Rabies

TL;DR. Rabies is a rapidly progressive, fatal viral infection of the nervous system in dogs and cats that is transmitted through bites and is entirely preventable through vaccination.

The rabies virus travels from the site of a bite wound along the peripheral nerves to the spinal cord and brain.

What is it?

Rabies is a highly infectious, rapidly progressive, and fatal viral disease that attacks the central nervous system of mammals, including dogs, cats, and humans. Scientifically classified as a viral encephalomyelitis, the disease causes severe, irreversible inflammation of the brain and spinal cord. Because rabies is a zoonotic disease—meaning it can be transmitted from animals to humans—it is regarded as one of the most significant public health threats in veterinary medicine.

When an animal is bitten by a rabid carrier, the virus introduced via saliva does not immediately enter the bloodstream. Instead, it replicates locally in the muscle tissue before invading the local nerves. From there, the virus travels slowly along the nervous system up to the spinal cord and eventually reaches the brain. Once the virus gains access to the brain, it multiplies rapidly, causing acute neurological decline, and spreads to other tissues, most notably the salivary glands, where it can be transmitted to another victim through a bite.

For pet owners, understanding rabies is not just about protecting a single pet; it is a matter of community safety. Because there is no cure once clinical signs appear, and because the disease is almost always fatal, strict adherence to veterinary guidelines and local laws regarding rabies is vital.

Causes & risk factors

Rabies is caused by the rabies virus, a member of the Lyssavirus genus. The primary route of transmission is through the saliva of an infected animal, almost always introduced via a bite wound. Less commonly, transmission can occur if infected saliva comes into direct contact with an open scratch, wound, or mucous membranes (such as the eyes, nose, or mouth).

In the wild, the virus is maintained in reservoir species, which vary by geographic region but commonly include raccoons, bats, skunks, foxes, and coyotes. Any domestic dog or cat that is unvaccinated and has outdoor access is at high risk of exposure if they encounter these wild animals.

There are no breed predispositions for rabies; any dog or cat, regardless of breed, age, or size, is fully susceptible to the virus if they are unvaccinated and exposed. The single most significant risk factor for contracting rabies is the lack of up-to-date vaccination.

Signs to watch for

The time between the initial bite and the first appearance of clinical signs is known as the incubation period. This period is highly unpredictable. As noted in a leading veterinary internal medicine reference:

"The incubation period from the time of the bite to the onset of clinical signs is extremely variable (1 week to 8 months), with average incubation 3 to 8 weeks. Once neurologic signs develop, the disease is rapidly progressive, with death occurring within 7 days in most animals. Rabies can have a wide range of clinical signs, which makes it difficult to differentiate from other acute progressive e[ncephalomyelites]"

Once the virus reaches the brain and clinical signs begin, the disease progresses with devastating speed. The symptoms are traditionally divided into two forms—the "furious" form and the "paralytic" (or "dumb") form—though pets may exhibit signs of both.

Common Signs

• Licking or chewing at the inoculation site: Pets often obsessively bite, scratch, or lick the original wound where they were bitten.
• Excitability and nervousness: Normally calm pets may become suddenly hyperactive, anxious, or easily startled.
• Apprehensiveness and irritability: Affected animals may show sudden, unexplained changes in temperament, becoming fearful or aggressive.
• Incoordination: Weakness, wobbliness, and a loss of motor control (ataxia) develop as the virus damages the spinal cord and brain.
• Generalized lower motor neuron (LMN) paralysis: Progressive weakness that eventually leads to the inability to move the limbs.

Occasional Signs

• Excessive drooling and difficulty swallowing: The virus paralyzes the muscles used for swallowing, causing saliva to pool in the mouth.
• Dropped jaw: The muscles holding the lower jaw closed lose tone, leaving the mouth hanging open.
• Hoarse vocalization: Paralysis of the vocal cords alters the sound of the pet's bark or meow.
• Snapping at imaginary objects: Also known as "fly-biting," this indicates severe neurological dysfunction and hallucinations.
• Biting at the cage or surroundings: Pets in the furious phase may aggressively attack inanimate objects.
• Diminished facial sensation and cranial nerve paralysis: Loss of normal reflexes in the eyes, eyelids, and face.
• Generalized seizures: Severe electrical disturbances in the brain leading to full-body convulsions.

