Canine pyoderma: bacterial skin disease in dogs. Part 1

INTRODUCTION

Pyodermas are very common bacterial skininfections in dogs. The dictionary definition ofpyoderma is a skin infection causing thedevelopment of pus or pustules; however in dogs pusand pustules are often not evident or are entirelyabsent. In practice the presenting clinical signs arevariable and can mimic almost any otherdermatological disease, which can make thecondition difficult to diagnose.

The first of this series of two articles will outline thecommon pathogens, predisposing factors, clinicalsigns and diagnosis of the disease. Infections causedby mycobacteria and other ubiquitous soilsaprophytes, which are uncommon, will not bediscussed. The second article will outline thetreatments available and long-term management ofthe condition.

PATHOGENESIS

Skin and hair generally provide effective protectionagainst the physical, chemical and microbial insultswhich are encountered every day. The cutaneousmicroenvironment provides niches for small numbersof microorganisms, which are supported by host/microorganism interactions. When these interactionsare disrupted, microbial proliferation can occur,leading to breakdown of the physical andimmunological defences provided by the epidermalbarrier. In dogs, several other predisposing factorswhich contribute to a breakdown in the epidermalbarrier have been identified (see below).

Almost any bacterium can be involved in aninfection; however, the most common organismisolated from canine bacterial skin infections isStaphylococcus intermedius, recently renamedStaphylococcus pseudintermedius. These bacterialinfections may be either primary or secondary.Primary infections are those where no underlying orpredisposing conditions are identified and thereforeonly the infection needs treating. In secondarypyodermas, however, it is the underlying orpredisposing factors that are responsible for theinfection. So in these cases the successful long-termresolution of the infection is generally dependent onidentifying and managing the underlying orpredisposing factors, as well as the infection itself.

BACTERIA

The bacteria isolated from skin are classified asresident (those that live on the skin andmucocutaneous sites) or transient (those that are notnormally able to survive on the skin for any length oftime, but can do so if abnormal cutaneousenvironmental conditions are present). All bacteriacolonise the skin by adhering to corneocytes.Adherence results from adhesins (surface moleculeson the bacteria) binding to receptors on thekeratinocytes. The bacteria produce toxins, enzymesand other factors that modify the cutaneousmicroenvironment and which may cause abreakdown in the epidermal barrier, leading toinfection. The organisms of major interest in caninedermatology are discussed below.

Staphylococci

Staphylococcus pseudintermedius

Staphylococcus pseudintermedius is frequently isolatedfrom mucocutaneous sites, where it is considered tobe resident. It can be transferred from these sites toskin and distal hairs during grooming, and inparticular to pruritic areas, where they may cause orcontribute to pyodermas. It is normally considered atransient organism.

Staphylococcus aureus

Staphylococcus aureus is a well-known humanpathogen that is being isolated more and more fromcanine samples. It is of major interest because of theincreasing number of meticillin resistant infections indomestic animals. S. aureus is thought to betransmitted to dogs from in-contact human carriers.Nasal carriage of the bacterium in health-careworkers, chronically ill patients and those receivingimmunosuppressive disease has been implicated.Dogs with an existing breakdown in the epidermalbarrier may be more susceptible to colonisation andconsequent infections.

Staphylococcus schleiferi

Staphylococcus schleiferi is becoming recognised as apathogen in both people and dogs. It has beenisolated from dogs with otitis externa and recurrentpyoderma. S. schleiferi subspecies coagulans has verysimilar biochemical properties to those of S.pseudintermedius. Some S. schleiferi strains are meticillinresistant and possess the mecA gene.

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Anita Patel BVM, DVD, MRCVS RCVS Recognised Specialist in Veterinary DermatologyDERMATOLOGY REFERRALS, 23 SEARCHWOOD ROAD, WARLINGHAM, SURREY. CR6 9BB

Canine pyoderma: bacterial skindisease in dogs. Part 1

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Pseudomonas aeruginosa

This Gram -ve rod-shaped organism is a commoncause of both otitis externa and otitis media. It is alsosometimes isolated from the lesions of deeppyoderma in dogs. Recently it has also been reportedas a primary pathogen in dogs with the clinical signsof both superficial and deep pyoderma. It is normallya transient organism that can colonise skin wherethere is a breach in the epidermal barrier.

Other bacteria

Both E. coli and Proteus spp. are opportunisticorganisms that take advantage of existing skindisease to complicate the condition. They tend tobe involved mainly in deep pyoderma and otitisexterna. They are also occasionally isolated fromdogs with fold dermatitis, especially on the lipfolds and interdigital skin.

PREDISPOSING FACTORS

Breed

Although bacterial infections can occur in any dog,some breeds are predisposed to contract them. Theyinclude Bull Terriers, German Shepherd Dogs,Boxers and Doberman Pinschers. Studies in BullTerriers have shown an increase in in vitrostaphylococcal adherence to their keratinocytescompared with those from other breeds.

Anatomy

The microenvironment of the skin surface varieswith the anatomical site. It depends on a number oflocal factors such as humidity, occlusion (such as inskin folds and interdigital skin) and the length anddensity of the coat. Areas of increased humidity, withpoor air circulation, allow bacterial proliferation andsubsequent colonisation; so dogs with excessive skinfolds are predisposed to surface colonisation.

Immune status

Innate and acquired immunity in the skin provideprotection against a variety of cutaneous pathogens,including bacteria. Primary immune deficiencies area predisposing factor, e.g. canine granulocytopathy

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syndrome in Irish Setters and German Shepherddeep pyoderma. Immunosuppressive drugs, such ascorticosteroids or ciclosporin, and internal diseases,such as spontaneous and iatrogenic hyper-adrenocorticism, are also common predisposingfactors.

Hypersensitivity

Hypersensitivity to environmental, insect and foodantigens is known to cause inflammatory skindisease. An inappropriate immunological response tothe antigen results in a general or localisedbreakdown in the epidermal barrier, allowingcolonisation by pathogenic bacteria.

Ectoparasites

Demodex mites are often associated with bothsuperficial and deep pyoderma. An altered follicularmicroenvironment and immune-dysregulation arelikely to be the predisposing factors in these cases.

Environment

Increases in both ambient temperature and humiditycan lead to changes at the surface of the skin, whichcan favour microbial proliferation.

Trauma

Any injury to the skin such as bites, cuts, abrasionsand bruising, can result in infection.

CLINICAL SIGNS

Pyoderma is classified according to the depth of theinfection, as surface, superficial or deep. Thisclassification is not dependent on the pathogenicorganism responsible.

The spectrum of clinical signs seen in pyoderma casesis wide. Lesions in surface and superficial infectionsinclude erythema, papules, pustules, epidermalcollarettes, scaling, crusting, hyperpigmentation,lichenification, alopecia and excoriations; lesions indeeper infection also include ulceration, drainingsinuses and furuncles. It is important to note thatsome dogs can have overlapping syndromes. Table 1summarises the various syndromes.



TABLE 1: Canine Pyoderma: Classification, syndromes, clinical signs and predispositions

Depth ofInfectionSurface

Superficial

Syndrome

Intertrigo (skin fold

dermatitis): sub-

classified according to

the site affected, e.g.

nasal fold, facial fold, lip

fold, vulval fold, tail fold

and body fold (Fig. 1)

Pyotraumatic

dermatitis (acute moist

dermatitis)

(Fig. 2)

Impetigo

Superficial spreading

pyoderma and

folliculitis

(Figs. 3 and 4)

Mucocutaneous

pyoderma

(Fig. 5)

Bacterial overgrowth

syndrome (Fig. 6)

