Treating Mites

 Treating Feather Mites

by Geraldine Chapman   www.gypsycobsforsale.com

It’s a question you see time and again on forums and in groups “How do I deal with feather mites?” Feather mites – aka Chorioptic mange mites – are common in feathered breeds of horse and the Gypsy Horse is no exception.

Once the horses have them it is very difficult to get rid of them; most likely, it is thought, because they can survive in the environment (pasture, stables, bedding) and so reinfestation is common. Adults can survive for months wherever skin debris accumulates (e.g., bedding, stable floors, saddle blankets). (1) They can also be transmitted between animals and via grooming equipment.

Evidence of mites is more commonly seen in summer months on horses kept outdoors.

Chorioptes mange mites live in the build up of dirt and dead skin cells that collect on the surface of the skin. Mr David Rendle and colleagues at the Glasgow vet school noted that “Their mouthparts are adapted for chewing and they feed on skin debris. Although they do not burrow into the skin, they can cause considerable irritation.” (2)

According to S. Paterson and K. Coumbe “Chorioptic mange caused by Chorioptes bovis is a common pruritic skin condition of the horse. This surface-browsing parasite usually affects the lower legs (leg mange) but can present as a generalized skin disease.” (3)

The mites cause Pastern Dermatitis, also commonly called Scratches, and if left untreated can develop into a nasty condition called Chronic Progressive Lymphodema. Anecdotal evidence suggests however that while some horses with only small infestations go on to develop CPL other more heavily infested horses show barely any sign of mites at all and never develop CPL so it is thought that mites only play a small role in the development of the condition.

Bites from the Chorioptes mites cause severe irritation, itching and discomfort. Infected horses can be seen scratching their legs against objects or using their teeth, licking their lower limbs and stamping their hind legs repeatedly.  A reluctance to let owners handle lower limbs (especially when washing or oiling) is also sometimes evident.

Signs and symptoms of infestation include reddening of the skin (erythema), papules, crust formation, hair loss, skin thickening, lower limb edema or swelling, and other irregular skin lesions” according to vets at Alabama A&M and Auburn Universities, USA. (4)

Obtaining a skin scraping is by far the best method for diagnosing mite infestation. Ask your vet to do this for you.  Diagnosis is important prior to treatment because there are “other diseases that look similar to chorioptic mange are other types of mange, lice infestation, and allergy to fly bites.” (5)

Treatment

Although the mites are most noticeable in feathered horses infestation can occur in all horses, including those with no feather, so any treatment must be applied to all horses on your farm at the same time.

Cleaning the skin, especially round any lesions and crusty areas, is a vital part of successful treatment and most experts recommend fully clipping your horse’s legs prior to washing and applying a topical treatment. “Clipping or shaving the long hair or feathers on the pasterns makes checking the skin easier, lesions more visible, cleaning of affected areas more thorough, and penetration and exposure for direct application treatments better. While owners may prefer not to clip the feathers, particularly in show horses, doing so will drastically improve the chances of treatment success,” say vets at Alabama A&M / Auburn Universities. (6)

Treatment should also coincide with moving animals to uninfected areas, or thoroughly cleaning premises (eg stables) prior to returning the horse after treatment. In the case of pastured horses, turning them out onto fresh, rested pasture might be beneficial. The mite’s life cycle is approximately 3 weeks and is completed on the host; however mites can survive for up to 69 days away from their host making environmental contamination a potential source of reinfection or infection of other horses. (7) Once horses have been moved from infected pasture it should be rested for at least 10 weeks.

Shampooing and scrubbing the skin area clean is advisable to remove scale and dead skin cell build-up before treatment; essentially this action takes away the mite’s food source and reduces their places to hide. Selenium sulphide shampoo (eg. Selsun) is one choice; another is benzoyl peroxide, a keratolytic shampoo; a third is Acetic acid ⁄ boric acid shampoo. Most researchers also recommend shampooing and scrubbing the horse from head to toe as chorioptic mites are known to venture well beyond feathers and legs in some horses. This is sometimes thought to be another avenue of reinfestation – the legs are treated but the mites survive on other parts of the body.

