The Mucocutaneous System

Some definitions:

Alopecia- loss or lack of hair, partial or complete.

Pruritus- The sensation of itching which provokes scratching, chewing, rubbing, licking etc. Usually due to inflammation.

Seborrhea- A complicated disorder in which skin cells accumulate as scale. Associated with defects in sebum (skin oil) production and quality, and excessive skin cell production. Dry and oily forms are seen.

Pyoderma- Bacterial skin infection. Can be classified as superficial or deep depending on severity.

ECTOPARASITES

Cheyletiella

Also known as Walking Dandruff, these are large, superficial mites, and are found on dogs (C. yasguri), cats (C. blakei) and rabbits (C. parasitivorax).

Diagnose using a low power microscope and coat brushings or sellotape collections.

Treatment- selenium sulphide shampoo (Seleen). ivermectin (Ivomec), fipronil (Frontline)- (not rabbits), amitraz (Aludex) Milbemycin (Stronghold). Treat the environment with an insecticide spray and clean up bedding.

ZOONOSIS- rash on the owners body as the mites penetrate clothing. Cannot live on humans. Mites often found on young Boxers. (and sometimes persist in older ones).

Sarcoptes scabei. (Sarcops)

=Scabies. Mites found on the dog, usually. They burrow in the skin and can be transmitted on bedding or fomites. Foxes are a source for domestic dogs. Irritation starts on the ears and elbows then spreads over the body. The dog becomes smelly, said to be like "mouse urine" VERY itchy.

Diagnosis difficult as the mites may not be found on scrapes. Often treated just-in-case.

Treatment- Selamectin (STRONGHOLD (Pfizer)) Spot-On is now the treatment of choice for Sarcops. It can be used on all breeds. Monthly treatments are usual and it may take several treatments to clear the mites. Vet-Kem sponge-on is an older treatment which is also licensed.
Some bedding treatment desirable.

ZOONOSIS- rash usually on arms, but cannot live on humans.

Notoedres cati

The cat version of sarcops, affects mainly the head and ears and very uncommon.

Diagnosis as for dog sarcops

Treatment- Ivermectin injection, selenium sulphide bathing, Stronghold spot-on.

Demodex

Demodex canis (occasionally D. cati seen in the cat). All dogs are infested with demodex as it is passed from mother to pups in the first few days of life. Disease is rare, however, as the immune system deals comfortably with the majority of the mites. 3 syndromes are found, however:

Localised- A focal hair loss, usually with very little pruritus, and often around the head. Said to be self limiting but responds well to treatment by bathing. Young dogs.

Generalised - Widespread hair loss often with secondary scale, pyoderma, pruritus. Treatment usually involves a combination of anti-mite shampoos, follicle flushing and degreasing shampoos, and antibiotics. Some dogs with this form never recover. Young dogs.

Adult onset - localised progressing to generalised, but 90% of these have an underlying disease such as cancer or hormone problems and the demodex is secondary.

Skin scrapes are used to monitor the success of treatment.Because Demodex infestation reflects an immune system "blind spot", animals with demodex are NOT contagious to other normal dogs.

Otodectes cynotis

The dog and cat ear mite. Usually seen in young animals, and causes a thick brown waxy exudate, often mistaken for blood by the owners. Kittens most commonly carry this. Very pruritic.

Diagnosis - seen using the otoscope, or on wax smears. Clearly visible to the naked eye, but hates light so will seek out the depths of the ear.

Treatment - most ear drops kill the mites, probably by suffocating them in oil! It is necessary to treat over a 3 week period as the eggs are resistant, and take 3 weeks to hatch.Stronghold Spot-on is also licensed as a single treatment to kill ear mites (put it on the skin in the ususal place, NOT in the ear).

Ixodes Ricinus - the sheep tick

Can be vectors of an important bacterial disease- Lyme disease, caused by Borrelia. Ticks are insects and so must moult to grow. They have four stages- egg, larva, nymph, adult. The tick hangs onto vegetation until it senses warmth, motion, carbon dioxide, i.e. a host. It then attaches and sucks blood for a day or two before dropping off and moulting. Local swellings of the skin occur as a reaction to the saliva.

