B206 - EQUINE INFLUENZA

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B206 - EQUINE INFLUENZA

Nature of the disease
Equine influenza is an acute, contagious respiratory disease. It is caused by two distinct subtypes of influenza A viruses within the genus Influenzavirus A of the family Orthomyxoviridae: subtype 1: H7N7 and subtype 2: H3N8. 
Classification
OIE, List B disease
Susceptible species
Horses, other equines, man
Distribution
The disease occurs worldwide except in the Pacific Region where it has never been reported.
Clinical signs 
Short period of incubation of 2-3 days.
  • Fever
  • Dry cough moving to a moist cough
  • Tiredness, anorexia,
  • Watery nasal discharge, only sometimes,
  • Secondary infection of the upper respiratory tract that can be fatal in foals
Post-mortem findings 
Bronchiolitis with abundant bilateral serous discharge.
Differential diagnosis 
Specimens required for diagnosis 
For virus isolation it is important to obtain samples as soon as possible after the onset of clinical signs. Samples include nasopharyngeal swabs or nasal washings. Swabs should be transferred to a vial containing transport medium immediately after use (see OIE documentation) if samples are kept more than 2 days before inoculation they should be frozen at -60°C or below. Isolation involve successive passages on cultivated embryonic cells and can only be done in advanced laboratories. Alternatively antigens can e detected by ELISA.

Serology must be done on paired sera, spaced by two weeks and should be submitted at the same time in the same laboratory.

Transmission   
The disease is extremely contagious and the disease appears in epidemics. It can be spread direct contact, aerosol from coughing (up to 30m), wind (up to 8km) and indirect contact with infected material during 36 hours. There is no chronic carriers
Risk of introduction   
Equine influenza could be introduced by importation of infected horses. However there is no chronic carriers and incubation is short so it is likely that disease would be recognised at quarantine inspection.
Control / vaccines  
Influenza vaccines are widely available and are routinely used in competition horses in Europe, the Americas, and Asia. In free countries vaccination should remain prohibited except for sport horses participating to international races.
References
  • Equine Influenza, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 1084-1085
  • Equine Influenza, In Veterinary Medicine, Saunders, Eight ed, 1997, London p. 104-1044
  • GEERING WA, FORMAN AJ, NUNN MJ, Equine Influenza In Exotic Diseases of Animals, Aust Gov Publishing Service, Canberra, 1995, p 96-100
  • Office International des Epizooties, 2002