Equine Influenza - Pedigogy

Master Preventive Medicine – Notes, Case Studies and Practical Insights – with Lomash

Equine Influenza:

Syn: Equine distemper, Pink eye, Catarrhal fever

It is acute, febrile highly contagious disease of horse
It is characterized by general septicemia, respiratory problem accompanied by severe persistent dry cough.
Horse, mule and donkey are susceptible. Horses of age 2-6 months are most susceptible.

Etiology:

It is caused by two distinct sub-types of Influenza A virus within genus influenza A of family Orthomyxoviridae
2 sub-types; A₁(H₇N₇), A₂ (H₃N₈)
H₇N₇ is thought to be extinct, and the current H₃N₈ has spread widely throughout the world.
They are related to but distinct from the viruses that cause human and avian influenza.

Epidemiology:

Outbreaks in susceptible horse populations are associated with considerable economic impacts. China, Japan, and Australia experienced devastating epidemics of equine influenza affecting tens of thousands of horses in 2007.
Equine influenza (Orthomyxovirus) A/equine type-2 H3N8 was first recognized in 1963 and has subsequently become endemic in many countries.
New Zealand and Iceland are currently free of equine influenza.
Antigenic divergence of equine influenza virus (EIV) over time has resulted in the emergence of distinct lineages (European and American).
Since 2010, the Florida H3N8 clades 1 and 2 sublineage strains (from American lineage) have predominated in EIV outbreaks worldwide.
A carrier state is not recognized for equine influenza.
From july 2022-September 2024, sporadic outbreaks have been reported in Belgium, UK, France, Germany, Ireland, Netherland and Sweden.

Transmission:

It is transmitted through droplet infection.
Indirect transmission via fomites (clothing, hands, shared water) should also be considered an important mechanism of disease transmission.
Shedding is longest in naive horses and lasts ~7–10 days after the time of infection.
Close contact with infected animal.

Pathogenesis:

Clinical Signs:

Incubation period of disease is 2-3 days
High rise of temperature; 103-106°F
Watery to mucopurulent discharge from nostrils
Cough (dry, harsh, and nonproductive), pneumonia
Distressed abdominal respiration
Inappetance, muscular weakness
Animals disincline to move and have stiffy gait
Cervical lymph glands are painful
Pneumonia and edema of lungs may develop
Vasculitis and distal limb edema, myositis, and myocarditis can occur as infrequent complications of EIV infection.
Clinical signs are generally more severe in younger horses (1–5 years). Mildly affected horses demonstrate complete and uneventful recovery in 2–3 weeks.

Diagnosis:

Based on clinical findings
Based on PM findings
- Lesion in bronchi characterized by signs of bronchiolitis
- Changes seen in URT
Isolation of virus from nasal swab in chicken embryo
Hemagglutination-inhibition test (HI)
Complement fixation test
Serum neutralization test
ELISA, PCR

Differential Diagnosis:

Treatment and Control:

There is no specific treatment against this viral disease.
Symptomatic treatment with broad-spectrum antibiotics and sulphonamides to prevent secondary bacterial infection
Supportive therapy with antipyretics, antihistamine, sedatives, expectorants, bronchodilators and liniment massage for 5-7 days.
Strict hygiene measures are main key to prevent spread of infection.
Transporting vehicles should be thoroughly disinfected before loading and following unloading of animal.
Sick horses should be isolated following standard biosecurity guidelines for 21 days after resolution signs in last newly infected horse.
Vaccination of horse if available at 6-12 months of age for 2 occasion. Booster dose given every 6 months.
Most influenza vaccines are inactivated, adjuvanted vaccines recommended primarily for intramuscular administration.