Thrush is caused by which organism?

• A. Fusobacterium necrophorum
• B. Streptococcus equi
• C. Escherichia coli
• D. Staphylococcus aureus

Answer: (A)

Thrush is a bacterial infection of the frog of a horse’s hoof. It is most commonly caused by Fusobacterium necrophorum, an anaerobic bacterium that is part of normal flora but proliferates in moist, dirty hoof conditions. Infected frogs develop a foul odor and necrotic, black tissue in the frog sulci, and the condition worsens with damp environments and poor hoof hygiene. The other organisms listed are linked to different diseases or infections in horses (for example, Streptococcus equi with strangles), so they’re not the typical culprits behind thrush. Fusobacterium necrophorum is the organism most commonly associated with thrush.