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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.
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Classification
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OIE, List B disease
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Susceptible species
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Horses, other equines, man
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Distribution
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The disease occurs worldwide except in the Pacific Region where it has never
been reported.
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Clinical signs
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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
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Post-mortem findings
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Bronchiolitis with abundant
bilateral serous discharge.
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Differential diagnosis
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Specimens required for diagnosis
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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.
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Transmission |
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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
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Risk of introduction |
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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.
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Control / vaccines
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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.
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| References
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- 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
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