There are three words which should spring to mind when considering the cause of an itchy horse; parasites, allergies and, to a lesser degree, infections.
While there are a few conditions which do not fit into any of these categories, most ailments resulting in the intense desire to rub and scratch are due to problems caused by small, wriggling creatures, even smaller irritating organisms, or contact with substances to which the individual animal is allergic.
The old adage ‘common things are common’ is taught to most young veterinary students for a good reason. It is tempting to consider the weird and wonderful, but these are rarely the cause of itchiness. However, if one assumed an itchy horse in the winter time had lice, heel mites or ringworm and in the summer time, sweet itch or another allergy, then even those with no medical training would make a correct diagnosis on a significant number of occasions.
That said, early veterinary assessment, involving thorough history taking, physical inspection of the parts of the body affected and the surrounding environment and appropriate sample taking are necessary in many cases to make an accurate diagnosis and allow prompt treatment.
This is particularly important for itchy patients, in part to minimise the distress caused by severe itchiness and the rapid and severe self-inflicted trauma which can occur in some animals, but also because some conditions are contagious to other animals.
Again, three words should spring to mind; lice, mites and worms. The natural and somewhat understandable response to these words is often shock and a degree of disgust which anyone could suggest that their horse could possibly have such problems.
In reality, fit, healthy and well cared for horses commonly get lice, mites and worms. Lice are primarily a winter, thick coat, cold weather problem, which can be difficult to spot, but are usually light brown and about 2-3mm long (see figure 1). They occur anywhere on the body but are found most commonly in the mane and tail.
Treatment should involve one of a number of anti-parasitic washes, repeating the treatment to kill off any recently hatched eggs after two to three weeks and any in contact animals should also be treated simultaneously. Partially or completely clipping the patient also helps, by removing the warm, protective coat, and treatment of the environment is also necessary.
Mites most commonly affect only the lower limbs up to the knees and hocks. Heel mites are microscopic and quite hard to diagnose under the microscope (see figure 2), but occur commonly in heavily feathered breeds such as the cob. They are hard to completely eradicate but can be kept under control with periodic treatment.
Horses with itchy legs normally stamp their feet, scratch their legs with the opposite limb, or bite at their legs. The effect is to cause secondary bacterial infections which are often mistaken for mud fever. Any horse which appears to have mud fever in dry weather is likely to have heel mites.
Treatment involves managing the secondary infections, ideally by clipping out the feathers and treating with topical antibacterial washes, along with using anti-parasitic washes. While there are no products specifically licensed to treat heel mites, there are anti-parasitic injections and topical sprays used in other species which are effective. One of the long-acting horse wormers has also recently been found to be effective in treating heel mites. As with lice, the environment must also be treated.
Pinworms appear to be making something of a comeback, despite the availability of effective wormers, possibly due to the development of resistance resulting from their inappropriate or overuse.
The itchiness comes from the egg-laying activity of the adult worms around the bottom, causing the affected animal to rub its tail and bottom area against solid objects (see figure 3), often damaging the skin and tail hairs. While adult worms are not often seen, egg deposits can be visible as crusty material stuck to the skin around the bottom.
Treatment involves washing the area daily with warm water to remove eggs and using appropriate wormers as recommended by your veterinary surgeon. Good stable hygiene involving regular washing of hands and grooming equipment also helps. It may be necessary to continue treatment for several weeks to eliminate the infection.
Allergic skin disease has many causes, with itchiness being one of the more common clinical signs. Broadly speaking, allergies can be divided into three categories: those caused by;
Any route can result in itchiness. Investigating allergies can be difficult and both blood testing and skin testing is available. Blood testing for allergies is popular and readily available, but remains contentious and not an exact science. Allergy skin testing is probably more accurate (see figure 4) but can be expensive and is not widely available.
Treatment of allergies can be difficult, in part because it is not always easy to find the specific cause. Reducing exposure by removing the substance from the environment is also not always possible. Medical treatment generally involves using anti-inflammatories such as steroids, along with antihistamines and a selection of other substances which reduce the body’s allergic response.
De-sensitisation therapy has become popular in recent years. Depending on the results of allergy testing, the patient is injected with a solution containing small quantities of the offending chemical, theoretically gradually desensitising the immune system so eventually it does not respond anymore. Some cases appear to respond well to immunotherapy.
Sweet itch, an allergic reaction to proteins in midge saliva is a well-recognised and common allergy seen across the UK, mainly between May and September, although severe cases can persist throughout the year.
Although the mane and tail are the most commonly affected areas (Figure 5), some animals can be itchy everywhere. Management changes such as keeping patients away from trees, ponds and slow-moving waterways where the midges congregate, along with stabling at dawn and dusk and using specially designed rugs which cover the whole body, help reduce the problem in many patients. Concurrent drug therapy may still be necessary in some patients, although some do not improve until they are moved away from the immediate area to where there are fewer midges.
Bacterial and fungal skin problems, notably mud fever, rain rash and ringworm, can result in irritation and mild pain which can lead to rubbing and scratching. The resultant self-inflicted trauma perpetuates the cycle of irritation. Sometimes these infections occur as a primary problem such as an outbreak of ringworm, while they can also be secondary to an underlying skin problem, such as the dermatitis of the lower legs commonly seen in association with heel mite infection. Skin scrapes, hair samples and skin biopsies all play their part in helping identify the cause. Treatment may involve both the use of antibiotics and anti-fungals, along with identifying and treating any underlying causes.
There are many products available to treat itchy skin in horses, some available from your vet, others available online and from feed merchants. For many itchy skin conditions, drug therapy is integral in their short-term treatment and long-term control. However, many management changes also play a crucial role in dealing with skin problems, without which drugs alone will not be sufficient. Many veterinary surgeons do not charge for telephone advice, so take the time to discuss the roles of medication and management in dealing with itchy patients.
Acknowledgements for photographic contributions:
Richard Morris MRCVS Fenwold Veterinary Practice, Spilsby, Lincs
Laura Evans MRCVS, Chapelfield Veterinary Partnership, Brooke, Norfolk