Treatment- apply alcohol, spirit or an insecticide, then detach by twisting out the mouthparts. There are several types of tick remover available. Prevent using Frontline (preferably the SPRAY not the spot on variety) or anti- tick collars.

Ticks are an important consideration in the PETS scheme. Click HERE to see my PETS scheme page

Ticks can infest humans (Lyme disease is a Zoonosis), but not directly from the pet.

Lice (pediculosis)

Various species, very host specific and little survival in the environment. There are two types- biting lice which chew the skin and sucking lice which feed on blood.

Dog- Linognathus setosus (sucker), also Trichodectes canis (biter)

Cat- Felicola subrostratus (biter)

Animals with lice are very pruritic, but although the lice are easily seen with the naked eye, a careful hunt may be necessary. The pinnae are usually a good place to start, and watch out for the small white eggs attached to hairs.

Treatment - Lice are susceptible to most antiparasitic drugs, but the eggs are resistant, so at least one repeat treatment after 10 days is desirable.

Harvest mites

Only the larvae are parasitic; they emerge in the fields during late Summer, and cause facial and pedal irritation. They can be seen as small orange dots, particularly around the ears. In cats check in Peter's pocket at the back of the ear.

Treatment - any anti parasitic, but avoiding exposure is the key to preventing recurrence.

FLEAS

The commonest flea is the cat flea (Ctenocephalides felis), found on dogs and cats. Dog, hedgehog and bird fleas are also found occasionally. Fleas are responsible for an enormous amount of skin disease, either directly or because the pet becomes sensitive to flea saliva (flea allergic dermatitis, miliary eczema). The flea life cycle is egg-larva-pupa-adult. ONLY the adult flea is on the host. Therefore MOST FLEAS ARE IN THE ENVIRONMENT. A healthy flea can live for up to 3 weeks and lay up to 30 eggs a day. Egg laying begins soon after the flea acquires a host. The pupal stage may be able to survive for a year or more, waiting for a host, and then hatch out and be in mid hop within 3 seconds.

Treatment- Treat the animal with an effective and long lasting insecticide, e.g. Frontline or Advantage.

ABSOLUTE WASTES OF TIME AND MONEY- powders, herbal products.

MOSTLY WASTES OF TIME AND MONEY- shampoos, collars, sprays (particularly shop bought)

It is vital to treat the environment AS WELL AS THE PET:-

Sprays- use one with a knock-down and an insect growth regulator.

Lufenuron (Program)- Administered to the animal but prevents the hatch of the larva from the egg. Very effective unless there is constant pick up outside the home environment, or a stream of non- treated pets through the house.

Polyborates- a dehydrating agent. Non toxic and effective, applied rather like shake-n-vac.

Hoovering. The eggs are not sticky!

Fleas are not a zoonosis (cannot complete their life cycle), but will bite humans, characteristically on the lower leg. This is because they are not transferring from the pet, but the larvae in the environment think the owner is a dog or cat, and they hatch-and-hop as the client passes by.

They may be a source of FeLV transmission between cats.

Small mammal skin parasites (usually treated with Ivomec)

GUINEA PIGS- Biting lice; sarcoptic type mange (Trixicarus caviae)

RABBITS- Cheyletiella, Sarcops, Ear mites

HAMSTERS - Demodex

RATS AND MICE - Sarcops type mange

GERBILS - Demodex, sarcops, ear mites

HEDGEHOGS- Chorioptic mange, fleas

FERRETS - Sarcops

HORMONAL SKIN DISEASE

Classic hormonal skin disease causes non pruritic bilaterally symmetrical alopecia. This is because hormonal problems generally stop hair regrowth after the natural loss of a hair. The flanks are usually affected first, and a biopsy is diagnostic (but non-specific as to hormone).

Hypothyroidism.

A common but difficult to diagnose disease. Classic hair loss is found along with a variety of other signs including: weight gain, lethargy, slow heart, high cholesterol, mild anaemia, muscle weakness (etc., etc., etc.). It is unfortunately rare to have an easy to diagnose case.

