Equine Influenza (EI)
is a highly contagious though rarely fatal respiratory disease of
horses, donkeys and mules and other equidae.
The disease has been
recorded throughout history, and when horses were the main draft
animals, outbreaks of EI crippled the economy.
still have a severe impact on the horse industry.
EI is caused by two
subtypes of infl uenza A viruses: H7N7 and H3N8,
of the family Orthomyxoviridae.
They are related to
but distinct from the viruses that cause human and avian infl uenza.
Equine Infl uenza is a disease listed in the OIE Terrestrial Animal
Health Code and countries are obligated to report the occurrence of
the disease according to the OIE Code.
The disease is
entrenched in most of the world, with the exceptions of Australia
(where an important outbreak occurred in 2007), New Zealand, and
How is the disease
transmitted and spread?
Highly contagious, EI
is spread by contact with infected animals, which in coughing excrete
In fact animals can
begin to excrete the virus as they develop a fever before showing
It can also be spread
by mechanical transmission of the virus on clothing, equipment,
brushes etc carried by people working with horses.
Once introduced into
an area with a susceptible population, the disease, with an
incubation period of only one to three days, spreads quickly and is
capable of causing explosive outbreaks.
transportation are factors that favour the spread of EI.
In fully susceptible
animals, clinical signs include fever and a harsh dry cough followed
by a nasal discharge. Depression, loss of appetite, muscle pain and
weakness are frequently observed. The clinical signs generally abate
within a few days, but complications due to secondary infections are
common. While most animals recover in two weeks, the cough may
continue longer and it may take as much as six months for some horses
to regain their full ability. If animals are not rested adequately,
the clinical course is prolonged.
practiced in most countries. However, due to the variability of the
strains of virus in circulation, and the diffi culty in matching the
vaccine strain to the strains of virus in circulation, vaccination
does not always prevent infection although it can reduce the severity
of the disease and speed recovery times.
The OIE also
convenes an Expert Surveillance Panel on Equine Infl uenza Vaccine
that examines the strains of virus in circulation making
recommendations on which strains should be included in the vaccines.