RABIES

Family - Rhabdoviridae
Genus - Lyssavirus

    The rabies virus is a single stranded, enveloped RNA virus.  This is a highly fatal virus that has the potential to infect all animals and humans.  The virus is fragile and is inactivated with standard disinfectants.  

    Rabies vaccination is not a normal component of a cow-calf  vaccination program.  However, because of the zoonotic risk and the highly fatal outcome it should be noted that in endemic areas where clinical cases of rabies have been reported, there are vaccines that can be added to a herd’s annual vaccination regime.  

    Canada’s endemic areas include southern Ontario, which makes up 85% of reported cases, and the prairie provinces.  Prairie province wild life reservoirs include bats, skunks, raccoons, and foxes.  Bats are an important vector as they are sub-clinical carriers.1


Clinical Signs:
    Rabies is ALWAYS FATAL.  It is also a zoonosis is a major risk.  There is no characteristic pattern associated with the clinical signs of rabies as they will vary from case to case.  Some of the more common clinical findings include:   - Excessive Salivation        - Hyperesthesia/hyperexcitability   
                                     - Muzzle tremors                  - Aggression
                                     - Behavioural changes        - Pharyngeal paralysis   
                                     - Vocalization    

Clinical signs can be grouped into two forms:
Furious Rabies  (70% of cases)
  • animals may appear tense,
  • animals may be hypersensitive to sound
  • animals may appear uncoordinated
  • animals may have hoarse vocalization
  • bulls may have sexual excitement
  • animals might attack other animals or inanimate objects
  • In the end, animals will suddenly collapse in a paralyzed state and death occurs within a few hours
Paralytic Form
  • Knuckling of hind fetlocks
  • Swaying and incoordination of hind quarters
  • Deviation and flaccidity of tail to one side
  • Yawning movement (voiceless attempts to bellow)
  • Animals end in recumbency and death usually follows 48 hours later


Transmission and Pathogenesis:
    A bite from an infected animal is the major source of transmission.  Studies have shown that it is possible to become infected via fresh saliva contaminating a skin wound but this is minimal.2  The mode of transmission should always be taken into thought when manipulating the mouth of a potentially infected animals during treatment or examination.  


Virus inoculated during bite from infected animal

then the

Virus replicated in local muscle near the bite wound
(The incubation period depends on the distance of the bite to the Central Nervous System)

then the

Virion enters peripheral nervous system

then the

Replicates in dorsal ganglion

then the

Virus rapidly ascends in spinal cord

then the

Infection of the spinal cord, brain stem, cerebellum, and other structures of the Central Nervous System

then the

Virus descends via nervous system to the eyes, salivary glands, skin and other organs
(last two are responsible for the clinical signs seen)2


Diagnosis: 
DIAGNOSTIC TEST
TISSUE SAMPLE
Histology for Light Microscope and Immunohistocompatibility
½ the midsagitally sectioned brain, cervical spinal cord (including the root ganglia), and parotid salivary gland)
Virology for FAT, ISO, BIOASSAY ½ of the midsagitally sectioned brain and cervical spinal cord
                                                                                                                                                                                                                1                                                                      


Treatment and Control: 

    There is no treatment.  If a bite has been witnessed, irrigation with 20% soap solution or Zephiran may prevent the establishment of the infection.

    There are killed vaccinations available in Canada that can be adapted into a producer's annual vaccination protocol as a type of control management.  (SEE VACCINATIONS AVAILABLE)
   
    The Compendium of Animal Rabies Control is annually publish by the National Association of the State Public Health Veterinarians Inc. in Canada and United States.  Here recommendations for immunization procedures, rabies control (control of wild animals), and post-exposure management are provided. 1  

Rabies is a reportable disease in Canada.

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