Habronemiasis in Horses

There are three common nematodes, which can infect horses, the Habronema muscae, Habronema majus and Drashia megastoma.  Habronemiasis is also known as summer sores, jack sores and granular dermatitis.  Habronemiasis in horses is most common during the summer months in the southeastern United States.

There are parasitic microscopic worms called nematodes, which can live in a horse’s stomach.  The larvae of the nematodes move along the gastrointestinal tract intestines and pass out through the horse’s feces.  Horseflies then ingest the parasitic infected feces; the horsefly proceeds to feed on the horse and infects him with the nematode larvae.

Symptoms may include:

• Sores with pus
• Itching
• Non-healing lesions 
• Ulcers may bleed
• Growth of granulomas with small yellow granules
• Straining to urinate (sores on the penis)
• Skin is red and inflamed
• Colic

Types

• Conjunctival Habronemiasis - Nematode larvae infects the third eye
• Cutaneous Habronemiasis – Nematodes infects skin area (legs, penis, and any skin wounds)
• Gastric Habronemiasis – Masses grow in the stomach, caused by the nematode Draschia megastoma larvae; these masses can cause the stomach wall to rupture

Habronemiasis in horses is caused by the nematodes Habronema muscae, Habronema majus and Drashia megastoma. They are transmitted by:

• Feces left in pastures or stalls; lack of sanitation
• Infestation of horseflies
• Horse not being regularly dewormed

The veterinarian will go over the medical history of the horse. He may ask to see vaccination, dental and deworming records.  Let your veterinarian know if the stalls have had a recent infestation of horseflies. The veterinarian will then perform a full physical examination. The clinical signs of your horse, such as the presence of moist skin abrasions may point to habronemiasis. A skin scraping or biopsy may be required to confirm the condition.

A complete blood count and serum chemistry panel may be done to rule out underlying illnesses. The veterinarian will usually be able to diagnose habronemiasis by the physical examination, but the tissue biopsy will confirm the parasite.

Once habronemiasis is diagnosed the veterinarian will recommend a dewormer for your horse.   A common dewormer for horses is ivermectin. If the horse has a re-infestation, the veterinarian may then recommend moxidectin. Anti-inflammatory medication and corticosteroids may also be prescribed. Topical antibiotic ointment may be recommended to be applied to the lesions. In severe cases of habronemiasis, the veterinarian may suggest cryosurgery. Cryosurgery uses extreme freezing temperatures on the cells of the lesions.

Follow-up visits will be necessary to check on your horse’s progress.  The equine veterinarian will want to make sure the lesions that have been affecting your horse are healing properly, and that there are no more nematodes present.  Diagnostic tests may need to be retaken, such as a complete blood count (CBC) and a skin biopsy.  This will rule out bacterial infections and confirm that there are no more parasites. With eradication of the parasite, prognosis of a full recovery of habronemiasis is very good for your equine companion. It is important to avoid re-infestations of habronemiasis.  Prevention protocol may include:

• Daily removal of manure from stalls and pastures
• Daily grooming and inspection of your horse’s skin
• Daily checking of the body of your horse for any open wounds or sign of infection.
• Insecticides spray 
• Regular deworming of the horse
• Fly traps
• Fly baits
• Fans installed in the stalls
• Mesh screen installed in the stalls
• Horse fly masks must be used to protect your horse’s eyes
• Get rid of standing water 
• Feed should be kept in sealed containers
• Garbage should have tight fitting lids
• Natural oils such as lavender, pennyroyal, peppermint, and eucalyptus oil mixed with water can be sprayed on infested areas.
• Maintaining pastures, keeping them free of overgrown bushes and weeds

It is recommended, even if your horse appears healthy, that he be seen by an equine veterinarian once a year for a wellness check.  This will ensure that your horse is in good health.  Most conditions and diseases have a much better prognosis when they are diagnosed and treated in the early stages.