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Rabies in Dogs and Cats
Emily Beeler, DVM, MPH and Karen Ehnert, DVM, MPVM, DACVPM

Veterinary Public Health Program, Los Angeles County Department of Public Health, Los Angeles, CA, USA

Etiology and Pathophysiology When increased inflammation and damage do occur in
the CNS, they are usually found in patients in which par-
The rabies virus is an enveloped, single‐stranded RNA alytic clinical signs predominated. The total amount of
virus in the family Rhabdoviridae and the genus virus in the brain tends to be significantly higher in cases
Lyssavirus. There are 16 known lyssaviruses worldwide of encephalitic, “furious” rabies than in cases of paralytic,
capable of causing rabies‐like symptoms in mammals. “dumb” rabies.
Bats are the reservoir for most of them. Rabies virus itself Some details of what happens at the molecular level of
is by far the most prevalent lyssavirus, and the only one rabies pathogenesis remain a mystery. The rabies virus
known to exist in the Americas. Rabies has the highest has an uncanny ability to evade early recognition and
mortality rate of all known infectious diseases. clearance by the immune system, and to preserve the
Rabies is usually transmitted by the bite of a rabid ani- health of cells of the nervous system throughout most of
mal. It may also be transmitted when virus‐laden saliva is the infection. In laboratory studies, rabies virus strains
introduced into mucous membranes. Theoretically, that stimulate a significant immune response are less
scratches may transmit the virus, if the claws are con- pathogenic than those that suppress it.
taminated with fresh infectious saliva, but this mode of
spread is very rare in people. Because the virus may be
present in tissues throughout a rabid animal, exposure Epidemiology
may occur during necropsy. Rabies has occasionally
been spread by corneal and internal organ transplanta- Over 60 000 people die worldwide from rabies each year.
tion, transplacentally, through aerosolization in closed The vast majority of rabies victims are children who were
spaces such as caves, and by ingestion of infected tissues. infected by bites from rabid dogs. Most cases occur in
Because it is readily destroyed by UV light, desiccation, countries where rabies vaccination rates for dogs are
and most disinfectants, the rabies virus is not effectively below 50%, primarily in Asia and Africa.
transmitted by fomites. The human death toll from rabies is much lower in
When the rabies virus first enters the body, it multi- countries where animal control policies are well estab-
plies at a very low rate in a small amount of muscle cells lished and vaccination of pets is widespread. Over the
and fibrocytes, and curtails the local immune reaction by past two decades in the United States, an average of
inhibiting type I interferons. The majority of the incuba- three people per year died from rabies. Typically, the
tion period, which can last for 3–12 weeks or more in cases occurred after a person failed to obtain timely
dogs and cats, likely passes with the virus localized at the rabies postexposure prophylaxis, often due to lack of
site of entry. The virus then enters the nervous system awareness about the risk of rabies. About 70% of the
through a peripheral motor nerve, and is drawn up the cases were caused by bat bites, and most others were
axon at a rate of about 100 mm per day. Once the virus caused by a dog bite inflicted while the person was visit-
reaches the neuronal cell body, it multiplies and dissemi- ing another country.
nates rapidly, although unevenly, throughout the central The primary reservoirs for rabies are bats, domestic
nervous system (CNS). Histologic analysis of brains dogs, raccoons, skunks, foxes, mongooses, and jackals.
from rabies victims typically reveals little tissue damage. In the past decade, 6000–7000 rabid animals per year

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical