Todayโs path rounds are on ๐ซ๐๐๐ข๐๐ฌ!
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
๐๐๐๐ข๐๐ฌ is a viral disease caused by a ๐๐ฒ๐ฌ๐ฌ๐๐ฏ๐ข๐ซ๐ฎ๐ฌ, which are viruses typically found in bats. Current evidence suggests that rabies virus developed initially in vampire bats, and later became adapted to carnivores.
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
All mammalian species are susceptible to rabies, which makes it somewhat unique!
๐๐จ๐ฐ ๐๐จ ๐๐ง๐ข๐ฆ๐๐ฅ๐ฌ ๐ ๐๐ญ ๐ข๐ง๐๐๐๐ญ๐๐?
Animals typically get infected by a bite wound from an infected animal. This is because rabies has a ๐ญ๐ซ๐จ๐ฉ๐ข๐ฌ๐ฆ (the virus seeking out a particular tissue) for the salivary glands, so the virus is shed in an infected animalโs saliva.
After infected saliva is transferred into a wound, the virus enters the surrounding muscle cells and begins to replicate itself. From there, it enters a local nerve and moves ๐ซ๐๐ญ๐ซ๐จ๐ ๐ซ๐๐๐ (up the nerve) until it reaches the brain. The brain is the virusโ preferred home, so it sets up shop and begins multiple rounds of replication. The virus then spreads back to the salivary glands to allow infection of other animals.
๐๐ก๐๐ญ ๐ก๐๐ฉ๐ฉ๐๐ง๐ฌ ๐ข๐ง ๐ซ๐๐๐ข๐๐ฌ ๐ข๐ง๐๐๐๐ญ๐ข๐จ๐ง?
Rabies typically has a very short clinical course, ranging from 1-10 days in length. Unfortunately, rabies is nearly always fatal for infected animals.
There are thought to be two different clinical forms of rabies. The first form is the โfurious formโ, which is the form that most people associate with rabies infection. In this form, animals show aggression, self-mutilation, irritability and anxiety. Carnivores with this form of rabies often exhibit ๐ฉ๐ข๐๐ (ingestion of non-food objects). The second form is the โdumb formโ, where animals exhibit ๐๐ญ๐๐ฑ๐ข๐ (difficulty walking), paralysis, excessive salivation and the inability to swallow. However, it is more likely that these are just progressive stages of the disease in most species.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
In general, rabies should be suspected any time a terrestrial animal is behaving abnormally, especially if they are showing neurologic signs like ataxia and paralysis. ๐๐ง๐ข๐ฆ๐๐ฅ๐ฌ ๐ฐ๐ข๐ญ๐ก ๐ฌ๐ฎ๐ฌ๐ฉ๐๐๐ญ๐๐ ๐ซ๐๐๐ข๐๐ฌ ๐ฌ๐ก๐จ๐ฎ๐ฅ๐ ๐๐ ๐๐ฎ๐ญ๐ก๐๐ง๐ข๐ณ๐๐ ๐๐ง๐ ๐ฌ๐๐ง๐ญ ๐๐จ๐ซ ๐ง๐๐๐ซ๐จ๐ฉ๐ฌ๐ฒ. This is because the preferred tissue for diagnosis is the brain, where the virus is most prevalent.
Typically, rabies is diagnosed using ๐ข๐ฆ๐ฆ๐ฎ๐ง๐จ๐๐ฅ๐ฎ๐จ๐ซ๐๐ฌ๐๐๐ง๐๐, where an antibody against rabies that has a molecule of fluorescent dye attached to it is introduced to a tissue. If the tissue contains rabies virus, the antibody will bind to the cell, displaying the dye and confirming the diagnosis.
However, pathologists also like to look at the tissue under the microscope (because weโre nerds), and one of the classic indicators of rabies are round ๐๐๐ข๐๐จ๐ฉ๐ก๐ข๐ฅ๐ข๐ (pink) structures called ๐๐๐ ๐ซ๐ข ๐๐จ๐๐ข๐๐ฌ within neurons. These structures actually contain the rabies virus and the proteins it produces! Cool.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ฉ๐ซ๐๐ฏ๐๐ง๐ญ๐๐?
The best method of prevention is routine rabies vaccination, particularly for animals that may come into contact with bats or small carnivorous wildlife. Because this disease also affects humans, prevention is critical to keep all of us, and our pets, safe!
๐๐ก๐จ๐ญ๐จ๐ฌ
1-3) Examples of Negri bodies seen at histology.
4) An example of ๐ข๐ฆ๐ฆ๐ฎ๐ง๐จ๐ก๐ข๐ฌ๐ญ๐จ๐๐ก๐๐ฆ๐ข๐ฌ๐ญ๐ซ๐ฒ, which works similar to immunofluorescence, demonstrating the virus within neurons.
5) A video of a horse with rabies exhibiting self-mutilation behaviour.
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Maxie, G. Jubb, Kennedy and Palmerโs Pathology of Domestic Animals, Volume 1. Sixth Edition.
Rupprecht, C.E. Rabies. Merck Veterinary Manual, 2020.
Photos 1-4 courtesy of Noahโs Arkive.
Video courtesy of Katie LoPresti.
