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3c_COMMON INFECTIOUS SKIN DISEASES

By Anita Simpson,2014-06-21 11:16
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3c_COMMON INFECTIOUS SKIN DISEASES

    COMMON INFECTIOUS SKIN DISEASES

? The treatment and control of skin diseases form an important part of the daily

    duties of veterinary surgeons especially with regard to shelters and rehoming

    centres. The details given here apply to both shelters, rehoming centres and

    individually owned pets.

    A. MANGE:

? There are two types of mange commonly seen in dogs: Sarcoptic and Demodectic

    Mange.

    1. SARCOPTIC MANGE (SCABIES):

a) Aetiology:

? This is one of the most common skin diseases seen in shelters and is caused by the

    Sarcoptes scabiei (var canis) mite. ? It is highly contagious spread mostly by direct contact between animals and also

    indirectly by kennel buildings, bedding, feeding bowls and grooming instruments.

    ? The mites can survive off the host for up to 3 weeks depending on environment.

    b) Clinical signs:

? The dogs are highly itchy (pruritic) with reddening of the skin (hyperaemia) and

    scaling/ crusting signs are seen typically 21-30 days after exposure.

    ? Lesions are seen especially on the face, ears, limbs, ventral abdomen and chest the

    disease can spread rapidly although it rarely involves the dorsum of the back.

    ? Most patients have a generalised enlarged lymph nodes (lymphadenopathy).

    ? In prolonged cases darkening (hyperpigmentation) of the skin is common.

    ? Humans can sometimes develop areas of inflammation and itchiness (pruritis) at

    in contact sites these will improve as the dog is treated.

    ? The disease is more prevalent in hotter months.

    c) Diagnosis:

? If you lightly scrape the edge of the dog’s ear with a thumb nail a powerful

    scratch reflex is elicited (with the hind legs) this is called the “Pinnal-Pedal

    Scratch Reflex”; 75-90% of dogs with scabies have this reflex. This is more of a

    test for itchiness (pruritis) than scabies but it goes down well with the owners.

    ? History and clinical signs.

    ? Superficial skin scrapings should be taken to confirm suspicions: a) Either clip the hair or use scissors in hairy dogs but be careful not to clip away

    the crusts, look for red spots (small papules) with yellowish crusts on top do not

    choose sore (excoriated) sites.

    b) Primary sites for taking scrapings are the elbows, hocks or ears. c) Multiple scrapings should be taken from these lesions.

    d) Apply a little liquid paraffin to the area and to a clean, blunt scalpel blade and

    scrape the lesion. Smear the scraping over a microscope slide and examine first

    on low power x10 increasing the power to x 40 to detail any suspect mites. e) Confirmation can be difficult as the severity of the irritation is not always

    proportional to the number of mites present. Sometimes you need to take several

    scraping from different sites before mites are found. However, one mite is

    diagnositic!

    ? Skin biopsy techniques can also be used although rarely practised. ? In some cases diagnosis is often confirmed by successful response to treatment as

    mites are not always found.

    d) Treatment:

    ? Due to its highly contagious nature any dogs suspected of having scabies should be

    isolated e.g. infectious skin room.

    ? Due to the highly contagious nature of this disease it is a good idea to treat in contact

    dogs although this is not always possible in a shelter environment it is highly

    recommended.

    ? Long haired dogs should be clipped to allow for penetration of shampoos and washes.

    ? Common treatment regimes include:

    a) 1% solution Ivermectin injections 10mg/ml (“IVOMEC”) at a dose rate of

    0.02ml/kg (0.2mg/kg) given under the skin (subcutaneously) at weekly to

    fortnightly intervals depending on the severity of the condition. Normally at least

    34 injections are required. This is one of the best options in shelters (it is used at

    the SPCA, Hong Kong) due to the low cost and ready availability of this product.

    PLEASE NOTE Ivermectin injections at the above dose rate should not be used in

    Collies such as Shetland Sheepdogs and Rough Collies as it can result in

    depression, ataxia, tremors, paresis, recumbancy, stupor, coma and in some cases

    death.

    b) Milbemycin oxime (“MILBEMYCIN”) at doses of 2mg/kg orally either twice at a

    14 day interval or three times at weekly intervals (this is more expensive

    compared to Ivermectin but can be used in Collies).

    c) Diamide (“AMITRAZ”) at a 2cc/litre of water dilution. The wash should be

    applied to a dry coat using a sponge and allowed to dry naturally. DO NOT

    RINSE OFF. The wash is a poison so instructions should be followed carefully.

    Gloves should be worn and the dog should not be allowed to lick the coat. The

    wash should be applied once to twice weekly depending on the severity for at

    least 4-6 washes. This is a cheap option but time consuming if several dogs are

    affected.

    d) Selamectin (“REVOLUTION”) two applications (according to size) at a 30 day

    interval cured 93-100% of cases in a recent trial. As with Milbemycin this is a

    more expensive option and generally reserved for owned animals.

    ? Other treatments include antibiotics or oral antifungals if secondary bacterial or

    fungal dermatitis is present.

    ? Corticosteriods at anti-inflammatory doses can be used e.g. Prednisolone at

    1.1mg/kg once daily for the first 2-3 days to control pruritis but should not be

    used long term particularly when bacterial skin infection is present.

    ? Antiseborrheic shampoos can be used to remove debris and crusts.

    ? It is very important to treat until clinical signs have resolved as recurrence is

    highly likely.

e) Prevention and Control:

? Due to the highly contagious nature any dogs suspected of having scabies should be

    isolated (skin isolation room).

    ? It is a good idea to treat in contact dogs if possible.

    ? As the mite can survive off the body for up to 3 weeks depending on environmental

    conditions it is wise to thoroughly clean all bedding and feeding bowls with strong

    disinfectants. If possible the environment can be sprayed with diamide (“AMITRAZ”)

    at a 2cc/litre of water dilution.

2. DEMODECTIC MANGE:

a) Aetiology:

    ? Demodex canis mites are present in normal skin in very small numbers i.e. 70%

    of normal animals carry Demodex with no clinical signs.

    ? Why do some dogs develop demodecosis while others do not?

    ? There is an increased incidence in certain breeds such as Sharpeis, West Highland

    White Terriers, Dobermans and Mini Pinschers.

    ? To understand the disease it is important to understand the mode of transmission

    that is by direct contact from the bitch to pups in the first 2 3 days of their lives.

    For this reason affected dogs should not be bred from.

    ? Mites live in hair follicles and unlike the sarcoptes mite are unable to survive

    away from their host.

    ? The actual skin disease is associated with immune deficiency (an inherited

    specific T-cell lymphocyte deficiency) which allows the mite to multiply into

    large numbers and in older dogs it is often associated with other diseases such as

    allergies or conditions which lower the animal’s immunity for example cancer or

    liver disease.

    ? Other factors effecting the development of demodecosis include oestrus,

    parturition, chemotherapy and endo and ectoparasites.

    b) Clinical signs:

    ? There are 2 forms of disease localised and generalised.

    ? LOCALISED FORM appears as patches of hair loss with or without reddening

    usually around the eyes (periocular), head, mouth and forelimbs. This form is not

    normally itchy. Most lesions occur at 3-6 months of age, the course is benign and

    most cases resolve spontaneously. It is rare for true localised demodecosis to

    develop into the generalised form. Occasionally dogs have demodectic otitis

    externa (ear disease) only.

    ? GENERALISED FORM: can be subdivided into 3 types:

    a) Juvenile: this form occurs at 3-12 months of age showing numerous lesions on the

    head, trunk and legs with hair loss, scaling, redness and skin thickening. Often

    secondary bacterial or fungal infections are present.

    b) Pododermatitis: appears as foot lesions only with thickening of the interdigital

    region, swelling, hair loss and infection common in Old English Sheepdogs and St.

    Bernards.

    c) Adult: which occurs at any age from 2-14 years and is usually associated with

    debilitating or immunosuppressive diseases, therefore, always look for an

    underlying cause such as hypothyroidism, hyperadrenocorticism and malignant

    neoplasia.

    c) Diagnosis:

? Clinical signs and breed predisposition.

    ? Deep skin scrapings similar to as described for Sarcoptes although it is very

    important to do deep scrapings from several sites and to squeeze the affected skin

    before scraping to bring the mites to the surface. Diagnosis is made by

    demonstrating large numbers of adult mites or an increased ratio of immature

    forms to adults. Please note a single mite can be consistent with normal skin

    unlike Sarcoptes.

    ? A hair pluck can also be taken using forceps and the root examined under the

    microscope for mites using oil and a cover slip (this is simpler particularly if the

    animal is difficult to control or aggressive).

    ? Skin biopsies can be performed if demodex is highly suspected but not found on

    scrapings or plucks but this is more expensive and time consuming.

    d) Treatment:

    ? The localised form in young dogs will normally resolve spontaneously. There is

    no evidence to suggest treating the localised form prevents the development of the

    generalised form later in adults.

    ? Consider any underlying causes in adults.

    ? Although the mite is not very resistant in the environment it is difficult to reach in

    the hair follicle.

    ? Antibiotics should be used when pyoderma is present often for 6-8 weeks but

    unlike Sarcoptes corticosteriods are contraindicated.

    ? Skin scrapings should be taken at 2-4 week intervals to determine the

    effectiveness of any treatment.

? Any of the following treatments should be continued for 30 days or longer beyond

    negative skin scrapings (from 4-6 sites).

    ? Treatments include:

    a) Benzoyl peroxide gel (“OXYDEX” or “PYOBEN” gel) used for the localised

    form (if the owner is concerned) should be gently massaged into the area daily for

    4 weeks after which scrapings should be repeated and show a reduction or

    elimination of mites if the treatment is working.

    b) Diamide (“AMITRAZ”) used as for sarcoptic mange but at a higher concentration

    of 4cc/ litre of water. In small dogs it is advisable to apply the wash to only half

    the body on one day. Washes can be given as often as twice weekly in severe

    cases. The minimum period for treatment is 6 to 8 weeks.

    c) Oral Ivermectin 10mg/ml (“IVOMEC”): the half life of Ivermectin in canine

    serum is 1.8 days and although many adverse reactions are seen in the first 4 days,

    levels of Ivermectin continue to increase for 6 weeks before reaching equilibrium,

    and adverse effects can be seen up to 10 weeks after commencing treatment.

    Initially a low dose is given increasing the amount daily over 3-4 days to the

    treatment dose of 0.03ml/kg per day.

    ? DAY 1: initial dose of 50mcg/kg (0.005ml/kg)

    ? DAY 2: 100mcg/kg (0.01ml/kg)

    ? DAY 3: 150mcg/kg (0.015ml/kg)

    ? DAY 4 and thereafter: 300mcg/kg (0.03ml/kg)

    d) Milbemycin oxime: various studies have been performed using doses from 0.5-

    2mg/kg daily for 60 up to 300 days. Clinical cure rates vary greatly from 15-92%.

    This treatment is expensive so not recommended in a shelter environment.

    ? As mentioned with scabies “Amitraz” and oral “IVOMEC” are preferable in

    shelter situations due to the lower costs of drugs. The oral ivermectin is obviously

    less time consuming compared with the diamide washes.

    ? Please note in cases of generalised demodecosis dogs who achieve negative

    scrapings can not be declared cured until at least 12 months after treatment has

    stopped. Recurrence is likely.

    ? Demodex has also been reported in cats (Demodex cati) where it tends to cause

    patchy areas of hairloss especially around the eyes, head and neck. This condition

    is rare and as for dogs is diagnosed by skin scrapings. Treatment involves clipping

    long haired cats and weekly shampoos with “SELEEN” Shampoo (selenium

    sulphide) until negative scrapings and a clinical resolution is achieved.

    e) Prevention and Control:

? As demodex is not contagious isolation of affected animals is not necessary

    (unlike scabies).

    ? Affected dogs should not be bred from.

    ? Advise spaying of bitches as pregnancy and oestrus have been shown to

    contribute to relapses.

    B. DERMATOPHYSIS (RINGWORM):

a) Aetiology:

? Is a very common disease seen in especially in puppies and kittens.

    ? 3 fungi cause the majority of cases of ringworm in cats and dogs:

    a) Microsporum canis - majority of cases (especially in high humidity)

    b) Microsporum gypseum

    c) Trichophyton mentagrophytes

    ? These fungi are transmitted by contact with infected hair, scales, fomites such as

    brushes or bedding or fungal spores in the environment.

