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What is Fly Bite Allergy?

Biting flies are a huge pest to horses.  Add an allergy to the fly saliva and the result is severe discomfort and annoyance.  Horses with a fly bite allergy experience a type of allergic reaction after the saliva enters their skin.  The symptoms can vary but usually lesions appear, and pruritus, and hair loss develop in a relatively short time.  There are many species of flies that can bite your horse; he may be sensitive to one or a multiple of them.  Your veterinarian will likely be able to diagnose your horse’s condition by physical exam alone but may prefer to run some diagnostics to verify.  Once properly diagnosed, treatment is fairly straight forward and prognosis of recovery is good.

If your horse is allergic to flies and he sustains one or more bites, he may display severe discomfort.  While it is not a medical emergency, you should contact your veterinarian to ease his discomfort and discuss what steps to take next.

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Symptoms of Fly Bite Allergy in Horses

Symptoms of a fly bite allergy may include:

  • Small lumps
  • Pruritus
  • Alopecia 
  • Lesions
  • With or without crusted papules
  • Serum may ooze from the lesions
  • Thickening of the skin
  • Rat tail/ roached main 

Often the symptoms appear on the areas listed below but they can occur anywhere on your horse’s body:

  • Neck
  • Flank
  • Tail
  • Rump

Types

There are many species of flies that can cause a reaction in your horse.  There is the black fly, stable fly, horse fly, stable fly, and more. Depending the season and the region you live in, the fly species can vary.  However, no matter the species of the fly, allergies to a fly bite are typically the same.  You may notice in the cold seasons that the condition regresses.

Causes of Fly Bite Allergy in Horses

Insect bite hypersensitivity can also be known as summer itch or sweet itch.  It is actually an allergic reaction to the saliva of the biting fly; it is considered a systemic Type 1 allergic reaction.  When the fly bites your horse, it causes the mast cells to release histamine causing intense itching which in turn causes the horse to scratch constantly.  This causes open sores and possibly a secondary bacterial infection.

Diagnosis of Fly Bite Allergy in Horses

The reason most owners call their veterinarian is not because they see the lesions on their horse but because of the level of discomfort the horse is experiencing.  During her diagnostic process, the veterinarian will complete a full physical exam on your horse.  Not only will she make note of all his symptoms of discomfort but also any other symptoms he is experiencing.  By examining him, she can feel for lesions and evaluate his skin everywhere.  She will also note the appearance of his mane and tail which can be helpful in her diagnosis.  She may want to clip and clean some areas in order to better evaluate the skin.

In cases where the veterinarian is unsure of the cause of your horse’s lesions, she may want to collect a skin sample for biopsy testing.  With testing, she can determine if it is a malignant tumor or lesion or if it is benign.  For those with bug bite allergies, the specimen is usually composed mainly of eosinophils with lymphocytes.  The biopsy may also reveal a secondary bacterial infection occurring in and on the skin. 

In addition to this, she may collect a serum sample to measure the immunoglobulin E concentration against various insect allergies.  If there is an appropriate test available, it can be helpful in identifying which species is actually causing your horse’s symptoms.

Treatment of Fly Bite Allergy in Horses

The veterinarian will need to treat your horse’s system as a whole in addition to the individual lesions.  She may prescribe antihistamines and/or a steroid to calm your horse’s systemic response down. She will also treat the lesions with topical medications in a spray or ointment form.  She may need to prescribe oral antibiotics or give an injection to take care of any secondary bacterial skin infection.

You can utilize natural herbal treatments if desired.  You can make a paste out of baking soda and water and apply it to the bite.  It will draw out the toxin and relieves the itch quickly.  You can also use natural ingredient lotions to relieve the itching and encourage tissue healing.  

Some veterinarians recommend you try allergy testing your horse.  If he comes back with a high sensitivity to fly saliva, you may be able to try allergy shots.  The purpose of the shot is to slowly desensitize your horse to the fly saliva so if he gets bitten, he will not have a severe response.  You will need to discuss this with your veterinarian if she thinks it is a viable option for your horse.  Some veterinarians do not believe the efficacy of these shots for horses.

Prevention of the fly bites is the most ideal treatment option.  There are fly sprays you can utilize to decrease the amount of flies your horse attracts.  You can also add screens or mesh netting to your stall windows to decrease the amount of access points for insects.  In addition to these things, you can install fans to prevent the flies from being able to land easily on your horse.  If they cannot land, then they cannot bite.

Recovery of Fly Bite Allergy in Horses

The more bites your horse receives, the more severe his reaction will become.  However, if you are able to prevent the bites from continuing, you will help your horse recover more quickly than if the biting continues to occur.  As long as you heal the lesions and bacterial skin infection if present, your horse’s prognosis of recovery is good.