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.
? There are two types of mange commonly seen in dogs: Sarcoptic and Demodectic
1. SARCOPTIC MANGE (SCABIES):
? 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.
? 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
? 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.
? 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
? 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
3–4 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
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
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
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:
? 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
? 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.
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
? 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
? 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.
? 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
? 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):
? 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).
? 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.
? 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
? 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
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
C. FLEA (AND TICK) DERMATITIS:
? 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 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
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.
? 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.
? 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
? 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
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
? 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
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
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”.