    ? The fungi tend to attack hair follicles (also nails and keratin of the skin). The hair

    is shed and the fungus spreads out giving the classical circular lesion (but these

    circular lesions are not always seen).

    ? The usual source is an infected or “carrier” pet but can be rodents particularly in

    the case of Trichophyton mentagrophytes.

    ? Studies show up to 27% of owned cats and 88% of stray cats can carry the disease

    without clinical signs.

    ? These “carriers” are often detected when either the owner or incontact dog or cat

    develops ringworm lesions.

    b) Clinical signs:

? The classical clinical signs are circular patches of alopecia (hair loss), with or

    without itchy skin (pruritis), reddening of the skin, scaling and crusting.

    ? The lesions may just be localised on the head, ear flaps (pinnae) or feet or can

    spread to the whole body (especially in immune-compromised pets).

    ? Lesions can also be seen on owners or kennel workers (zoonotic).

c) Diagnosis:

? History and clinical signs such as a recent visit to a cattery or groomers.

    ? Woods Lamp (U.V. light) as approximately 50% of cases of M. canis fluoresces

    bright apple green. Care, however, as soaps, creams and bacteria such as

    Pseudomonas may fluoresce. It is very important to warm the U.V. light up for at

    least 5 minutes prior to testing and the exam is best performed in a darkened room.

    ? Microscopic examination of a swab or hair pluck from a lesion (placed on a slide

    with 10% Potassium Hydroxide and gently warmed). Using a coverslip focus up

    and down on damaged hairs looking for hyphae inside the hair shafts and spores

    inside or around the hair shafts (the spores look like someone has smeared caviar

    onto a chopstick). It is possible to use stains to improve visualisation of fungal

    structures e.g. “QUINK” Blue Ink (normal ink used for writing pens), Methylene

    Blue or Lactophenol Cotton Blue Stain.

    ? If these tests are negative the hair sample should be cultured.

    ? Fungal culture of hair samples from a lesion (or brushings using a clean

    toothbrush “Mc Kenzie” method which is especially useful where carrier status is

    suspected). Culture for up to 10-14 days in 20-25 degrees celsius in a dark place.

    Please note the container for culture should not be airtight. Media used include:

    a) Sabouraud agar.

    b) Or a special “fungassay” media e.g. “DERMAFYT” test is more common in

    general practice which is Sabouraud’s agar with added ingredients to inhibit

    overgrowth with saprophytes and bacteria. The media will change colour from

    yellow to red in the presence of fungus. This is the best diagnostic method for

    ringworm. However, be careful with false positives and negatives.

    ? It is advisable to check any colony cultured under the microscope. Clear sticky

    tape is pressed sticky side down gently onto the culture and placed onto a drop of

    stain e.g. Methylene Blue and evaluated under the microscope. Microscope oil

    can be placed directly onto the sticky tape there is no need for a coverslip.

    ? Biopsies of the skin stained with Periodic Acid Schiff (PAS) will often reveal

    hyphae in the skin around hair follicles but as with demodex this is more

    expensive and time consuming so it is often easier to treat.

    d) Treatment:

? Clip any longhaired animals particularly cats but care should be taken not to

    damage the skin as this can encourage the spread of disease. Owners should be

    warned the disease may worsen 7-10 days after the clipping.

    ? Ringworm in healthy dogs and short haired cats will often undergo spontaneous

    remission within 3 months. Likewise some kittens and puppies showing mild

    symptoms will self cure without treatment as they grow older. But warn re

    zoonotic potential.

    ? Griseofulvin (“Funtrol”) is the systemic treatment of choice at a dose rate of 15-

    50mg/kg orally per day for both dogs and cats. It should be given in food and the

    addition of oil to the food aids in its absorption. It should not be given to pregnant

    or very young animals (less than 8 weeks). Himalayans, Siamese and Persians

    may be predisposed to side effects and avoid use in cats with concurrent FIV

    infections. At least 1 2 months of treatment is necessary but in some cases over 4

    months have been given, particularly in longhaired cats with widespread lesions.

