Research has shown that the reservoir for the bacteria that causes pigeon fever is the soil. Flies then transmit the bacteria from horse to horse.

Five cases of pigeon fever reported in Washington State

This bacterial infection, spread by stable, horn and houseflies, is becoming more common as weather conditions change.

Strangles can be passed from horse to horse by direct contact.

Two Washington State farms quarantined due to equine influenza virus

The highly contagious viral disease is spread via airborne droplets exhaled by infected horses or contact with contaminated surfaces.