While all breeds of horses are susceptible to chorioptic mites, infestation is most commonly seen in feathered breeds. This is because feathers cover the often damp, warm skin surface of the feet and lower legs, which protects the mites and creates the ideal environment. Feathered horses are also more prone to harboring skin issues under their feathers, such as dermatitis and excess skin debris, creating a perfect feeding ground for mites. Chorioptic mites are surface living parasites with chewing mouth parts that bite the outer skin layers in order to feed on skin debris, fat, lymph fluids, and sores. In more advanced cases, mites may concentrate locally under skin folds or crusts, making them more challenging to treat with topical anti-parasitic treatments. Bites from the chorioptic mite cause severe irritation, itching, and discomfort. Infested horses can be seen repeatedly scratching their legs against objects or using their teeth, licking their lower limbs, and stamping their hind legs. Infected horses often show a strong or sudden reluctance to let owners handle their legs.
It is essential to note that mite infestation should not be confused with Chronic Progressive Lymphedema (CPL). CPL is a debilitating condition caused by a buildup of lymph fluid in the lower legs, resulting in progressive swelling with associated skin folds, nodules, and ulcerations. It often affects feathered breeds of horses, including Friesians. The cause of CPL is unknown, but the high incidence in specific feathered breeds suggests a genetic component. The skin folds, nodules, and ulcerations that often occur in horses affected with CPL require very close attention for secondary skin infections and the infestation of chorioptic mites – both of which can exponentially contribute to an acceleration of the disease.
The life cycle of the Chorioptic mite takes approximately 21 days to complete on its host, with eggs hatching within 5-7 days after they are laid. Adult mites can survive off their host in areas such as bedding, tack, blankets, and pastures for nearly 70 days, depending on an adequate food source and environmental conditions. Mites can move incredibly fast from one area of the body to another and often transfer to other horses in close stabling or in shared pastures with the infected host. Mite populations are usually larger in cold weather conditions. Warm and dry circumstances will lower the survival rate of mites. Your veterinarian can confirm the presence of chorioptic mites by taking a skin scraping and examining the sample under a microscope.
TREATING MITES
There are a variety of treatments for chorioptic mites, but clipping or shaving of the feathers on the pasterns is highly recommended regardless of treatment choice. Reducing or removing feathers aids in visibility and thorough cleaning of infected areas, as well as increased skin surface exposure for direct application of topical treatments. Also, a thorough currying, shampooing, and scrubbing of the infected area and entire body before treatment will aid in removing scale and dead skin cell build-up. This essentially reduces or significantly eliminates the mite’s food source and reduces their hiding places. Additionally, any treatment should coincide with moving horses to uninfected stabling or thoroughly cleaning stalls and replacing bedding before returning the horse. Infected pastures should be rested for ten weeks to avoid re-infestation. Common treatments for mites include:
Fibpronil (Frontline) – applied topically as a spray.
Doromectin (Dectomax) – available as an oral or injectable treatment
Ivermectin – available as an oral or injectable treatment
Lime Sulphur Dip– made from Calcium Hydroxide, Sulphur, and water to form a solution that is applied as a topical rinse or “dip”
A 2007 study found that Doromectin and Ivermectin were useful in helping reduce the symptoms of chorioptic mite infestation, but they did not eliminate mites completely. In a 2009 study, various treatment methods were tested on 22 horses that had previously unsuccessfully been treated with both Fipronil and either Doromectin or Ivermectin (or both). Each horse was treated with sulphurated lime dip solution a total of four times at 7-day intervals. Most horses were clipped and shampooed prior to treatment. Horses were assigned a score from 1-10 based on the severity of their lesions and the degree of behavioral signs. The horses were again scored and examined for mites after four treatments. All 22 horses showed a reduction in scores at the end of the trial, and mites were not present in any horse. This response indicates that lime sulfur dip is a highly effective treatment for Chorioptic mites.
Lime sulfur dip is typically sold in a concentrated sulfurated lime solution. This solution kills mites and other parasites and works very well against fungus and bacteria. Unfortunately, it has a powerful sulfur smell and can stain lighter objects and hair. However, it is readily available, easy to use, very effective, and very affordable.
HOW WE TREAT FOR MITES AT FENWAY
Clip or shave the feathers around the pasterns.
Gently curry the horse, focusing on any areas with skin crusts or debris.
Do not pick or disturb scabs.
Shampoo the infected horse’s entire body with anti-dandruff shampoo, making sure to gently scrub any areas with crusts or skin debris.
Prepare your lime sulfur dip using the instructions on the product.
Pour the dip over the entire horse, making sure to reach all infected areas while concentrating on the legs, tail, and mane. Use a sponge carefully on the horse’s face to keep the dip out of the eyes, nose, and mouth.
Do not rinse or towel dry. Let the horse air dry.
Reapply the lime sulfur dip once a week for four weeks.
References:
Control of Chorioptic Mange Mites on Horses, Donkeys, and Mules; Alabama A&M and Auburn Universities.
Comparative study of doramectin and fipronil in the treatment of equine chorioptic mange; DI Rendle, J Cottle, S Love, KJ Hughes.
An open study to evaluate topical treatment of equine chorioptic mange with shampooing and lime sulphur solution; S. Paterson and K. Coumbe.
Chronic Progressive Lymphedema, A. Young.
