Exotic Diseases

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Species Infected

can affect all warm blooded animals

Clinical Signs

• incubation 3-8 weeks; may range from 10 days to 9 months

Dog

     3 phases : prodromal/acute neurological/paralytic

• prodromal phase
• nonspecific signs occur including fever, anorexia, malaise
• infection site may be pruritic

• acute neurological phase
• clinical course 3-7 days
• reversal of demeanour
• two syndromes, some dogs may alternate between the two

          1.  Dumb rabies

• 75% of cases
• rarely bites, lethargic, hides
• muscle tremors
• paralytic phase develops before death

          2.  Furious rabies

• clinical course is longer
• aimless wandering, blunders into objects
• restless, excitable, irritable
• bites people, animals
• attacks inanimate objects
• glazed appearance
• low pitched, hoarse bark


• paralytic phase
• develops with muscle paralysis salivation, convulsions
• lower jaw hangs, tongue protrudes and head droops
• ataxia, hindquarter paralysis, death shortly follows

Cattle

• variable clinical signs which may be either mild or furious form
• restless, aggressive, paws ground, abnormal bellow
• may have decreasing intervening normal periods
• choking may resemble pharyngeal foreign body
• marked sexual excitement
• hindquarter paresis with knuckling fetlocks
• drooling of saliva, yawning or voiceless bellowing, general paralysis

Horses

• most show paralytic form
• if furious - violent and manic
• blind charging
• sudden falling
• chewing of foreign material or itself
• development of terminal paralysis
• mortality 100%

Lesions

• none grossly
• histopathology: a variable nonsuppurative encephalomyelitis
• presence of intracytoplasmic Negri bodies in neurones

Pathogenesis

• transmission generally by contamination of fresh wound with infected saliva
• oral/respiratory transmission rare, but possible
• not every case of exposure leads to disease in humans
• minor wounds 0.1%
• severe wounds 60%
• virus remains at inoculation site for significant part of incubation period
• multiplication in local myocytes
• virus penetrates nerve endings by binding at acetylcholine receptors and passes via peripheral nerves to brain
• replicates in all parts of brain
• virus then spreads by neural pathways to other organs including salivary glands
• virus excretion in saliva may occur just before onset of clinical signs

Aetiology

• Lyssavirus (Rhabdoviridae)
• pathogenicity
• a number of variants and species adapted strains exist but all are relatively homogeneous antigenically
• does not survive in environment

Epidemiology

• main vector/reservoir hosts are carnivora
• Canidae (dogs, foxes, jackals, wolves)
• Mustelidae (skunks, weasels, badgers)
• Chiloptera (bats)

• two cycles recognised
• urban
• sylvatic

• urban
• transmission sustained in domestic dogs
• usually in countries with poor or no veterinary control efforts, e.g. Asia; in India 18,000 people each year die from urban rabies
• virtually nonexistent in North America, Western Europe, as there is adequate dog control and vaccination programmes

• sylvatic
• on increase, e.g. current epidemic in Europe involving red foxes and the disease is spreading 60 km/year
• appears to be impossible to contain despite fox control measures as foxes not killed will enlarge their territory
• recent attempts at mass vaccination of foxes show promise
• if bats infected usually little cross infection with terrestrial mammals

Differential Diagnoses

     1.  canine distemper, hepatitis
     2.  pseudorabies
     3.  bacterial parasitic and mycotic infections of CNS
     4.  poisons - lead, alkaloids, 1080, OPs, etc.
     5.  trauma
     6.  foreign body in oropharynx
     7.  equine leucoencephalomalacia