Exotic Diseases

CNS Diseases: Pseudorabies (Aujeszky's Disease)

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Species Affected

pigs - main species

also rodents, cattle, sheep, cats, dogs, horses

Clinical Signs

incubation 1 week
symptoms related to species/age affected

Pigs

(i) less than 2 weeks

very susceptible
indistinct syndrome
fever, convulsive episodes, prostration
100% mortality - within few hours of onset of symptoms

(ii) piglets - older

protracted course for up to a week
fever, anorexia
development of CNS signs
hindlimb incoordination
walk with sideways progression or circle
fine to coarse muscle tremors
lateral deviation of head
5-25% mortality
may get respiratory symptoms
dyspnoea, nasal discharge

(iii) adults

symptoms vary with strain of virus
evidence for increasing virulence

if mild

anorexia, dullness, constipation

may get abortion/mummification/stillbirths

if disease caused by more virulent strains

get a spectrum of signs - from mild incoordination to fever, vomition

respiratory symptoms

sneezing/nasal discharge

coughing/severe dyspnoea

development of incoordination, paralysis and mortality

Cattle, Sheep, Cats, Dogs

sudden death
intense local pruritis is the cardinal sign
nibbing, biting, leading to self mutilation
excitement

convulsions
bellowing/howling

paralysis

salivation
respiratory distress/cardiac irregularities

invariably fatal

death within 24 hours dogs - more rapid in cats
death between 6-48 hours cattle

Lesions

in pigs - tonsillitis, rhinitis and pharyngitis

pulmonary congestion, consolidation

other species lesions referable to self trauma
histopathology: severe nonsuppurative encephalomyelitis/neuronal degeneration
may find intranuclear inclusion bodies (Cowdry type A) in both the necrotising lesions of upper respiratory tract, lungs and brain

Aetiology

Herpesviridae
broadest host range of the animal herpesviruses
relatively thermostable, resistant to pH
can survive in environment up to 2-7 weeks or in infected meat 5 weeks
one serotype, but variations of virulence between strains

Pathogenesis

portals of entry

nasal, oral epithelium

early multiplication in upper respiratory tract
may be a short, ill defined viraemia
spread to brain is via cranial nerves or other peripheral nerves

gives rise to pruritis etc.

viral excretion primarily from nose and mouth for up to 17 days post infection

Epidemiology

pigs main reservoirs (rats probably minor)
infection of other species originates from these 2 species; no infection of other cattle from affected cattle occurs
viral excretion for up to 17 days; primary spread airborne

virus also excreted in milk
virus may be transmitted by boars at service
transplacental infection can also occur

carriers occur - especially in adults and vaccinated animals

these may represent main vehicle for spread

latent infection occurs and may be activated by stress, such as transport, dietary change, farrowing (c.f. Herpes simplex)

Differential Diagnosis

for pigs
     1. porcine polioencephalomyelitis (Talfon-teschen disease)
     2. swine fever
     3. haemagglutinating encephalitis virus
     4. generalised inclusion body rhinitis
     5. streptococcal meningoencephalitis
     6. hypoglycaemia
     7. salt poisoning
     8. arsenic/mercury poisoning

other species - disease distinctive but could be confused with rabies


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