    ? Griseofulvin is the drug of choice in shelter environments due to its low cost.

    ? In cases of Ringworm which are non responsive to griseofulvin other drugs used

    include:

    a) Itraconazole (“SPORONOX”) 5-10mg/kg once daily by mouth.

    b) Ketoconazole (“NIZORAL”) at 5-10mg/kg every 8-12 hours by mouth.

    These drugs are more expensive compared to griseofulvin and as such tend to be

    reserved for resistant cases.

    ? Topical preparations used on both cats and dogs include:

    a) Miconazole 2% cream (“FUNGTOPIC”) applied twice daily to lesions up to a

    1cm margin of normal clinically healthy skin; the cream is useful when only one

    or two lesions are present.

    b) Chlorhexidine and Miconazole shampoo (“MALASEB”) this is used on the whole

    body once or twice weekly. Good for more widespread lesions.

e) Prevention and Control:

? Keep all animals in a healthy state with good nutrition and low stress; avoid

    overcrowding and implement regular parasite control.

    ? It is a good idea to treat in contact dogs and cats if feasible.

    ? Separate infected pets and if possible identify carriers by performing

    “toothbrushings” on all cats but this is not always possible due to expense and space.

    At the SPCA we separate all clinically affected cats in a special ringworm room.

    ? Treatment of the environment is also important e.g. M. canis can remain viable in the

    environment for up to 18 months. This includes thorough vacuuming and steam

    cleaning of carpets plus disinfection of walls and floors with bleach at 1:29 dilution or

    another fungicide. It is of often necessary to destroy leads, bedding and grooming

    equipment.

C. FLEA (AND TICK) DERMATITIS:

    a) Aetiology:

    ? External parasites:

    a) Fleas = Ctenocephalides canis/ felis (cats and dogs)

    b) Ticks = Haemophysalis leachi (dogs only)

    ? Fleas and ticks can cause a variety of problems ranging from mild skin disease to

    life threatening anaemia.

    ? Control of these pests is of utmost importance.

    ? Both survive by feeding on their host’s (dog or cat) blood.

    ? Normally ticks and fleas stay on the cat or dog to feed the rest of the time

    remaining in bedding, carpets and under furniture where they lay eggs.

    b) Clinical signs:

    ? Flea bite dermatitis commonly presents as scaling, redness and hair loss along the

    back (dorsum), tail head, hind legs and ventral abdomen (Sarcoptes rarely affects

    the back).

    ? The dog or cat is allergic to the flea saliva; licking and scratching results in

    trauma to the skin surface setting up secondary bacterial and fungal infections.

    This condition is particularly bad in the spring when the flea eggs which have

    over wintered hatch and the adults look to feed (although in tropical climates they

    are an all year problem).

    ? Ticks bites may also result in itchiness (pruritis) plus secondary infection with

    bacteria and fungus due to self trauma.

    ? Other diseases and problems related to these parasites include:

    a) Fleas: weight loss, lethargy, tapeworms (Diphyllidium caninum) and anaemia in

    severe infestations

b) Ticks: are responsible for “TICK FEVER” a disease where microscopic parasites

    (Babesia canis/gibsoni and Erhlichia canis) carried by ticks cause the breakdown

    of red blood cells resulting in fever, anaemia and death if left untreated.

    c) Diagnosis:

? From clinical signs.

    ? The presence of fleas or flea faeces in the coat.

    ? If fleas are suspected but not visualized coat brushings placed on wet blotting

    paper will show a reddish tinge.

    ? Other tests include intra dermal skin testing, however, this is rarely necessary.

    ? The presence of ticks on the coat is usually diagnostic due to the slow movement

    of these parasites (unlike fleas). They are often found in warm moist areas such as

    the ears and groin.

    d) Treatment:

? Routine antibiotics used in bacterial dermatitis caused by fleas (or ticks) include

    Amoxycillin (“AMOXIL”) at 11-22mg/kg three times daily by mouth and

    Cephalosporins (“CEPOREX”) at 10-30mg/kg twice daily by mouth.

    ? If the animal is very itchy and a lot of self trauma is present corticosteriods can

    be used in the short term e.g. Prednisolone at 0.5mg/kg by mouth twice daily or

    1.1mg/kg once daily gradually reducing the dose to alternate days by which time

    the fleas should have been eliminated from the environment and further challenge

    removed.

