Equine Influenza (EIV)

Disease Overview

Equine influenza virus (EIV) is one of the most common and contagious infectious upper respiratory diseases in horses. Endemic in the United States equine population, EIV spreads rapidly, with clinical signs appearing 24 to 72 hours after exposure. A coughing horse can propel equine influenza virus more than 50 yards and shed virus for seven to 10 days following infection. The virus causes damage to the lining of the trachea so rest during the recovery period is beneficial to avoid secondary pneumonia.

Merck Animal Health Solutions

Transmission Parasite Life Cycle

EIV spreads directly in aerosolized droplets dispersed by coughing or direct contact (nose-to-nose). It spreads indirectly through fomite transmission—hands, clothing, vehicles and trailers, stalls, and common-use articles such as brushes, buckets and bits can all spread EIV.

Clinical Signs

Infection affects the central nervous system.

Fever (>101.5° F)
Edema
Enlarged lymph nodes
Frequent dry cough
Nasal discharge
Lethargy
Lack of appetite
Possible secondary bacterial pneumonia

Risk Factors

Travel
Contact with other horses, especially in large numbers
Exposure to horses that have traveled
Compromised or immature immune system
Equine flu season typically peaks from December to April but disease can occur any time of year

References

Infectious Upper Respiratory Disease Surveillance Program. Merck Animal Health and University of California, Davis, School of Veterinary Medicine (Nicola Pusterla). Ongoing research 2008-present.