BASICS
- A lethal encephalitis caused by a neurotropic, single-stranded RNA virus in the family Rhabdoviridae, genus Lyssavirus
- Rabies is usually transmitted via salivary contamination of a bite wound. Historically, an animal may have been bitten by a dog, racoon, skunk, fox, or bat several months prior to the onset of signs, although most bite wounds are healed by the onset of neurologic signs
- The virus amplifies in muscle tissue before invading the peripheral nervous system. It is not known how the virus enters the peripheral nerves
- The virus moves to the CNS by axoplasmic flow and passes along neurons within the nervous system
- Systems affected—nervous
Any breed, sex, and age may be affected; however, smaller slower animals (donkeys) are at higher risk.
- The presenting signs of rabies virus infection can be extremely varied; however, in practice, many of the symptoms are surprisingly characteristic of the disease, particularly in the more advanced stages
- Most animals appear alert and anxious with progressive ataxia and characteristic odd vocalizations. Automutilation or mutilation of surrounding objects is extremely common. Typically animals target a specific body site and hold the bite for several minutes
- Early signs of the disease are more subtle and varied. Animals can present with colic, which presents obvious risks to veterinary personnel
- Classically, the syndromes are divided into a cerebral or furious form, the brainstem or dumb form, and the spinal cord or paralytic form. In practice these syndromes may overlap and the “dumb” form seems to be rare in equids
- Forebrain signs often include aggressive behavior, hyperesthesia, vocalization, sialosis, tenesmus, and convulsions
- In the dumb form, somnolence, dementia, stupor, opisthotonos, facial hypoalgesia, pharyngeal paralysis, excessive drooling, and ataxia occur
- The paralytic form is characterized by progressive ascending paralysis; monoparesis/plegia; truncal, limb, and perineal hyporeflexia and hypoalgesia; priapism; and altered frequency of miction; and urinary incontinence
- Self-mutilation is typical
- Once signs start, the clinical course is <14 days, but usually <5 days, and the animal dies in a mean period of 3 days
- Prodromal colic, lameness, anorexia, and hydrophobia may be recalled by owners
- Fever may occur independent of seizure activity
- Web Video 1 shows a donkey showing typical signs of the disease. Anxious alert expression, persistent automutilation usually of the same area, difficulty rising with ataxia evident on all four limbs.
- The disease is caused by serotype 1 rabies virus. This is a single-stranded RNA virus of the genus Lyssavirus and family Rhabdoviridae. There are 25 viruses in this family, but only serotype 1 is pathogenic
- Rabies has 2 cycles, which include canine (urban) and wildlife (sylvatic) rabies. Most wildlife vectors are small omnivores, such as skunks, raccoons, or foxes
- There is extension into domestic animals, which are essentially dead-end hosts
- Horses in enzootic areas are at risk
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS