Table of Major Systems, and
pain, fever, lameness
(Cat Scratch Disease)
none in cats
moist, honking cough ('kennel cough")
to conceive, abortion, swollen testicles, swollen lymph
cats, all mammals
(often bloody), vomiting, reluctance to eat
eyes, nasal discharge, sneezing
cats, dairy animals
death in newborns, diarrhoea, mastitis.
potential low but possible
cells, whole body Anaemia,
of gums, fever, lethargy, haemorrhage
passed directly from pet to person
cats, ferret, people,
primarily; ulcers, inflammatory bowel disease
weakness and pale mucous membranes
cats, farm animals, people
liver, whole body
variable: fever, lethargy, increased thirst, vomiting
rarely cats, people
body, joints, heart
lethargy, lameness that shifts from leg to leg
direct spread from pets to people
system may be infected; lungs, skin
Wasting, emaciation, coughing, skin wounds
coughing; failure to conceive and abortion
respiratory, whole body
draining wounds, difficulty breathing
dogs, wildlife (esp. prairie dogs), humans
nodes, respiratory, whole body
lymph nodes, high fever, cough, weight loss
Mountain Spotted Fever
people, rarely cat
vessels, whole body
bruising, bleeding from nose, lameness,
directly transmitted to people from pets
cat, reptiles, people
puppy and kitten death Group A is rarely passed from human
Cat, Human, other
ears, reproductive, whole body
scabs, abscesses of skin; odour in ears
rarely dog, human
nodes, liver, whole body
swollen lymph nodes, lethargy, icterus
stomach pain, depression, rapid death
Joanne Howl, DVM Editor
Walt Ingwersen, DVM, DVSc, Diplomate ACVIM
BACTERIAL SKIN INFECTIONS IN SMALL ANIMALS
Bacterial skin infections are common in small animal veterinary
practice. These vary in severity from a transient involvement of the
skin surface only to deep discharging infections which are
non-responsive to therapy and which commonly relapse. The most
frequent causal organism in bacterial skin infections in pets is
Staphylococcus intermedius. S. aureus is the species usually
isolated in man. Escherichia coli and Proteus species may also play
a role in pyoderma's. S. intermedius is a normal resident in the pet
- nasal cavity, oropharynx, and the perianal region. It can be a
transient resident in other sites especially if there is trauma to
the area. The organism is probably transferred to these sites from
the oral and anal mucosae during grooming. A dense hair coat has a
protective effect, preventing the pathogenic bacteria from having
access to the skin. This may explain why certain pyoderma's are
common in glabrous areas (e.g. impetigo in abdominal skin). Normally
skin is highly resistant to colonisation by bacteria. Inflammation
of the skin results in temperature changes and increased skin
permeability. Colonisation is thus favoured which in turn results in
the production of toxins and irritants and a cycle of further
inflammation, infection, etc. In subcutaneous abscesses in cats
which are usually from fighting, Pasteurella multocida is the
principle bacterium found.
Pyoderma's can be frustrating to deal with. They can be
non-responsive to therapy and relapse repeatedly. Pursuing the
underlying predisposing factors and using general principles of
therapy, including antibacterials is necessary to successfully
manage pyoderma's. Gram negative bacteria are generally secondary
invaders which are controlled by therapy effective against
Staphylococcus. Pseudomonas, however, is a Gram negative bacterium
which is difficult to eliminate and requires specific therapy.
of bacterial skin disease
Pyoderma can be classified as localised or generalised, primary or
secondary, and also according to the depth of the affected tissue.
Surface pyoderma's include acute moist dermatitis ('hotspot'), and
intertrigo (fold dermatitis). Superficial pyoderma involves the
epidermis and often the hair follicles. Included here are impetigo
and superficial folliculitis. It is important to treat these cases
adequately to prevent recurrence and progression to deep pyoderma.
Deep pyoderma may be an extension of a surface or superficial
pyoderma, or may occur after a primary insult. Deep pyoderma's
include muzzle folliculitis, pyotraumatic folliculitis, bacterial
pododermatitis, German Shepherd Dog pyoderma, and subcutaneous
This involves colonisation of the epidermis only. Clinical signs
include erythema, papules, pustules, and alopecia. Self-excoriation
may result in larger alopecic areas. The hallmark finding,
especially early in the disease process, is intact pustules (Figure
1). These may enlarge in the epidermis and rupture, resulting in a
circular alopecia with scale at the periphery - 'epidermal
collarette'. Gently removing the roof of an intact pustule gives an
uncontaminated sample. An impression smear can be made from the
pustule contents. A stain such as Kyro-Quick stain (Kyron) enables
cell cytology to be performed. To achieve a pure growth of the
causative organism, samples for culture are taken from intact
Acute moist dermatitis
Acute moist dermatitis is commonly encountered in practice. There is
usually a single erythematous lesion, starting in the haired areas,
which may rapidly enlarge. Erythema, folliculitis and crusting may
be evident under the hair coat beyond the edge of the alopecic area
(Figure 2). The ability to spread rapidly like a veld fire has lead
to the term 'hotspot'. The rump, dorsum, tail base, and flanks are
the most common sites involved. Fleas are usually incriminated.
Erythema of the skin indicates enlarged dermal blood vessels which
probably further attract fleas to an easy blood meal. For this
reason, corticosteroids at anti-inflammatory levels are often
sufficient on their own. In early hotspots topical glucocorticoids
may be sufficient. Where systemic glucocorticoids are required, a
covering antibiotic effective against skin pathogens should be
considered. Self-excoriation and the resultant hair loss may make it
difficult to find evidence of flea involvement, but strict flea
control is necessary. Deeper pyoderma's involving usually the
peri-auricular and facial areas (known as 'pyotraumatic dermatitis')
require more intensive investigation and therapy.
Skin fold pyoderma (intertrigo)
Any of the body folds (e.g. lip, facial, tail, and vulva fold) can
be involved, but also the interdigital spaces of the paws. Irritant
substances and lack of ventilation combine with sweating,
self-excoriation, and eventually swelling of the folds. Where these
folds rub together, as in the paws, intense inflammation results.
Colonisation by bacteria and the yeast organism, Malassezia
pachydermatis causes further inflammation. Where swollen folds rub
together, as in the paws, a cycle of inflammation, pruritus,
swelling, and infection is perpetuated.
This has recently been recognised as a distinct entity which
involves the oral mucocutaneous junction. There can also be
concurrent mucocutaneous involvement of the anus. Superficial
pustules and crusts involve the full extent of the lips as opposed
to lip fold pyoderma which is less extensive, involving the dimple
(fold) in the lip only. Ulceration leading to deeper infection may
occur. Histopathologically, the dermis contains a dense,
predominantly plasmacytic, interface dermatitis. Pigmentary
incontinence may also be present.
Superficial pyoderma is a deeper invasion of bacteria with
involvement of all layers of the epidermis. The hair follicle is
invaded and the hair shaft may fracture resulting in alopecia. In
both cat and dog pyoderma's, Staphylococcus is the most frequently
isolated bacterium. Cytology and culture may fail to reveal a
causative organism. This is indicative of non-Staphylococcal, or
aseptic pyoderma's which can mimic a bacterial pyoderma. Pemphigus,
juvenile cellulitis, sterile nodular panniculitis, subcorneal
pustular dermatosis, eosinophilic folliculitis and furunculosis,
sterile nodular pododermatitis, linear immunoglobulin A pustular
dermatosis and sterile eosinophilic pustulosis have all been
described as aseptic pyoderma's or 'pyoderma impersonators' occurring
The term 'impetigo' is used to denote a superficial pyoderma
affecting dogs which have not yet reached puberty. Puppies from 6
weeks to 7 months old are affected. The clinical finding in impetigo
is the presence of pustules on the ventrum which are not centred on
the hair follicle. Verminosis, systemic disease, and nutrition may
all play a role. However, often no inciting cause can be found. The
problem may self-cure, however, antibacterial shampoos and
antibiotics are sometimes necessary. Impetigo may occur in older
pets that are immuno-incompetent. In these patients, an
immunosuppressive condition should be searched for.
In folliculitis, the infection is limited to the hair follicle. The
hallmark finding, a pustule with a hair in the centre, may only be
found early in the disease process. Superficial folliculitis occurs
in young and older pets, and is generally secondary to other
conditions. Allergic skin disease, demodicosis, hypothyroidism and
lack of adequate hygiene should be investigated. Control or
eradication of the underlying causes can be combined with systemic
antibiotics, antibacterial shampoos and/or antiseborrheic shampoos.
Superficial spreading pyoderma
Expanding papular and macular areas indicate a spreading S.
intermedius pyoderma (Figure 3). Differentials include other common
dermatoses such as dermatophytosis, demodicosis, and scabies. In the
early stages pustules and epidermal collarettes are seen, sometimes
with hyperpigmentation of the centre. These may coalesce to form an
alopecic area which may be pruritic. Intense erythema indicates a
hypersensitivity to Staphylococci present within the pustule (Figure
1). The pruritus associated with this hypersensitivity is so intense
that the condition is only seen in a pet that has had adequate
restraint (e.g. with an Elizabethan
collar). Self-excoriation often
results in a penetration of the infection into the dermis. The
circular lesions of superficial pyoderma (Figure 3) have a close
resemblance to ringworm lesions and hence this pyoderma is commonly
misdiagnosed as a dermatophytosis. Features which assist in
distinguishing between these two are listed in Table 1.
Features which assist to distinguish between superficial
pyoderma and dermatophytosis
||trunk, ventrum mostly
||head and limbs mostly
||more in number
||less in number
|Responds to cephalexin
||usually a single
||allergic skin disease,
demodicosis insect bites, dermatophytosis
Deep pyoderma occurs when the infection extends through the
epidermis or hair follicle and involves pyogenic inflammation of the
dermis or subcutis (Figure 4). The hair follicle ruptures and the
infection spreads into surrounding dermal structures (furunculosis),
or becomes disseminated through the deeper dermal tissues into the
subcutis (cellulitis). Since demodicosis may be an underlying cause
in all deep pyoderma's, repeated skin scrapings are necessary.
Although deep pyoderma is the rarest form of pyoderma, it is also
the most severe form, requiring intensive systemic therapy.
Muzzle folliculitis and furunculosis
In dogs, muzzle folliculitis and furunculosis is more prevalent in
puppies approaching maturity (Figure 5). However, in cats, this
condition known as 'feline acne', may occur at any age. In dogs,
mild cases self-cure, but furunculosis and cellulitis require both
topical and systemic therapy. Since this condition is found in short
coated dogs, it is usually not necessary to shave the area. Benzoyl
peroxide in a shampoo or gel is effective. Malassezia dermatitis
should be treated with topical products containing an antifungal
agent such as miconasole (Daktarin, Janssen-Cilag), systemic
antibiotics effective against S. intermedius are required and short
courses of corticosteroids (anti-inflammatory doses) may be
necessary. In dogs, this condition will usually resolve after
puberty and adequate therapy but may, as in cats with feline acne,
be a lifelong problem.
Feline acne (Figure 6) is considered a defective primary
keratinization in areas rich in sebaceous glands. The presence of
comedones and follicular casts in the skin of the chin of cats
confirms the condition. Invading organisms include Pasteurella,
Streptococcus, Malassezia, Demodex and dermatophytes. Feline acne
can be distinguished from eosinophilic granuloma by the fact that
comedones are not present in the latter disease. Cleansing and
flushing with benzoyl peroxide and chlorhexidine are beneficial.
Topical treatments include the antibiotic, mupirocin, and the
antifungals, cotrimazole and miconazole. An ointment containing
benzoyl peroxide combined with miconazole (Acnidazil, Jannsen-Cilag)
is useful. The systemic antibiotic clindamycin (Antirobe, Pharmacia
& Upjohn) can be administered for a four to six week course.
Synthetic retinoids have been recommended for stubborn cases.
However, as in man, a cautious approach to this last group of drugs
Pyotraumatic folliculitis and furunculosis
As the term denotes, this involves trauma (abrasion,
self-excoriation) and a purulent discharge. It is often secondary to
otitis externa, foreign body, atopy, and dietary allergy. Initially,
there may be an acute moist dermatitis which extends deeper,
especially in the facial and subauricular areas (Figure 7). Golden
retrievers, bull mastiffs, and Rottweilers are at risk.
Self-excoriation, wound soiling and contamination, inadequate
therapy, and demodicosis can all result in pyotraumatic
folliculitis. E coli, Proteus, and S. intermedius are often present.
Shaving must extend beyond the border of involved skin. After
careful scraping for mites, both topical and systemic therapy is
administered. Ear canals and surrounding areas must be thoroughly
evaluated. Sedation, bandaging up the paws and other forms of
restraint are necessary to minimise self-excoriation.
Pressure point pyoderma
Localised infection of the elbows and hind limbs may be precipitated
by lying on hard surfaces. A blanket on hard surfaces does not
provide sufficient protection for the pressure points in large and
giant breeds. A foam rubber mattress (covered in an impervious
material) provides an insulating bedding.
Deep bacterial infections in the paws may be an extension of
intertriginous pyoderma of the interdigital spaces. Malassezia
dermatitis may be involved, either alone, or as a mixed infection.
Other inciting factors include trauma, foreign bodies, atopy,
contact allergy/irritant dermatitis, neoplasia and migrating
nematodes. Deep draining fistulas and painful pododermatitis may
require sedation or even general anaesthesia to allow for deep
scrapings to rule out demodicosis. Bacterial paronychia is common in
cats as a nail bed infection. Chronic nail bed infections may be
secondary to underlying immune modulated disease and the
immunosuppressive viruses should be screened for. Furunculosis of
the paws indicates deep pyoderma with/without demodicosis. However,
dermatophytoses, particularly those caused by Trichophyton species,
should always be considered - especially in Jack Russell terriers,
hunting dogs, digging and rooting dogs and where one paw only is
This is encountered in rooting/digging dogs and outdoor/hunting
dogs. Factors to be investigated include trauma, geophilic fungi,
insect/arthropod hypersensitivity, auto-immune and allergic skin
German Shepherd Dog (GSD) pyoderma
GSD pyoderma is the term given to frequent episodes of deep
folliculitis and furunculosis in the German Shepherd Dog and its
crosses. Hallmarks of this disease are middle aged and older GSDs
and their crosses of either sex with a furunculosis, discharge and
pain (Figure 8). It may be an extension of a surface pyoderma and
begin as a mild infection, often unnoticed in the thick coat. Later,
serous and bloody discharges cause matting of the coat, which
becomes 'glued' to the lesions. Scarring can result in permanent
deep draining fistulas. GSD pyoderma has been described as a
syndrome of disproportionate severity and with frequent relapses.
The familial nature and severity should be made clear to owners.
Recent studies have shown that affected dogs have unusual lymphocyte
characteristics indicating an immunodeficiency. Other inciting
factors must be searched for. Ectoparasites, especially fleas, but
also scabies and demodicosis are the most common predisposing causes
in the author's experience.
Abscesses are common in cats, and are usually from fight wounds.
Pasteurella multocida is the most common bacterium isolated.
Subcutaneous abscesses must be lanced, drained and flushed. P.
multocida is usually well controlled with penicillins. However, deep
abscesses e.g. tail root abscesses, and those involving anaerobic
bacteria require extended courses of clindamycin.
Rare bacterial infections
Atypical mycobacteria which are present in the soil may invade the
subcutaneous skin. Feline leprosy is caused by rat bites. Nocardia
is a filamentous bacteria which may affect cats and dogs.
Creams, ointments and gels
Localised pyoderma's such as fold dermatitis, feline acne, otitis
externa and impetigo may respond well to topical creams, ointments
and gels. Kanamycin, neomycin, bacitracin, polymixin B,
nitrofurazone and mupirocin are examples of topical antibiotics.
Mupirocin (Bactroban, SmithKline Beecham) is especially useful in
certain stubborn surface pyoderma's. Cat fight abscesses should be
lanced, drained and flushed with a 2 % hydrogen peroxide and/or a
0.5% chlorhexidine solution. Dilute povidone iodine solution may
also be used.
Baths, soaks and shampoos
Clipping and shaving the coat and cleansing with antibacterial
shampoos will be beneficial. Antibacterial shampoos are particularly
beneficial in surface and superficial infections. Chlorhexidine is
both anti-bacterial and anti-fungal and is available in a shampoo (Pyoderm,
Virbac). In deep pyoderma's, pyodemodicosis, and stubborn cases of
furunculosis, the follicular flushing effect of benzoyl peroxide may
assist. In severe furunculosis, such as GSD pyoderma, it is
essential to shave the effected areas (even if this is the whole
body!). The lesions can be painful and this may have to be done
under deep sedation or even general anaesthesia. Shaving exposes
areas of infection previously hidden under a dense coat (Figure 8).
It may be necessary to warn the patients owners as fragile skin may
peal away leaving unsightly deep draining fistulas. Exposure of the
deeper lesions is necessary, however, to allow for adequate
cleansing and access for topical therapy. Washing helps to remove
crusts, thereby improving ventilation and drainage and it can also
have a soothing effect. Chlorhexidine is particularly effective and
often less irritant. Avoid corticosteroids because of the
possibility of underlying immuno-incompetence and/or demodicosis.
The systemic antibiotics that have been advised are the
fluoroquinolones and cephalexin.
S. intermedius, is the most commonly isolated bacterium in pyoderma's.
Occasionally there will be mixed infections, and rarely, other
bacteria will predominate. Antibiotic selection may be empirical
(based on the clinicians preference and experience), or based on
culture and sensitivity results. Therapy, however, should always
include a beta-lactamase resistant antibiotic with known activity
against Staphylococci. Antibiotics fulfilling these criteria are
listed in Table 2. More specific antibiotics can be based on
sensitivity results especially in recurrent infections, deep pyoderma's,
non-responsive pyoderma's and immuno-incompetent patients. Cultures
from draining sinuses may yield non-pathogenic contaminants.
Cultures taken from intact pustules will give more accurate
sensitivity results. Antibiotic sensitivity results generally give a
good guide, but several strains of Staphylococcus may be present at
any one time giving different results. The strain cultured may not
be representative of the pathogen present. Furthermore, the
correlation between in vitro and in vivo performance of antibiotics
is not absolute. Sensitivity results must be interpreted in
conjunction with clinical symptoms, and other factors such as drug
costs, tolerance and availability. Furthermore, therapeutic failure
may be due to insufficient penetration into affected tissue.
Potentiated sulphonamides and ampicillin give mixed results and
amoxycillin and tetracyclines have generally given poor results.
Table 2 lists antibiotics which are useful in bacterial skin disease
in small animals. Fluoroquinolones (enrofloxacin, marbofloxacin and
orbifloxacin) are capable of good intracellular and intercellular
penetration and also a high activity within phagocytes. Antibiotics
can be divided into two groups, according to their pharmacodynamics;
those that work in a concentration-dependant fashion (e.g.
fluoroquinolones) and those which have a time dependant effect (e.g.
cephalosporins). The significance of this is that for
fluoroquinolones, efficacy is a function of peak plasma
concentration rather than half-life whereas for cephalosporins, the
duration of plasma and tissue concentration at high enough levels is
more important. Fluoroquinolones are most effective if given once
daily; and also, cephalosporins must be administered twice daily.
Dosages of systemic antibiotics useful in small animal
bacterial skin disease.
|Amoxycillin with clavulanic acid
||22 - 33
||5.5 - 11
||5 - 10
This is at least as important as the choice of antibiotic to be
used. The duration of therapy must be based on factors such as
patient age and weight, depth of infection, concurrent therapy, type
of infection (localised or generalised; superficial or deep) and
immunosuppressive factors. Surface and superficial pyoderma's need
10 days of therapy, whereas deep pyoderma's require 6 weeks or more.
For pyodemodicosis, GSD pyoderma, and in immunocompromised patients
treatment must be continued for a minimum of three weeks after what
appears to be clinical cure. Glucocorticoids suppress the
inflammation, reducing the blood supply at the site of infection and
also the hosts immune response. The skin will appear normal, but
will still be infected. Pet owners must be made aware that response
to therapy may take weeks and premature drug withdrawal will only
result in relapses, drug resistance, and extra costs. Some pet
owners are reluctant to administer an adequate course of
antibiotics. Re-assuring the pet owner of the safety of antibiotics,
especially in relation to the risks posed by not treating, is
central to successful control of bacterial skin disease.
