In recent years, a new generation of flea control products has become available which has enhanced our ability to control infestation and skin disease associated with this parasite. Drugs such as imidacloprid (Advantage), fipronil (Frontline) and lufenuron (Program), when used correctly, are able to eliminate fleas from all but the most susceptible households. Before these drugs were launched, it was true to say that the vast majority of cases of feline itch was due to fleas. It may still be true to state that the commonest cause of feline skin disease is the flea. However, there is no doubt that as a second opinion dermatologist, I am seeing fewer cats that stop itching when you apply an insecticide, and am recognising a stubborn group of 'feline skins' where a much more detailed and meticulous diagnostic approach is needed to find the diagnosis.

It is probably wise to discuss the manifestations of itch (or pruritus) in the cat before considering the causes of non-flea induced pruritus as cats have an almost bewildering range of skin changes associated with itch. Furthermore, in some instances it can be very difficult to differentiate feline skin disease due to pruritus from skin disease induced by other causes. For example, in man and dogs, hair-loss is almost always hormonal in origin. In cats hormonal skin disease is so rare as to be virtually non-existent. Hair loss in this species is invariably caused by excessive self-grooming due to a generalised feeling of `itchyness' — but often the owners are unaware that the cat is grooming a little more aggressively and a little more frequently than a normal cat would.

MANIFESTATIONS OF FELINE PRURITUS

• Itching, scratching and self-induced skin damage
• Symmetrical hair loss
• 'Miliary' dermatitis
• 'Eosinophilic granuloma complex'

(rodent or indolent ulcer; linear granuloma and eosinophilic plaque)

Miliary dermatitis is an itchy dermatosis often associated with a greasy, dandruff-filled coat and characterised by tiny 2-3 mm diameter crusts throughout the body surface. Rodent ulcers are erosive lesions affecting the upper lip which in severe cases it looks as though the lip has been `eaten away'. Linear granulomas are areas of crust and inflammation which, uncannily, form ruler straight lines under the chin or clown the rear aspect of a hind leg. Eosinophilic plaques are angry looking, exuding red areas of skin usually on the trunk.

All of these manifestations of itch look completely different but can all be caused by the same things — in most instances the cause is fleas but other parasites and allergies can be involved. Some cats may have more than one manifestation of disease present simultaneously, eg, indolent ulcer and symmetrical hair loss.

WHAT CAN CAUSE FELINE PATIENTS TO ITCH OTHER THAN FLEAS?

• Food intolerance/allergy
• Housedust and pollen allergy (atopy)
• Insect bites
• Ear mites
• Other mites
• Bacterial infections (In addition there is a number of very rare causes which will not be discussed in this short report.)

FOOD INTOLERANCE/ALLERGY

No-one knows the exact mechanisms by which certain foods can make animals and humans itch. Allergy may be involved but some authorities have speculated that the pruritus may result from chemical reactions to the food or to additives and preservatives. However, it is well recognised that feeding some pruritic cats on a food that they have not been habitually exposed to previously can cure itching. This can cause a number of practical problems. Cats hunt and may be fed by neighbours. The diet has to be fed for many weeks in order to make a diagnosis. Ideally a home-cooked diet should be fed and this may be expensive, especially if there are several cats in the household (obviously they all should be fed on the test diet).

ATOPY (ATOPIC DERMATITIS; DUST AND POLLEN ALLERGY)

This is another somewhat mysterious feline skin disease. In man and the clog it is far better understood; we have all met people with eczema or asthma. The diagnosis is based on eliminating other possible causes from the investigation (ie, feeding a 'hypoallergenic' diet and enforcing rigid flea control.) Allergy testing is performed on cats but is rather unreliable.

Atop' is incurable and life-long medication is needed to prevent unacceptable discomfort to the cat. Treatment with essential fatty acids and antihistamines is successful in the minority of cases and in many instances long term corticosteroids are needed. If an allergy test has successfully identified the offending air-borne particles then vaccine therapy is an option.

INSECT BITES

When considering insect bites as causes of skin disease, it should be remembered that wasps and bees are insects and their bites can lead to dramatic painful swollen skin. Other insects include fleas (of course!), midges, flies and mosquitoes. The flying insects usually bite relatively hairless areas such as the bridge of the nose and ears. Mosquitoes have been reported to cause an eosinophilic granuloma-like reaction on the bridge of the nose of some cats. It is possible that some flea control products may have a modest repellent effect.

EAR MITES

Ear mites are well known as the major cause of otitis externa in young cats and in breeding colonies. However, it is also possible for the mites to meander onto the skin surface around the head and cause skin disease at these sites. As cats sleep curled up, infestation and dermatitis affecting the rump and tail may occur.

OTHER MITES

Harvest mites are a recognised cause of skin disease in cats in areas with chalky soil in late summer and autumn. These tiny orange dot sized mites are visible to the naked eye and usually found between the toes and in Henri's pocket of the ear flap. In other parts of the world, fur mites occur and Noedres cati (now virtually extinct in the UK) may be a problem.

BACTERIAL INFECTIONS

The prevalence of bacterial skin disease in cats is unknown but there has been a small number of reports of spectacular recovery following antibiotic treatment in pruritic cats. This is an area in need of much more research as, in the past, it has been assumed that cats are very resistant to bacterial skin infections as they are regarded as being 'clean' and fastidious animals.

SUMMARY

Despite the introduction of new highly effective flea control products, fleas still remain a significant cause of feline skin disease. However, in some instances, animals fail to respond favourably to insecticidal treatment and the owner and veterinary surgeon have to embark on a detailed search to discover the cause of the problem.