Plan for multiple treatments. Repeating the wash and topical treatment for several cycles will greatly increase your chances of stamping mites out. Repeating the treatment every seven days for four weeks is recommended.

Topical Treatments

Pig Oil

The most common treatment used around the world for Gypsy Horses is “Pig Oil” – a mix of white oil (paraffin) and yellow sulphur. As a treatment for mites it was used as far back as Edwardian times by pig farmers who coated the skin of their pigs with the mixture to get rid of mites. It is still used today in the poultry industry for the same reason. “Sulphur is recommended by Scott (Scott DW, Miller WH. Parasitic disease. In: Equine Dermatology. Philadelphia: WB Saunders, 2003; 321–75.) as an inexpensive effective treatment of infestations of nonfollicular mites in the horse. He describes it as being fungicidal, bactericidal, keratolytic and antipruritic. Its ability to penetrate lesions due to its keratolytic action, as well as its antiparasitic and antipruritic action makes sulphur an excellent potential topical medication to treat chorioptic mange,” note S. Paterson and K. Coumbe in their research on Lime Sulphur Dip treatments. (8)

The oil has the additional advantage of protecting the feather during wetter months.

Sulphur

Pig oil is made by adding a good handful (around 1/2 a cup) of yellow sulphur per litre of white oil. It can be applied directly to the skin from the coronet band to above the knees and hock, taking care to achieve 100% skin coverage and massage well into thickened skin areas and lesions.

Ivermectin / Doromectin

Ivermectin and Doromectin are commonly recommended in forums and groups as treatments for Chorioptic mange mites however there’s limited research to back this up. A 2007 study found they were useful in helping reduce the symptoms of chorioptic mite infestation but they did not eliminate the mites completely. “A comparative study using fipronil spray in a 0.25% solution and doramectin given at a dose of 0.3 mg⁄ kg on two occasions 14 days apart by subcutaneous injection revealed both drugs to be effective in eliminating behavioural signs in affected animals. Although mite numbers were significantly reduced in both groups neither drug completely eliminated mites and there was no improvement in the appearance of the lesions themselves. In a further study, ivermectin paste, given orally, was investigated using three different protocols. All of the horses improved. However despite waiting 3 weeks after therapy to assess the horses there was no significant change in their clinical scores. The advantage of systemic medication is that it negates the need to clip off hair from the pasterns and overcomes the difficulty of applying topical applications on what are often fractious horses. Despite the improvement seen in these studies, none of the drugs completely eliminated mites.” (10)

The limited effect of the drugs may be due in part to the surface feeding habits of the mites – they don’t absorb the full effect of the drug when it is given systematically (by injection or orally); in this respect there is no advantage of injecting the drug over giving it in paste form.

The mythology surrounding Ivermectin and Doromectin being suitable treatments for Chorioptes mites might stem from the drugs’ usefulness combating other mange mite species such as Sarcoptes sp., Psoroptes sp., and Demodectic sp.; producing similar symptoms these mites are rarely found in horses due to their vulnerability to macrocyclic lactone dewormers (ivermectin and moxidectin).

Fipronil

Fipronil is the ingredient in Frontline spray and for a while it became the recommended treatment for Chorioptic mites in horses. It is not rated for use on equines however and is also an expensive treatment with a 500ml bottle costing upwards of $90 here in Australia. “Although therapeutic trials have shown it is successful in alleviating clinical signs, it has been shown to significantly reduce but not eliminate parasites and in studies has not produced any statistical improvement in lesion score.” (11)

Lime Sulphur dip

In a study to evaluate the treatment of chorioptic mange with shampooing and lime sulphur solution researchers tested various methods on 22 horses that had previously unsuccessfully been treated with both Fipronil and either Doromectin or Ivermectin (or both).