Diagnosis- measurement of blood levels of thyroxine or thyroid stimulating hormone (TSH). These can be normal, however, and so the best test is a TSH stimulation test in which blood samples are taken before and after injecting TSH. Poor response indicates hypothyroidism.

Treatment- supplementation daily with Thyroxine (Trade name = Soloxine).

Hyperadrenocorticism (Cushing's disease)

Overactivity of the adrenal cortex (remember the medulla produces adrenaline). The overactivity arises either from a small pituitary tumour producing too much ACTH, or from an adrenal tumour itself (Rarer). This results in too much cortisol in circulation, so the animal show signs of an overdose of steroids- Hair loss, pot belly, polyuria + polydipsia, weakness, polyphagia, occasionally diabetes. This disease generally affects middle aged terrier types and other small to medium size breeds.

Diagnosis- classic clinical signs in many cases. Measurement of circulating cortisol is unreliable, so dynamic testing is performed, either- 1/ Dexamethasone suppression test- an injection of the steroid drug dexamethasone fails to suppress internal steroid production in affected dogs.

or- 2/ ACTH response test- an injection of ACTH produces massive rises in cortisol production in affected dogs.

Treatment- the drug Trilostane is used to stop steroid synthesis. Surgery to remove the adrenals is also used, and other drugs are in development.

Cats are also affected very occasionally.

Growth Hormone (GH) Deficiency

A rare cause of symmetrical hair loss. Long primary hairs are lost first. Hair regrowth can occur at biopsy sites.

Diagnosis- measurement of GH in blood.

Treatment- Very expensive supplementation. May respond to castration if a male.

Sex Hormone Alopecia. 3 Types

Oestrogen responsive in Females. Due to either poor oestrogen production or lack of cell receptors. Seen in Dachs., Boxers, Airedales.

Hyperoestrogenism- older bitches with oestrogen secreting ovarian cysts and tumours.

Hyperoestrogenism- In males with Sertoli cell testicular tumours. Often cryptorchids.

Feline endocrine alopecias

These are very rare. The widely held belief that a lot of cats get hormonal alopecia arises from the once widespread use of megoestrol acetate (Ovarid) to treat all cat skin diseases. The reasoning was that since Ovarid is a hormone, then it must be treating a deficiency. In fact most feline hair loss is allergic in origin (and the rest is psychological), and Ovarid is exerting its effect as an anti-inflammatory drug.

Hyperadrenocorticism is occasionally seen in cats, and also a condition called alopecia areata, in which there are non itchy patches of hair loss.

PYODERMA

Common in dogs and rare in cats, literally means pus-in -the -skin. Seen most in young dogs (acne-like), heavily skin folded breeds, and German Shepherds. Caused By Staphylococci. (Staphylococcus intermedius is its full name)

Surface pyoderma- such as Hot Spot eczemas and skin folds. Surface ointments and shampoos are sometimes all that are necessary, but oral antibiotics are usually needed.

Superficial pyoderma- Puppy acne and folliculitis, seen in short coated breeds particularly. Oral antibiotics are used for at least a week beyond apparent cure.

Deep pyoderma - a serious and sometimes life-threatening disease, involves the underlying dermis. Local versions are anal furunculosis, and interdigital cysts. May need antibiotics at high doses for up to 12 weeks.

Feline pyoderma. Seen on the chin in some cats, and is an acne-like disease, which responds to antibiotics, but can be quite difficult to cure completely.

RINGWORM

Fungal skin infection.

In the dog, usually Microsporum canis, M. gypseum, or Trichophyton species.

In the cat, usually M. canis, occasionally Trichophyton. 

Fungi only colonise dead tissue, i.e. keratin, and are destroyed by inflammation. They are slow growing, may incubate for up to 8 weeks, and usually colonise damaged areas first. Infection in cats may be asymptomatic.

