What are Summer Sores?
The larvae of Habronema or Draschia worms usually live on the inside of the equine stomach wall and do not migrate internally. Most horses infested with these worms show very minimal signs, unless the infestation is extremely heavy. Then the stomach can become irritated or it can perforate and rupture. When these worms are deposited on the skin an unusual life cycle begins as the larvae are unable to mature into adult worms. The larvae cause severe local inflammation and can rapidly grow into large, painful lesions.
In some cases the larvae can infiltrate the gastrointestinal system, causing gastric inflammation or ulcers. The larvae can also migrate up through the nose and into the lungs. They will form cysts if there is a large number of larvae present in the lungs.
Summer sores in horses can occur any time of year, but during warm months they tend to become more prevalent. This is because biting insects are at their peak and they tend to leave the larvae of stomach worms in the bite wounds that they make. Moist areas of the body such as the eyes, lips, ears, penis, and urethra are at much higher risk of developing summer sores. Other areas of the body that are prone to scrapes or irritation are also prone to summer sores.
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Symptoms of Summer Sores in Horses
Summer sores can become quite large and become very painful for your horse. It is important to check your horse over thoroughly for any signs of the beginning of summer sores. During the warm months, you may want to check your horse daily or every other day. If you see any of these symptoms, be sure to contact your veterinarian for treatment as soon as possible.
- Open lesions that attract flies
- Lesions that look greasy
- Blood tinged fluid draining from lesions
- Lesions that have yellow or white calcified material, resembling grains of rice
- Lesions that enlarge and spread slowly
- Hard nodules or red or brown tissue that is raised
- Nodules around the eyes, mouth or penis
Causes of Summer Sores in Horses
Summer sores are more prevalent during the warm months, when biting insects are most active. The larvae of Habronema and Draschia are deposited in any open wounds on your horse’s skin. The larvae begin to cause inflammation and pus begins to build in the wound. As the wound festers and becomes moist with pus, more flies are attracted to the area causing extreme irritation.
Diagnosis of Summer Sores in Horses
Your veterinarian can most times diagnosis summer sores based on the symptoms that are present. However, another condition called proud flesh, or proliferative granulation tissue, can present with similar symptoms.
The presence of lesions containing pus and calcified material will help point your veterinarian in the right direction. But, to make a definitive diagnosis, a sample of the pus and calcified material will need to be collected. A skin scraping may also be collected to look for the larvae that cause summer sores. Once summer sores have been diagnosed, your veterinarian will set up a treatment plan that kills the parasites and treats the lesions.
Treatment of Summer Sores in Horses
Your veterinarian will give you a treatment plan that is aimed at treating the current lesions as well as killing the larvae that present. Controlling the flies that are around your horse will also be essential to curing summer sores.
Treating the lesions will usually require a topical ointment that is a glucocorticoid, a powerful anti-inflammatory medication. Some instances may require a topical ointment mixture of a glucocorticoid and dimethyl sulfoxide or DMSO. The main goal is to reduce the inflammation to slow the progression of the lesions.
Many times the ointment alone will not heal the summer sores. In these instances, the tissue needs to be surgically shaved or frozen off for full healing to take place. If a secondary infection has begun, a broad spectrum antibiotic will be necessary to clear the infection.
The larvae need to be treated systemically with moxidectin or ivermectin. This will remove the adult worms from the stomach lining. In some cases, the medications are directly applied to the lesions to kill the larvae.
Open lesions draw flies and flies will irritate the lesions and could possibly put more larvae into the wound. The use of a fly repellent ointment and fly masks will help keep flies away, but a repellent that controls flies throughout your farm or stable is more effective.
Recovery of Summer Sores in Horses
Summer sores can be treated and healed; though horses that experience large lesions do recover with some scarring. The best way to control summer sores is to prevent them. Speak with your veterinarian about starting a strict de-worming program for your horse. Keep fly control as your top priority throughout the warm months to keep all biting insects away from your horse.