In the study some were clipped, shampooed and had the solution applied; others were shampooed and had dip applied; and some only had the dip applied. Of the 22 horses, 20 achieved the lowest pruritus score after treatment 1 – Nonpruritic. The remaining 2 horses achieved the next pruritus score of 2 – Very mild pruritus rare signs of rubbing and chewing without signs of alopecia or excoriation.

All horses shampooed or not, clipped or not, were treated with the Lime Sulphur solution and researchers noted “some horses in group A were neither clipped nor shampooed, and were treated only with lime sulphur. The fact that these horses also responded to treatment suggests that the lime sulphur may have been the most important element of treatment.” (12)

Using a Lime Sulphur solution of 97.5% diluted to a 5% wash (50ml Lime Sulphur solution diluted in one litre of water), researchers first washed the horses and then applied the Lime Sulphur wash via a spray bottle to the wet hair. The solution was not rinsed out. They repeated this treatment every 7 days for four weeks.

Horse owners reported no adverse affects to the horses during the study.

Skin scrapings taken after the four weeks of treatment failed to find any evidence of mites and pruritus (itching) was reduced to nil in all but 2 of the horses; those 2 showed only very mild itching after four weeks of treatment.’

UPDATE (January 2015) : Lime sulphur dip for animals can be bought from the US or UK via various online stores. However, it is not currently approved for use in Australia. You can obtain a permit from the APVMA to import the product for personal use. It is recommended that you obtain a ‘prescription’ from your vet to support the permit request.

Lime Sulphur is sold in Australia as a gardening product; the sulphur component is of a slightly different chemical structure (Thiosulphate sulphur, a clear crystalline structure) to the one described in the dip (sulphur, yellow sulphur) above and I have not found any literature to describe its use and effect on animals.

Lime Sulphur dip is made from Calcium Hydroxide, Sulphur and water to form a solution.

I will include future topical treatments when there is peer reviewed research to support them.

Use a Wholistic Approach

Whichever method an owner chooses for dealing with feather mites it is clear that a wholistic approach is desirable to achieve successful mite eradication.

Cleaning the horse’s premises – be it a stable, yard or pasture – is as important as the treatment itself to prevent reinfestation.  Turning a treated horse back out onto infested pasture will just perpetuate the cycle so resting pasture and rotating horses across the property is good practice. Tack, rugs and grooming kits should also be cleaned.

Treating all horses at the same time is another important aspect to consider. Just as turning horses back out on infested pasture will keep the cycle going, so will running stock back out with carriers who don’t exhibit any signs of mite infestation.


Referrences

  1. Control of Chorioptic Mange Mites on Horses, Donkeys, and Mules; Alabama A&M and Auburn Universities
  2. Comparative study of doramectin and fipronil in the treatment of equine chorioptic mange; DI Rendle, J Cottle, S Love, KJ Hughes.
  3. An open study to evaluate topical treatment of equine chorioptic mange with shampooing and lime sulphur solution; S. Paterson and K. Coumbe
  4. Control of Chorioptic Mange Mites on Horses, Donkeys, and Mules; Alabama A&M and Auburn Universities
  5. Chorioptic Mange in Horses; By Dr. Bob Judd, Texas Vet News
  6. Control of Chorioptic Mange Mites on Horses, Donkeys, and Mules; Alabama A&M and Auburn Universities
  7. An open study to evaluate topical treatment of equine chorioptic mange with shampooing and lime sulphur solution; S. Paterson and K. Coumbe
  8. An open study to evaluate topical treatment of equine chorioptic mange with shampooing and lime sulphur solution; S. Paterson and K. Coumbe
  9. Toxicity of essential and non-essential oils against the chewing louse, Bovicola (Werneckiella) ocellatus; R. Talbert ⇑, R. Wall
  10. An open study to evaluate topical treatment of equine chorioptic mange with shampooing and lime sulphur solution; S. Paterson and K. Coumbe
  11. An open study to evaluate topical treatment of equine chorioptic mange with shampooing and lime sulphur solution; S. Paterson and K. Coumbe
  12. An open study to evaluate topical treatment of equine chorioptic mange with shampooing and lime sulphur solution; S. Paterson and K. Coumbe