Diagnosis- clinical signs vary, and Staphylococcal infection is usually mistaken for ringworm. The commonest presentation is as a crusting, pruritic area on the face or feet. Fungal culture on a selective medium is best, and indicator dyes in the medium are used to tell the difference between harmless fungi and dermatophytes. A Woods lamp (ultraviolet) is also used, looking for a characteristic apple green fluorescence in affected hairs, but only Microsporum species fluoresce, and only 60-80% of these will show up.

Treatment- Spontaneous cure can occur. The usual treatment is Griseofulvin (Fulcin, grisovin) for 4-6 weeks. The dose is given twice daily, and is best absorbed with a fatty meal. It is important to clean the environment and disinfect with bleach (spores on any shed hairs). Long haired cats may need clipping out. Griseofulvin is teratogenic - can cause foetal abnormalities so it should not be used in pregnant animals, and should not be administered by pregnant owners.

Program (Lufenuron) is reported to work against Ringworm as a single double dose in cats or as a whole 6 month course given at one go to dogs.

In dogs, enilconazole washes can be used (Imaverol) instead.

ALLERGIC DERMATOSES

Flea Allergic Dermatitis

Said to be the commonest skin disorder in small animals. This is not a reaction to lots and lots of fleas, this is a Type II hypersensitivity reaction to the fleas' saliva. Intermittent exposure to fleas is thought to be worse than constant or no flea infestation, and very few fleas are necessary to cause this problem.

Signs- usually severe pruritus and self-inflicted damage around the back and rump over the tail base. Fleas can usually be found in dogs, but cats with FAD may groom so obsessively that no fleas can be found. This is the commonest cause of "miliary eczema" in cats.

Diagnosis- flea dirt in the coat (use wet white paper, scrub the animal over it and watch for tell-tale red spots appearing). Also, intradermal testing will show up flea sensitivity, and a blood test is becoming available for use in dogs, detecting flea-specific immunoglobulin.

Treatment- see the parasite lecture notes. Signs in the animals can be controlled with corticosteroids if necessary.

Atopy.

Allergic reaction to inhaled and percutaneously absorbed antigens, such as house dust, human and animal skin flakes (dander), pollens. It is thought to be inherited, and is much more common in some breeds such as English Setters, Retrievers / Labradors and German Shepherds. The onset is usually in young dogs, and may be seasonal.

Signs- uniform redness and irritation in the face, feet, axillae and inguinal / ventral abdominal regions. Otitis externa.

Diagnosis- Blood sampling or skin testing.

[Intradermal Skin Testing- Sedated with Rompun, Domitor, Ketamine etc. but NOT ACP. The test is performed on the lateral thorax / abdomen . The coat is clipped out, and a grid of felt tip pen dots is marked out. Various pure solutions of allergen are injected (0.05ml) intradermally at each site, and the reaction is measured after 15-30 minutes, with a further check at 24 hours. Each allergen is compared with a saline injection (negative control) and histamine (positive control).]

Treatment- Corticosteroids, Essential fatty acids (Efavet, etc.), occasionally antihistamines. It is possible to use the information from skin testing to try to desensitize the animal with regular injections of specific allergens. This is successful in about 60% of cases.

 Food hypersensitivity

Uncommon, and usually seen in young dogs and acts up to about 18 months of age.

Signs- Often facial pruritus, but may look just like atopy.

Diagnosis- Selective elimination diet (such as fish and potato), selected depending on the pet's usual diet.

Treatment- avoid the food!

 Contact dermatitis

Rare in dogs (but common in people!) This takes some time to develop, so usually seen after prolonged exposure to something (carpet dye, detergents, fabrics, plastics).

Signs- pruritus at the sites of contact

Diagnosis- Patch testing applied to clipped skin, but this is difficult as this is a delayed reaction, and signs only appear after 24 hours.

Treatment- change the environment.

 Primary irritant dermatitis

Chemical irritation by caustics or irritants such as petrol, tar, oil, cement.

Treatment- wash off with copious amounts of water and detergent if oily.

 Urticaria

Immediate hypersensitivity to plant or insect stings. Present as "fat heads, fat feet" etc.. or as red plaques over the body. Usually treated with a short acting corticosteroid.