Don't Let Summer Parasites Make Your Horse's Life Miserable

Gasterophilus intestinalis - Bot fly larvae raise havoc with horse's health.
Gasterophilus intestinalis - Bot fly larvae raise havoc with horse's health. Janet Graham

Newsdate: Monday, June 20, 2022 - 11:35 am
Location: GILROY, California

All horses are at risk from summer-loving parasites. Whatever your climate, wherever your horse resides - stalls, pastures, dry lots - these parasites thrive during summer months. See how they can infect your horse, the damage they do, and how to stop them.

Poster showing how threadworms - Onchocerca - attack horse's neck.

Poster showing how threadworms - Onchocerca - attack horse's neck

Whatever your climate, wherever your horse resides - stall, pasture or dry lot - many parasites thrive during the summer months.
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Bots (Gasterophilus): Female bot flies lay eggs on the horse’s hair. The eggs develop into larvae within five days of being deposited by the female . Larvae are stimulated to emerge by the horse licking or biting these developed eggs. The larvae either crawl to the mouth or are ingested.

Once inside the horse’s mouth they bury themselves in the tongue, gums, or lining of the mouth. During this stage, the horse may experience severe irritation, as well as the development of pus pockets and loosened teeth. Loss of appetite may also develop.

After approximately 28 days in the mouth, the larvae molt to the second stage and move into the stomach. The second and later third stage larvae typically attach to the lining of the stomach and the intestinal tract.

They cause irritation and may block the opening to the small intestine as well as interfere with digestion; chronic gastritis, ulcers, colic and other conditions can result.

Dewormers for Bots: ivermectin; moxidectin has limited control

Stomach worms (Habronema and Draschia): Responsible for producing “summer sores” or non-healing wounds and internal problems. Infection occurs when flies deposit infected larvae on the horse’s lips, nostrils, or open sores. When deposited in wounds, “summer sores” can occur. In large numbers, habronema can produce severe gastritis, and tumor-like enlargements may develop in the wall of thestomach. If they rupture, peritonitis usually ensues.

Dewormers for Stomach worms: ivermectin; moxidectin controls only adult stage of Habronema

Equine Threadworm (Onchocerca): Onchocerciasis is an infestation of the Onchocerca genus of roundworm, also referred to as neck threadworms.

These worms can be around 2.5 to almost 12 inches long in adulthood, and they generally live in the ligament that runs down the nape of the neck, although they have occasionally been found residing in other ligaments as well.

When the adult worms release their larvae into the system, they travel to the skin where they cause small, itchy bumps. On rare occasions they may also travel to the eye, causing swelling and pain.

When a gnat carrying onchocerca larvae bites a horse, the larvae migrate through the bloodstream where they mature and release microfilaria. The microfilariae then migrate to the skin.

Symptoms include small lumps on the chest, withers, neck, face, and belly; itching and rubbing, resulting in loss of hair and scaly skin; development of scabby, weeping sores; moon blindness and fistulous withers. The life cycle continues, as biting insects pick up the microfilariae from abraded lumps carrying infestation to other horses.

Dewormers for Threadworms: ivermectin

Don’t let these parasites interfere with your horse’s health this summer. Good News - Durvet’s Ivermectin Paste is very effective against each of these parasites. Important note: although fecal egg tests are a valuable tool in parasite control planning, they may not always indicate the presence of all parasite infestations.

Talk to your local veterinarian for detailed deworming recommendations.

FACT: Durvet’s Ivermectin Paste targets 34 parasite species and stages, including all 3 stages of the 2 most common bots.

About the Author

Flossie Sellers

Author picture

As an animal lover since childhood, Flossie was delighted when Mark, the CEO and developer of EquiMed asked her to join his team of contributors.

She enrolled in My Horse University at Michigan State and completed a number of courses in everything related to horse health, nutrition, diseases and conditions, medications, hoof and dental care, barn safety, and first aid.

Staying up-to-date on the latest developments in horse care and equine health is now a habit, and she enjoys sharing a wealth of information with horse owners everywhere.