!
Please note: If you use my services for live or video neurology consultations, fees are changing January 1, 2023. Please email for an updated fee schedule.
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