Pseudorabies (Aujeszky Disease)

Pseudorabies (Aujeszky Disease) also known as Mad itch and infectious balbar paralysis.

Pseudorabies (Aujeszky Disease) is an acute fatal disease of swine and other domestic and wild animals are affected incidentally.

Etiology

• Pseudorabies (Aujeszky Disease) is caused by porcine herpes virus-1, (Pseudorabies virus, a member of the family herpes viridae, subfamily alphaherpesvirinae.
• It is a DNA virus contains only one serotype.
• The virus is inactivated at 5.25% sodium hypochlorite.

Epidemiology

• The disease is worldwide in distribution.
• All age group of pigs are affected.
• Young animal are highly susceptible than adult.
• Morbidity rate: 100% and Mortality rate: 50% in young piglet.
• Economic loss may reach 100% in piglets less than 7 days old.

Transmission

• Nose to nose or  oro-nasal contact.
• Indirect transmission commonly occur through inhalation of aerosol.
• Rodents act as reservoir for virus.

Pathogenesis

Clinical manifestation

The major systems affected in this disease are respiratory, nervous and reproductive system. Piglets less than one month old are more susceptible and died due to encephalitis.

The symptoms include:

• Fever  (Temp.107^oC) occurs prior to the onset of nervous signs.
• Inco-ordination of hind limbs followed by recumbency.
• Muscle tremor.
• Paddling movement.
• Lateral deviation of head, frothing at the mouth.
• Nystagmus.
• Convulsion (epileptic form seizure).
• Snoring respiration.
• Vomition and diarrhoea in some affected animals.
• Death occur 12 hrs after onset of first signs.

Grower and adult pig

• Respiratory signs are common.
• Fever, sneezing, nasal discharge, coughing and severe dyspnoea.
• Trembling, incoordination, paralysis and convulsion precede with death.
• Infection in early pregnancy causes early embryonic mortality and abundant vaginal discharge.
• Infection in late pregnancy may result in abortion, birth of mummified foetuses.

Cattle

• Local pruritis with violent licking, chewing and rubbing of the part until great tissue destruction  so, it is called as mad itch.
• Itching is localized to any part of the body, but most common on head, flank and feet.
• Intense excitement, convulsions and constant bellowing, salivation and respiratory distress and ataxia.
• Manical behaviour, circling, opisthotonus and paralysis.

Sheep

• Outbreak in sheep is associated with skin abrasions, acquired through shearing.
• Fever.
• Nibbling of their fleece and frenzied attempt to bite on the skin and rub it against  the wall  and bar of their pen.

Goat

• Rapid death.
• Unrest.
• Frequently lying down and rising up.
• Crying, profuse sweating.
• Paralysis.
• No pruritis.

Dog and cat

• Clinical sign is similar to that of cattle.
•  Death is eminent within 2 days following manifestation of clinical signs.

Necropsy Finding

• Lungs show congestion, edema and some haemorrhage.
• Splenomegaly.
• Meninigitis.
• Necrotic lesion with inclusion body formation in upper respiratory tract and lung is suggestive of pseuorabies in pig.
•  In aborted foetus or very young piglets- white spot on liver is pathognomic lesion.

Sample collection

• Live animals- oropharyngeal fluid, nasal and tonsil swab, paired sera sample.
• Dead animal -lung, brain and tonsil from pig and spinal cord from cattle.

Diagnosis

• Based on clinical signs and lesion.
•  Isolation and identification of the virus made by inoculation of tissue homogenate (tonsil and brain)  into a susceptible cell line such as porcine kidney (PK-15) or SK6, or primary or secondary kidney cell.
• The specificity of the cytopathic effect is verified by immunofluorescence, immunoperoxidase or neutralisation with specific antiserum.
• Detection of viral antigen by PCR.
• Detection of antibodies in serum by VNT and ELISA.

Differential diagnosis

• Rabies
• Streptococcal meningitis
• Encephalopathy
• Salt poisoning
• Reproductive inefficiency associated with  enterovirus (SMEDI) and parvovirus infections.
• Polyencephalomalacia

Prevention and control

• The disease may be controlled by vaccination of piglets at 9-12 weeks of age with either modified live or inactivate vaccine.
• Recombinant  DNA derived, gene -deleted  Marker vaccines(Lack of specific glycoprotein gG, gE, or gC) are available to differentiate vaccinated from infected animal.
• Depopulation and  repopulation of swine  is practiced, when prevalence of infection above 50%.
• The premises are cleaned, disinfected and left empty of pigs for 30 days.
• Test and removal of pigs.
• Due to low incidence of disease no vaccines are available in India.