I’m hearing about more cases of equine flu. Why are more horses being infected?

By Duane E. Chappell, DVM, Merck Animal Health

Simply put, the equine influenza virus is evolving. Just like human flu, equine flu changes but at a much slower rate. Through the Merck Animal Health Equine Respiratory Biosurveillance Program, researchers found that horses involved in a 2013 influenza outbreak were infected with a new flu strain named Florida ’13.1

To reach this conclusion, researchers compared various equine influenza vaccine strains, revealing that the Florida ’13 strain differed significantly from older strains including Ohio ’03 and Kentucky ’97. Ongoing research through the Equine Respiratory Biosurveillance Program at the time of this article shows Florida ’13 is the vaccine strain closest to today’s equine influenza virus.2

In response to these findings, Merck Animal Health updated the PRESTIGE® influenza vaccines to account for the Florida ’13 strain. PRESTIGE® vaccines are the only vaccines available that contain the Florida ’13 vaccine strain.

Importance of updated vaccines

The equine influenza virus infects horses by binding to respiratory cells, and vaccines work by producing antibodies that bind to key sites on the virus, preventing cell infection. Mutations in an influenza virus decrease a vaccine’s ability to bind to these key sites, leading to reduction in or a total lack of protection.

Work with your veterinarian to determine the right time to protect your horses with an updated vaccine that includes Florida ’13. You can also implement a few straightforward biosecurity measures to help reduce horses’ risk of influenza.

Remember that even horses that don’t travel are still susceptible to equine flu, especially if they live at a barn with other horses coming and going.

To help protect time in the saddle—and most importantly, horses—remember these main points:

• The EIV virus is changing.

• Not all vaccines are created equally.

• Biosecurity measures help reduce horses’ risk (see examples on page 4).

Watch this video to see how a changing virus affects vaccination effectiveness.