This disease, known to infect both humans and animals and dating back to the 23rd century BC, is also referred to as “mad dogs” and is considered one of the oldest known zoonotic infectious diseases.The causative agent is a neurotropic virus belonging to the genus Lyssavirus within the family Rhabdoviridae.

This virus is bullet-shaped, enveloped, single-stranded RNA virus, and three known strains exist:

• Street virus
• Fixed virus (this strain does not show affinity for the salivary gland)
• Flury strain
  

Although rabies infection is clinically always fatal, the virus is easily inactivated by heat, light, common disinfectants, and ultraviolet radiation.

Etiology

Multiple transmission routes for rabies infection have been identified. The most common route is via bite wounds, when a susceptible animal is bitten by an infected animal. Additionally, transplacental and airborne transmission have also been documented.

The incidence of rabies in dogs is highly consistent with its incidence in wildlife. Moreover, cats play a more significant role than dogs in the transmission of rabies to humans.

Globally, the main hosts of rabies include dogs, foxes, beavers, raccoons, bats, wolves, cats, jackals, mongooses, and cattle. Furthermore, bats are unique as they can survive rabies infection without fatal outcomes and have been associated with human rabies for more than a decade.

Pathophysiology

Clinically, rabies is classified into two main types: furious (aggressive, hyperreactive) and paralytic (dumb). However, the clinical manifestations vary widely, making a strict classification into only two types inappropriate.

In dogs, the incubation period following exposure to the virus is typically 3–8 weeks, but incubation periods up to 6 months have been reported. 

Factors influencing incubation include host genetics, viral load, acetylcholine receptor concentration in skeletal muscles, distance of the bite site from the central nervous system, susceptibility, and viral strain.

Clinical Signs

In the early stages of rabies infection in dogs, signs such as withdrawal, irritability, and anxiety appear. In cases with a bite wound, pruritus at the inoculation site is observed. Typical clinical disease develops within 1–10 days after the onset of symptoms.

• In furious rabies, dogs exhibit progressive restlessness. Hyperexcitability occurs in response to visual and auditory stimuli. Pica and attempts to bite imaginary objects may also be observed. In the final phase, disorientation, loss of consciousness, tonic-clonic seizures, and muscle spasms develop.

• In paralytic (dumb) rabies, the earliest typical signs are cranial nerve damage and lower motor neuron paralysis. Dogs exhibit excessive salivation and dysphagia, resulting in the characteristic “open jaw” appearance. Changes in barking tone occur due to laryngeal paralysis. Ultimately, death occurs within 2–4 days due to respiratory failure following paralysis.

Differential Diagnosis and Diagnosis

In an unvaccinated dog, the presence of neurological disorders accompanied by behavioral changes is the primary clue for differential diagnosis. Diseases with clinical signs similar to rabies include canine distemper virus (CDV), sepsis, tetanus, botulism, various causes of encephalitis, and intracranial neoplasms.

Although rabies may be suspected based on clinical signs, no sufficiently definitive antemortem diagnostic test exists.

The most widely used method today is the direct immunofluorescence assay (IFA) on nervous tissue. Other methods, though less sensitive, include histological identification of Negri bodies, PCR testing of nervous tissue, and mouse inoculation.

Treatment and Prognosis

No treatment or supportive care should be attempted in dogs suspected of rabies. Rabies infection in dogs is universally fatal.

Prevention

Rabies vaccines available for dogs are inactivated (killed) virus vaccines, and by law, they must be administered to all dogs.

The recommended earliest vaccination age is 12 weeks. The initial dose must be followed by a booster within one year. Subsequent vaccinations should be administered according to the manufacturer’s instructions and local regulations.

This blog post was written with reference to the YouTube video below and verified by Vet. Med. Kaan KAŞIKÇI.

Resources

SCHAER, M. GASCHEN, F. (2019) Clinical Medicine of Dogs and Cats. Konya, Türkiye: Nuri ALTUĞ, Last access date: 03.05.2024