Page 104 - July 2022

VETERINARY VIEWS
“Summer is a time when insects thrive. Besides being annoying, some insects serve as vectors of disease.”
Ivermectin, and in some cases moxidectin, dewormer can rid your horse of parasites caused by flies.
INSECT-BORNE ILLNESS
STINGING INSECTS
Unless your horse runs into an active hive
or nest, stings from a bee, wasp, yellow jacket, hornet, or spider are usually singular. There
may be a localized reaction of swelling and pain at the site of the bite, or on occasion a mild allergic reaction may cause wheals (hives) to form. However, if a horse encounters a large population of stinging insects, multiple bites can create a serious allergic crisis that may progress to full-blown anaphylaxis. A swarm of stinging insects that attack the face and muzzle has the potential to cause enough airway swelling for the horse to be at risk of suffocation. Short of outrunning a troop of angry bees, there isn’t much you can do once you’re set upon other than to get out of there as fast as possible.
It’s always smart to get veterinary help immediately when a horse encounters stinging insects. You can poultice a single bite with a mixture of water and baking soda or apply some topical cortisone cream. During the wait for your vet or if you’re not close to veterinary help, you can give your horse an antihistamine (Benadryl) to slow the adverse reaction – consult with your veterinarian as to the appropriate dose.
Wasps and bees tend to build their nests in areas around barnyards or they may occur along trails you like to ride. In late spring, it’s a good idea to survey your property and buildings to check for nesting sites so you can eradicate them as early as possible. Wasp traps can be hung
in areas apart from where horses and humans congregate. Be aware that wasps and bees are attracted to sugary drinks (sodas, alcohol). Cleaning your barn and tack room of cobwebs also helps to reduce spider populations.
In late spring, it’s a good idea to check your property and buildings for wasp and bee nesting sites so you can eradicate them as early as possible.
Summer is a time when insects thrive. Besides being annoying, some insects serve
as vectors of disease. Viruses you may be most familiar with are equine encephalitis (Eastern and Western forms) and West Nile virus carried by mosquitoes. Fortunately, these diseases are well protected against with currently available vaccination products given annually before the start of insect season.
Flies are also culprits for passing disease. Equine infectious anemia (EIA, related to the human HIV virus) causes a chronic, wasting disease. Besides transfer from infected needles, large biting flies (deerflies or horseflies) can transmit this disease. Annual testing for EIA is a significantly important strategy to reduce this risk in horse populations. And it is important not to share blood-contaminated equipment between horses.
Parasites may be transferred by flies, as
well. Bot flies deposit their yellow eggs on a horse’s fur – once licked off and swallowed
by the horse, these develop into larvae within
the stomach. Black flies can transmit another parasite, Onchocerca cervicalis that migrates beneath the skin to cause hair loss. Onchocerca also can migrate into the eye, creating persistent eye inflammation or anterior uveitis (moon- blindness). Face flies can transmit eye worms (Thelazia). Another disease, Habronema, is transmitted by stable flies that deposit larvae around the eyes, mouth, and prepuce to create ulcerated “summer sores.” Other flies leave larvae in the skin – these warbles (Hypoderma) are identified by a breathing pore directly over the nodule. Cattle are the preferred host of warbles, so horses housed near cows should be monitored. While this sounds like a horror story of “the attack of the creepy, crawly things,” fortunately, all these parasites are eliminated by ivermectin (and in some cases moxidectin) dewormer.
In areas with known problems with pigeon fever caused by Corynebacterium pseudotuberculosis, biting flies are the likely vector that transmits this abscess-forming disease. A vaccine is currently under study but not yet available.
Fine-mesh fly sheets and masks form useful barriers against flies and mosquitoes.
Ticks are known for transmitting ehrlichiosis, Lyme disease, and piroplasmosis. Deer ticks are implicated in Lyme disease (Borrelia burgdorferi) that causes shifting lameness, arthritis, stiffness, muscle pain, fever, behavioral changes, uveitis, weight loss, and some neurologic problems. A serological blood test can help screen horses for infection so appropriate treatment can be implemented.
Besides, daily skin checks and grooming, the best means of lessening tick risks is to reduce wooded habitats that provide ticks with shade and humidity. Also, use permethrin insecticides on your horse, replenishing the application at least every 3-5 days.
In all cases, insect control is important to minimize these risks. Consistent and diligent stall and paddock hygiene is a first line of defense in insect control. Ample drainage of surrounding low-lying and wet areas eliminates insect breeding grounds. Weed whack away plants that harbor sufficient moisture for insect breeding. Reduction in the number and size of breeding areas results in fewer insects. Standing bodies of water can
be managed with mosquito “dunks” and “bits” containing soil bacteria (Bacillus thuringiensis, BTI or Bacillus sphaericus, BS) to control mosquito larvae, black flies and some midges.
Appropriate insecticides are effective when applied topically and/or with barn misters. Fine-mesh fly sheets and masks form useful barriers against flies and mosquitoes. For midges and mosquitoes, protect your horse by stabling him in a fine-mesh, screened-in stall during predominant insect feeding times. Fans pointed at stalls prevent flying insects from circulating or landing in areas of turbulent air. Outward facing fans positioned at barn entrances keep flying bugs from entering in the first place.
In areas of manure deposits, monthly release of non-stinging wasp predators (parasitoids) reduces the number of flies that hatch to adult form – these predators feed on insect larvae.
102 SPEEDHORSE July 2022
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©SUSAN BACHELOR, SPEEDHORSE