Sudden behavioral changes, such as apprehension, irritability, and tense posture, are common early signs of rabies.

How vets diagnose it

Diagnosing rabies in a living animal is exceptionally challenging. Because the clinical signs mimic many other neurological conditions—such as canine distemper, advanced lead poisoning, or brain tumors—a definitive diagnosis cannot be made solely on a physical exam. As a leading reference states:

"Any unvaccinated animal with an acute, rapidly progressive course of neurologic disease should be suspected of having rabies. Ancillary testing should be performed with caution, minimizing exposure of personnel. CSF analysis reveals increased mononuclear cells and protein concentration, as might be expected with any viral encephalomyelitis."

Because rabies is a zoonotic hazard, veterinarians must exercise extreme caution when handling suspected cases to avoid exposure to saliva or spinal fluid.

There are three primary diagnostic methods:

1. Postmortem Immunohistochemical Demonstration (Gold Standard): The only definitive way to diagnose rabies is by examining brain tissue after the animal has died or been humanely euthanized. This test, typically performed using a direct fluorescent antibody (DFA) technique, looks for rabies virus antigens in the brainstem and cerebellum.
2. Cerebrospinal Fluid (CSF) Analysis: In living animals where rabies is suspected but not yet confirmed, analyzing the fluid surrounding the brain and spine may show elevated protein and mononuclear white blood cells. Rabies antibodies may also be elevated in the CSF compared to the blood. However, this test is not definitive and carries a high risk of exposure for veterinary staff.
3. Skin Biopsy: A biopsy taken from the nape of the neck or the maxillary sensory vibrissae (the whisker area) can sometimes detect rabies viral antigen in the nerves surrounding hair follicles. While useful in some specialized scenarios, it does not replace the necessity of postmortem testing for definitive confirmation.

Treatment options

There are no effective antiviral treatments, cures, or therapies for rabies once clinical signs appear. Because of the extreme risk of transmission to veterinary staff, pet owners, and the public, supportive care is not attempted for animals showing signs of rabies.

If a pet is suspected of having rabies, local public health laws dictate the protocol. Unvaccinated animals that have been exposed to a known rabid animal are typically subject to strict quarantine or immediate, humane euthanasia to prevent further spread of the virus.

Prognosis

The prognosis for rabies is grave. Once clinical signs of the disease manifest, the infection is uniformly fatal, with death or the necessity of euthanasia occurring within 7 days of the onset of neurological signs. There is no recovery, and long-term management is not possible.

Prevention

While rabies is untreatable, it is entirely preventable. Vaccination is the single most important defense against this virus.

• Routine Vaccination: Dogs and cats should receive their initial rabies vaccine between 12 and 16 weeks of age, followed by a booster one year later, and subsequent boosters every one to three years depending on local legislation and the specific vaccine used.
• Minimize Exposure: Keep cats indoors and keep dogs on a leash during walks. Avoid letting pets roam unsupervised, especially in wooded areas where they may encounter wild reservoir species.
• Wildlife Control: Do not leave pet food outside, which can attract wild animals to your yard, and ensure trash cans are securely sealed.
• Immediate Action Post-Exposure: If your vaccinated pet is bitten by a wild animal or a suspected rabid domestic animal, contact your veterinarian immediately. They will administer a rabies booster vaccine to stimulate the pet's immune system and guide you through the legally required observation period.

When to call your vet

If your pet is bitten or scratched by a wild animal, or by any domestic animal with an unknown vaccination history, you must contact your veterinarian and local animal control authorities immediately.

Additionally, contact your vet immediately if your pet exhibits any of the following red-flag signs:

• Sudden, unexplained changes in behavior, such as extreme aggression or unusual fearfulness
• Unexplained drooling, difficulty swallowing, or a dropped jaw
• Progressive loss of coordination, stumbling, or weakness in the hind legs
• Seizures or snapping at the air

Sources

• Small Animal Internal Medicine, 5th Edition, pages 1077-1078.