“Susceptibility to Chorioptes bovis (CB) differs between horse breeds. Those that suffer most have abundant feather, such as the Ardennes, Clydesdale, Friesian, North Swedish, Shire, and Tinker. According to Dan Christensson, a parasitologist, CB is a very common condition.
“To confirm the presence of CB one needs to get a sample of the affected area of skin by scraping it deeply until it starts to bleed. The sample is placed in glycerine or liquid paraffin and then viewed under a microscope. Only one-third of tests prove posetive, which means that the horse still may be infected even though the biopsy has not confirmed the presence of mites. This can occur because if your sample was sent away to a laboratory any mites present can have died during transport. If the horse then shows symptoms of complications of CB, they may show up in the sample in the form of a fungal infection. There are proven cases of CB in both Friesian and Tinker horses. Hans Kinndahl, a veterinary surgeon, has personal experience of CB in his own Tinker horse.
“CB is contagious and can easily by transferred by physical contact, by holding in a common stable or by grooming horses with the same brush. It is disputed how long CB mites can survive in the absence of a host, but can be from 24 hours up to 3 weeks, depending upon weather conditions, according to information received. Mites thrive when it is cool and damp. One should not confuse CB with Shoroptes bovis (SB) which is far more contagious. There are at present no restrictions in cases of CB and reporting is not compulsory though there is no harm in reporting any occurrence to the County Veterinary Surgeon, as many vets know little or nothing about CB.
“In mild cases, CB symptoms can be similar to those of grease. The difference is that the affected area usually is higher up than the pasterns, which is the part usually affected by grease. Crustation breaks out especially around the fetlock joints and canons, but can spread up the legs. Even bald patches can occur on other parts – on its belly in front of the sheath and even on the head. CB can also affect the mane and tail, where it looks like eczema. You can tell when a horse has been infected as it starts scratching its tail and mane and stamps the ground. The horse is bothered by itching which, in more severe cases, can be so tiresome that it is psychologically irritated and gets bad habits such as weaving or just switches off and becomes apathetic.
“What is typical of CB is that summer symptoms are milder while those in February-March are more severe, when it’s usually cold and snowy - which is not when grease is most prevalent. As grease can be treated and cured, one should be vigilant if the horse does not improve following treatment. CB on the other hand is much more difficult to deal with and can only be relieved (but not cured) by treating the infected area as for fungus and grease.
“If you want to rid your horse of CB, we would recommend treatment by Dan Christensson, Parasitologist at SVA (the National Veterinary Institute) here in Uppsala (Sweden) (tel.no. +46 (0)18 674000). He recommends Frontline, though this is not registered for use on horses, only for cats and dogs. It is forbidden for horses treated with Frontline to be slaughtered for human consump-tion. Spring-Summer is the best time to treat horses for CB as it is then that they are less troubled by CB; in other words, they have fewer active mites to get rid of. To be on the safe side, one should treat the horse three times, at 1-2 week intervals. It takes about 16 days for the eggs to hatch but this is not confirmed. Each treatment should consist of Frontline spray, aimed at the infected area on the legs. Spray first and then rub it well into the skin, wearing rubber gloves. The remedy is then transported via the subcutaneous fat upward in the horse, which is why it is important to apply the spray low down on the legs even if it is the mane and tail that are affected. If other horses are stabled with the infected horse, then these too should be treated, even if they are symptom-free.”
This is a free translation of an article published in the Swedish Shire Horse Society’s members´ magazine Giganten (The Giant), No. 2, 2002.

Present authors´ comment on the above-quoted text
We have tried another product – Sebacil (Bayer) which is also registered for use on dogs, pigs and sheep, with good results. An intensive course of treatment using the de-worming product Ivomectin can also give good results but we recommend that you consult your veterinary surgeon first.