Chronic recurrent pyoderma
This is a common and frustrating problem (Figure 9). These cases
require a review of the history, a thorough clinical examination and
a repeat of the laboratory tests. Withdrawal of all therapy at this
stage may be beneficial. There may be inappropriate concurrent
therapy, or long-term antibiotic therapy may have resulted in
antibiotic resistance. Searching for underlying causes (e.g. poor
nutrition, demodicosis, atopy, flea, food and/or other allergy),
while repeating culture and sensitivity regularly is necessary. Very
old or very young animals may be immuno-incompetent, as are those
with neoplastic disease or receiving immunosuppressive drug therapy.
It has been proposed that an absolute neutrophilia as well as a
lymphocyte count of at least 1000 cells/microlitre should be seen in
dogs with a bacterial pyoderma. If these two criteria are not met,
immuno-incompetence is suspected and underlying immunosuppressive
disease processes should be searched for.
Antibiotic resistance of S. intermedius, the bacterium involved in
small animal dermatology, is slow when compared to the rapid
development of resistance which occurs in man with S aureus.
However, high levels of resistance to penicillin G, ampicillin and
amoxycillin, and to the tetracyclines are common (25 - 70% in a
recent worldwide study). Resistance to trimethoprim and sulphonamide
combinations is about 5%. Resistance to synthetic penicillins such
as oxacillin, cloxacillin, and methicillin is uncommon.
Marbofloxacin, enrofloxacin, cephalexin and amoxy-clav also have
minimal resistance build-up. Where Gram-negative infections are
encountered, a drug effective against Staphylococcus is usually
sufficient except where Pseudomonas is involved.
Deep granulomatous pyoderma's may respond to anti-mycobacterial
therapy. Rifampicin is used for tuberculosis infections in man.
Resistance to this drug builds up rapidly and it does have some
hepatotoxicity. For these reasons short (two week) courses are used.
Covering antibiotics (e.g. cephalexin) are administered concurrently
to prevent the development of resistance.
Long term, low dose daily administration of antibiotics is not
advised due to the development of antibiotic resistance. Pulse
therapy, however, using the recommended dosage for one week a month
(or week on, week off) has allowed many pets to live a relatively
normal life. Cephalexin is advised in pulse therapy along with
regular re-examinations and strict ectoparasite control.
Several drugs, such as levamisole and cimetidine have been used in
an attempt to stimulate the immune system. These drugs are not
licensed for this use and there is little support in the literature.
The effect of autogenous vaccination is also not yet clear.
Bacterial products derived from Staphylococcus aureus phage lysate
and Propionibacterium acne are available commercially in some
countries. These are administered as adjunctive therapy in an
attempt to stimulate the immune system. Thorough treatment of acute
and superficial cases of bacterial skin infections with appropriate
products remains the most effective method of preventing development
of deep pyoderma's.
Successful therapy of pyoderma involves the identification and
elimination of underlying inciting causes combined with appropriate
antibacterial treatment. Systemic and topical antibacterial therapy
may be necessary as well as immunostimulation. In those cases where
the underlying causes cannot be identified and eliminated, prolonged
and repeated therapy may be necessary.
- Briggs O.M. 2001 Skin disease of the extremities. Part I
Vetmed 14: 5 - 10.
- Briggs O.M. 2001 Skin disease of the extremities. Part II
Vetmed 15: 5 - 8.
- Lloyd D 2002 Feline infectious dermatoses. In: Proceedings of
the 18th ESVD-ECVD Congress of Veterinary Dermatology pp 131 -
- Mason I. S. 2001 Antibiotic selection in practice. In:
Proceedings of the 17th ESVD-ECVD Congress of Veterinary
Dermatology pp 57 - 60.
Dr O M Briggs
BSc, BVSc, Msc(Med), FRCVS
Royal College of Veterinary surgeons recognised specialist in veterinary dermatology