Classification: (1)
Group- Group V
Order- Mononegavirales
viruses with non-segmented, negative stranded RNA genomes
Family- Rhabdoviridae
viruses with a distinct bullet shape
Genus- Lyssavirus
Species- Rabies virus
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Structure:
pic (1)
  • 180 nm long and 75 nm wide (1)
  • All rhabdoviruses have 2 major structural components (1):
         1) helical ribonucleoprotein core (RNP)
         2) surrounding envelope
  • In the RNP, genomic RNA is tightly encased by the nucleoprotein (1)
  • The glycoprotein forms approximately 400 trimeric spikes which are tightly arranged on the surface of the virus (1)
  • The matrix protein is associated with both the envelope and RNP and may be the central protein of rhabdovirus assembly (1)
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Replication:
pic (1)


Replication of the rabies virus follows the progression for RNA virus replication described in the virus overview.
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Transmission and Infection (4):
pic is (4)
Transmission
  • The virus is harbored in saliva and is often transmitted via animal bites (rare cases: corneal/other tissue transplant, contact of infected saliva with mucosal membranes or an open wound in the absence of a bite, inhalation of aerosolized rabies virus)
Infection
  • The virus binds to nerve or muscle cells at the site of the bite via nicotinic acetylcholine receptors
  • It remains there for a prolonged period of time (several months)
  • The virus multiplies in the muscle cells at the site of the bite without showing symptoms (incubation phase)
  • Next, the virus moves a long nerve axons to the CNS using retrograde transport
  • The virus arrives a the dorsal root ganglia and spinal cord then from there spreads to the brain (prodromal phase)
  • Brain cells infected: cerebellum, purkinje cells, hippocampus, pontine nuclei
  • Brain infection leads to encephalitis and neural degeneration, eventually leading to coma and death (neurological phase)
  • During the neurological phase, the virus spreads from the CNS to the skin, eye, various other sites and the salivary glands via neurons
Symptoms in an Animal(5):
Stage 1:
  • loss of appetite
  • a change in normal behavior, such as appearing unusually tame around strangers
Stage 2: mad dog stage, 2-4 days, aggressive and erratic behavior

  • constantly barking or growling
  • no fear of normal natural enemies
  • attempting to attack and bite anything that comes near, including inanimate objects
Final stage: paralytic stage, 2-4 days
  • animal appears to be choking
  • foaming at the mouth
  • dropping of the lower jaw (dogs)
  • paralysis of the jaw, mouth and throat muscles
Conservation Status (4):
  • Canine rabies is most prevalent in Latin America, Asia and Africa
  • Recently in the U.S. (1990-2004) 35 of 47 cases have been associated with bat rabies and 2 were dog/coyote-like strains acquired in the U.S. and 10 were dog/coyote-like strains acquired outside the U.S.
  • Immunization of pets and quick response to bites from suspicious animals may explain why bat-transmission has been the predominant mode of transmission in recent years
  • In the U.S., vaccination of animals has reduced the rate of the human disease to one case per year
  • In India, there are 25,000 cases of human rabies per year
  • In South America, rabies transmission by vampire bats poses a major problem for the cattle industry

Interesting Facts (3):
  • Humans have been infected in rare cases after breathing in the air of bat caves
  • The latin word rabies means madness and the sanskrit word rabhas means "to do violence"
  • Until 1885 when the rabies vaccine was developed, all human cases of rabies were fatal