Equine influenza is a viral respiratory disease of horses caused by influenza A viruses. There are two main strains that cause the disease: Equine-1 (H7N7) and Equine-2 (H3N8). The disease was first described in the 4th century CE and outbreaks have occurred globally throughout history. Clinical signs include fever, nasal discharge, cough, depression, and reluctance to eat or drink. Diagnosis involves isolating the virus from nasopharyngeal swabs or observing the rapid onset of clinical signs. Prevention focuses on vaccination and hygiene procedures while infected horses require rest and supportive care with NSAIDs or antibiotics.

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Synonymous:
 Horse flu
 A-1 influenza
Etiology:
It is a viral disease
Family-----Orthomyxoviridae
Genus-------Orthomyxovirus
Species------ Orhtomyxovirus-A
Equine influenza (horse flu) is the disease caused by strains of influenza-A that
are enzootic in horse species. Equine influenza occurs globally, and is caused by two main
strains of virus:
o Equine-1 (H7N7)
o Equine-2 (H3N8)
History:
 It was noted as far back as Hippocrates (father of medicine)
 Greek veterinarian in 330 C.E (Common Era) described the disease in horse population
 In Europe, next case was reported in 1299
 Outbreak in North America 1872;
o This outbreak is known as “Most destructive recorded episode of the E.I in history”
o First time defined it as; "An epizootic specific fever of a very debilitating type, with
inflammation of the respiratory mucous membrane, and less frequently of other
organs, having an average duration of ten 10-15 days, and not conferring immunity
from a second attack in subsequent epizootics."
 Australia had remained EI free until an outbreak in 2007, but they controlled it & regain
the EI free status.
Note: Swine influenza was pandemic (outbreaks) in 1918, 1968-69 & 2009 due to high
transmission, no immunity & high number of host.
Equine Influenza is characterized by very high number of transmission in horses & have a
relatively short incubation period of 1-5 days usually. Horses of 1-5 year old are most
susceptible.
H = Hemagglutinin N = Neuraminidase
H = 1-9 N = 1-16 Total combinations of HN = 144
Avian Influenza = H5N1 Swine Influenza = H1N1

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Clinical signs:
Constant fever (106°F)
Flu (serous nasal discharge)
Running nose
Dry cough
Depression
Reluctant to eat & drink for several days
Clinical signs usually last for < 3 days in uncomplicated cases. They usually recover in 2-3 week
Diagnosis:
 Isolation of virus & HI  Sample: Nasopharyngeal swabs
 Rapid onset of the clinical signs
Treatment:
 NSAIDs for fever >104°F
 Antibiotics if fever persists beyond 3-4 days & pneumonia or nasal discharge too.
 Rest for 3 weeks is also recommended
Prevention:
 Prevention of equine influenza outbreaks are maintained through vaccines and hygiene
procedures
 Countries that are equine influenza-free normally impose strict and rigorous quarantine
measures
 There are two types of vaccines available: Live & Inactivated
 Vaccine schedule generally requires a primary course of vaccines followed by booster
shots.
 The UK requires horses participating in show events be vaccinated against equine flu,
and this vaccination is repeated at every 6 months