Life cycle of Muscid fly


Summer Sores

Summer sores are a common problem in Arizona. These sores are commonly found on the lower limb, corner of the eye, and the urethral process of geldings and stallions. They can also be found on the face neck or any other area of the body that has had an open sore or wound. They are characterized by a non-healing sore with small yellow granules, and decayed tissue. Summer sores are caused by three nematodes most commonly named are Habronema muscae, Habronema majus and Draschia megastoma.

The adult worms live in your horse’s stomach. The eggs are passed into manure where flies ingest them. The larvae then move to the mouthparts of the flies and get deposited on moist areas of your horse while the flies are feeding. The routine life cycle occurs when the fly lands on the horse’s mouth, the larvae are deposited and swallowed.

Flies are attracted to different areas on the horse for feeding, mouth, eyes, wounds and sheath. Any skin abrasions wounds are also potential sites for the larvae to set up housekeeping. The larvae do some damage directly simply by migrating into tissues and causing irritation. The larvae cannot live in these areas. Much of the reaction is from the horse’s own immune system responding to the larval invaders.

Habronemiasis involving the eye generally has lesions on the conjunctiva (pink tissues around the eyeball), on the third eyelid itself or on the eyelids. The first sign horse owners notice is ulcerations, especially in the corner of the eye. Your horse will rub their eye and increase the damage. Applying corticosteroid ointment may help reduce the reactivity for small and fairly fresh lesions. Frequently, the habronema granules need to be removed.

Preventing habronemiasis around the eyes means strict fly control. A properly fitted fly mask can be ideal. If your horse won’t tolerate a fly mask, consider the “roll on” fly repellants around the eyes. These will need to be applied at least once a day.

On the skin, habronemiasis may need to be differentiated from cancerous growths, proud flesh and or wounds. A surgical biopsy will differentiate between cancerous growths and habronemiasis. Occasionally a skin scrape of the area may reveal the calcified larvae when examined visually or microscopically.

Obviously fly control is the best way to prevent habronemiasis on the skin as well as around the eyes. Use of fly sprays, fly repellants and environmental modifications can all help. Be sure to put fly spray around your male horses’ prepuces. It is important to make sure any open wounds are covered to prevent fly damage and larval deposition. The sores found on the skin may respond to symptomatic treatment such as corticosteroid ointments, antibiotic ointments and cleaning. Systemic steroids and anti-inflammatory medications may help. Many end up requiring surgical removal or cauterization to kill the larvae and halt the granulation buildup.

Deworming your horse with ivermectin or moxidectin will treat the parasites in your horse; however, the larvae can be transferred from an infected horse to another via the flies. Habronemiasis is commonly a yearly battle for some horses. Contact Arizona Equine today to treat your horse and address any parasites.

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