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How I treat: equine chorioptic mange
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ACVSC Proceedings Dermatology Chapter Science Week 2005
Janet Littlewood
Equine chorioptic mange is caused by the surface-living mange mite Chorioptes bovis
var equi. Mites are principally found on the lower limbs of horses with feathered
lower limbs, causing variable irritation and erythema, alopecia, exudation and
crusting, although some infested animals may show only seborrhoea. Although leg
mange is the usual clinical manifestation, infestation of the body may also occur.
Clinical signs and mite numbers are higher in winter months, with mites thriving in
groups of stabled horses and also surviving for prolonged periods off the host, in the
presence of epidermal debris, and dark, humid and cool conditions.
There are no licensed products for this disease in the United Kingdom, necessitating
the use of drugs off label, according to the “cascade” guidance on prescribing. There
are a number of options open to the clinician, with varying amounts of evidence in
support of each.
Flumethrin is licensed for bovine chorioptic mange in Eire and mainland Europe
and is available as a sheep scab and tick product in the UK; the 6% solution can be
diluted 1:900 and applied at a dose rate of 30ml/kg, repeated in 14 days.
Doramectin, eprinomectin and moxidectin have claims for bovine chorioptic mange
in the USA. However, clinicians in the USA often use ivermectin at 0.3mg/kg per os
weekly on 4 occasions.
A published clinical trial with oral ivermectin paste given orally at the dose of
0.1mg/kg per os daily for 7-10 days or 0.2mg/kg twice at 2 week intervals,
eliminated mites in 74% of treated horses, with only occasional mites in the
remaining animals, whereas large numbers of mites remained in the control group
(Littlewood et al 1995).
Topical 2% lime sulfur washes are also used in the US, weekly for up to 6
applications. A pilot study using 1% selenium sulphide shampoo was effective in
treating 7 infested horses. Whole body washes were given on three occasions at 5
day intervals; the hair was clipped from the limbs of two of the horses (Curtis 1998).
The author has previously shown that chlorhexidine bathing had no curative effect
in infested horses, although it assisted in controlling secondary bacterial infection.
On the basis that fipronil is effective for a similar disease in dogs, cheyletiellosis, as
well as for harvest mite infestation, 0.25% fipronil spray was used to treat a case of