Page 63 - July2021

Treatment for a hypersensitive reaction gener- ally includes antihistamines and steroids.
A horse with a summer sore on the penile sheath may spray urine instead of produc- ing a normal stream because the lesion is obstructing normal flow. A summer sore
on the legs may grow quite large, interfer- ing with use of the horse until the wound is treated or until the lesion regresses.
TREATMENT AND CONTROL
It is important to take proper care of wounds, so they stay clean and keep flies away from them. A standard treatment is to admin- ister a deworming drug containing ivermectin, two doses 3-6 weeks apart, to kill most of the worm larvae in the lesions. Horses that are routinely dewormed with ivermectin may not have problems with summer sores.
These sores were a common problem before the deworming agent ivermectin was introduced in the early 1980s in North America. Ivermectin, moxidectin and other drugs in their class turned out to be highly effective against the stomach worms whose larvae cause the sores, and wide- spread routine use of these drugs dramatically reduced the numbers of stomach worms - but they were not completely eliminated.
After the mid-1980s, summer sores became so rare that veterinarians who graduated after that time might never have seen this condition and might not recognize it, especially if their clients use ivermectin or moxidectin in their deworming programs. Summer sores are still uncommon, but the cases have increased in the last decade, possibly because some horses are not dewormed or because some of the worms are becoming resistant to ivermectin and related drugs. If your horse has a sore that won’t heal, the possibility of this condition should always be in the back of your mind.
The first step in dealing with the prob- lem is to have your veterinarian examine the skin lesion and make a diagnosis because certain other conditions can have similar signs. Summer sores can look like proud flesh, sarcoids, squamous cell carcinoma, mast cell tumors or pythiosis, aka swamp cancer which is caused by a fungus-like organism.
These tiny worms can also get into the horse’s eye since flies are often congregating around the eye to feed on secretions and might
cause signs similar to: onchocerciasis which is caused by the filarial worm Onchocerca that sometimes infects the eye; inflammation from a foreign object in the eye; or certain bacte- rial or fungal infections. Some of these eye problems are potentially more dangerous to the horse than a summer sore, so you need to consult your veterinarian.
The diagnosis is based on clinical signs. If it’s a skin lesion, it may require laboratory analysis of a scraping or biopsy. The biopsy sample may have to be from deep within the raw tissue.
To eliminate a summer sore your vet- erinarian may prescribe topical or systemic glucocorticoids, which are powerful anti- inflammatory drugs. Some veterinarians use a topical mixture of glucocorticoids/corticoste- roids and dimethyl sulfoxide (DMSO), which is also a good anti-inflammatory and has the advantage of readily penetrating deep into the tissue and taking the steroid with it.
Reducing inflammation should slow the proliferation of granulation tissue in the summer sore, but that alone may not be enough for heal- ing to begin, especially if the mass of abnormal tissue is very large. Sometimes the excess tissue has to be surgically reduced - shaved or frozen off - to remove the larvae that are still within
the tissue and to allow healing to take place. Antimicrobials drugs may also be needed to treat secondary infection, which is usually a result
of the horse biting, rubbing and itching the affected area. If not treated quickly and appro- priately, summer sores can persist for months and possibly require a costly surgical procedure to remove the granulated tissue and larvae.
Treating the horse systemically with ivermectin or moxidectin should remove the adults from the stomach. Sometimes these deworming drugs are applied directly to the sore as well, along with the anti-inflammatory treatments, to kill the larvae.
EQUINE HEALTH
“A standard treatment is to administer a deworming drug containing ivermectin, two doses 3-6 weeks apart, to kill most of the worm larvae in the lesions.”
Take proper care of wounds to keep flies from feeding on the secretions, such as those on a horse’s uncovered face.
A summer sore on the legs may grow quite large, interfering with use of the horse until the wound is treated or until the lesion regresses.
“If not treated quickly and appropriately, summer sores
can persist for months and possibly require a costly surgical procedure to remove the granulated tissue and larvae.”
SPEEDHORSE July 2021 61