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Understanding Rain Rot

Jan 30, 2014

While spending as much time as possible at pasture can be good mentally for your horse, if you live in an area with wet or very humid conditions, your horse might be at risk of contracting a bacterial skin disease commonly known as "rain rot."

Ann Swinker, PhD, an extension horse specialist at Penn State University, explains what the infection looks like, how to treat infected horses, and ways to prevent horses from getting or spreading the infection.

Cause

"Rain rot or rain scald (also known as dermatophilosis) is caused by bacterial infection, and it often is mistaken for a fungal disease," Swinker says. "The bacteria live in the outer layer of skin and cause from pinpoint to large, crusty scabs."

Dermatophilus congolensis, the bacterium found to cause this infection, lives in dormant within the skin until the skin is compromised in some way, which can happen when there's prolonged wetness, high humidity, high temperature, or attacks by biting insects, according to The Merck Veterinary Manual. Warm temperatures and high humidity can also cause an increase in the number of biting insects (particularly flies and ticks) present that can spread the infection from horse to horse.

Rain rot occurs when the infective zoospores (created by D. congolensis bacteria to propagate themselves) reach a compromised skin site. Swinker says, "The zoospores germinate and produce hyphae (threadlike tentacles), which penetrate into the living epidermis and spread in all directions, resulting in an acute inflammatory skin condition."
 
Source: TheHorse