    ? Antibacterial shampoos are often employed once to twice weekly e.g.

    Chlorhexidene (“PYOHEX”). ? FLEA AND TICK CONTROL ON DOGS/CATS: concentrates on the

    eradication of fleas from both the animal and its environment.

    a) Fipronil (“FRONTLINE SPRAY”) is effective for up to 12 weeks in dogs and 8

    weeks in cats (at the SPCA we tend to recommend monthly treatments). This

    product will still remain on the coat after bathing 2-3 times and is also effective

    against ticks for 2-3 weeks. It can be used safely in pregnant and lactating bitches,

    in puppies from 2 days of age and kittens from 7 weeks. The dose is 2-4 sprays

    per kg (ticks need a higher dose) applied all over the body, parting and ruffling

    the coat to get the spray to skin level. The coat should be allowed to dry naturally

    or blow dry do not wash off. The product is flammable so do not smoke!! b) Fipronil (“FRONTLINE PLUS SPOT-ON”) is applied in a concentrated dose (an

    oil like preparation) to the back of the neck and left to absorb this gives protection

    for approximately one month (2-3 weeks in the case of ticks).

    c) Selamectin (“REVOLUTION”) applied as a spot on the back of the neck which

    gives protection against fleas for around one month. This product does not appear

    to be as effective against fleas as Fipronil and has no action against ticks. It is

    useful for low risk animals e.g. old dogs living in apartments. The benefit,

    however, is that it can also prevent heartworm plus treat ear mites and sarcoptic

    mange.

    d) “PREVENTIC” (Amitraz 9%) tick collar for dogs only gives up to 4 months of

    very effective protection against ticks. Not effective against fleas. e) Flea and Tick Collars are available for both dogs and cats and provide protection

    for varying periods depending on the brand. They are, however, less effective

    than sprays (with the exception of “Preventic”) and in some animals can result in

    local hair loss and irritation. They are not suitable for young puppies and kittens.

    Flea powders such as Pyrethrin are generally less effective than sprays but are

    suitable for small puppies and kittens.

    f) Flea and tick dips for example “ASUNTOL” are only suitable for dogs; they can

    be used as often as once weekly. Gloves should always be worn and the directions

    for use should be followed very carefully to prevent poisoning. g) It is important to note using more than one flea/tick preparation at one time such

    as a collar and dip can lead to overdose, poisoning and even death. Always follow

    the manufacturers instructions carefully.

    h) At the SPCA we use Fipronil spot-on due to time saving factors compared to the

    spray; we reduce the cost by using the largest size titrated into pots and have a

    chart of ml/kg bodyweight to enable easy, accurate and safe dosing by staff. All

    dogs and cats in our rehoming centres receive a monthly dosing (at the same time

    they are also dewormed and dogs are also given heartworm prevention

    medication).

    ? ENVIRONMENTAL CONTROL: Fleas and ticks only remain on the dog or cat

    to feed the rest of the time they live in the home environment where they lay eggs

    which go on to hatch and continue the cycle. The following are products we

    regularly recommend to treat the environment:

    a) Flea bombs, foggers and sprays for example “AMERICARE” after two initial

    applications (2-4 weeks apart) this product will give effective flea control for up

    to 6 months. An added bonus is some products will also kill cockroaches and

    other pests. Always remove animals and people from the area when using the

    above plus cover fish tanks and food. Make sure the area is well ventilated after

    use.

    b) Diluted flea dips can be used to wash towels and bedding in addition to spraying

    areas where the pet lives such as a balcony or run.

    c) Pest control companies for example “RENTOKILL” will treat your house, garden

    and yard particularly useful at the start of warm weather to prevent the eggs from

    hatching.

    d) “PROGRAM” (LUFERON) a once monthly oral flea treatment for dogs and cats.

    It does not directly kill fleas but is a larvicidal drug (blocking the formation of

    larval chitin). As a result the normal build up of flea population is prevented. It

    does not kill the fleas directly. It is particularly useful for cats living in flats that

    do not go outside. It can be used safely with other topical flea/tick preparations

    such as “Frontline”.

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