Predominant Clinical Signs

Erythema, crusting, scaling,

hyperpigmentation, lichenification, erosions

Variable pruritus and malodour

Acute onset of circumscribed moist area of

erythema, exudation, erosion and alopecia

Sharp demarcation between affected and

unaffected skin

Severe pruritus

Non-follicular papules and pustules on non-

haired skin and crusts

Usually located on ventral abdomen and

inguinal regions

Usually non-pruritic

Superficial spreading pyoderma: epidermal

collarettes, hyperpigmentation, erythema,

alopecia, and seborrhoea

Pustules not usually evident

Superficial folliculitis: follicular papules,

pustules, comedones, scaling and crusting

Type of lesion depends on coat length and

density: raised tufts of hair (and with

chronicity multifocal patches of alopecia)

may be the only sign in short-coated breeds

such as Boxers and Rhodesian ridgebacks;

follicular casting, scaling and clumping of hair

tend to be features in long-coated dogs

Distribution of lesions depends on

predisposing cause

Erythema, exudation and crusting

Depigmentation and fissuring of affected

sites in chronic cases

Usually affects nose and lips but occasionally

seen on other

mucocutaneous sites

Erythema, lichenification,

hyperpigmentation, excoriations and

alopecia

Intense pruritus

Predisposing Factors

Friction between skin folds

Poor ventilation

Increased moisture (tears, saliva or

urine)

Obesity

Self trauma due to impacted anal

sacs, otitis, flea bites, etc.

Increased humidity and temperature

Underlying hypersensitivity

Endoparasites

Unhygienic environments

Poor nutrition

Viral diseases

Large flaccid pustules seen in older

dogs with endocrine diseases

Atopic dermatitis

Adverse food reactions

Flea allergic dermatitis

Ectoparasitic infestations

Poor hygiene

Endocrine disorders

Local trauma



Predisposed Breeds

English Bulldogs,

Pugs, Pekingese,

Boston Terriers and

Chinese Shar Pei

Golden Retrievers,

Labradors, German

Shepherd Dogs,

Collies

Young dogs of any

breed around

puberty

Any breed

Any breed but

especially German

Shepherd Dogs and

their crosses

Any breed


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TABLE 1: Canine Pyoderma: Classification, syndromes, clinical signs and predispositions continued

Depth ofInfection

Syndrome Predominant Clinical Signs Predisposing FactorsPredisposed Breeds

Deeplocalisedpyoderma

Deepgeneralisedpyoderma

Subcutaneousabscesses

Nasal, chin, muzzle,

pedal

(Figs. 7 and 8)

Pyotraumatic folliculitis

and furunculosis

Acral lick furunculosis

Deep folliculitis,

furunculosis and

cellulitis

German shepherd dog

deep pyoderma (Figs.

9a and b)

Bacterial

pseudomycetoma

Lesions are localised at affected sites

Clusters of papules, draining sinuses,

erythema, swelling, furuncles,

hyperpigmentation, haemopurulent exudate

Usually localised plaque-like lesion with

surface exudation and alopecia

Satellite lesions consisting of papules,

follicular papules, erythema, exudation,

alopecia and occasional furunculosis

Lesion differentiated from pyotraumatic

dermatitis by presence of papules and the

lesions are not well demarcated

Solitary, firm, raised alopecic lesion that is

ulcerated or eroded in the centre and

hyperpigmented on the periphery

Usually seen on the anterior aspect of distal

limb

Clusters of papules, ulceration, draining

sinuses, haemopurulent exudate, furuncles,

oedema, hyperpigmentation, and erythema

Pruritus and pain variable

Clusters of papules, draining sinuses,

haemopurulent exudate, furuncles,

ulceration, hyperpigmentation, crusts and

alopecia

Lesions usually found on trunk and often not

totally visible until the hair is clipped

Solitary or multiple nodules with draining

fistulae and purulent exudate

Type of exudate depends on organism

involved

Genetic predisposition


Demodicosis

Hypersensitivity

Boredom

Lack of exercise

Underlying pain due to arthritis

Hypersensitivity

Hypothyroidism

Demodicosis

Hypersensitivity

Immunosuppression due to drugs,

hyperadrenocorticism

Foreign bodies

Acquired cell-mediated

immunodeficiency

Allergic skin disease

Endocrine disorders

Trauma

Nasal pyoderma:

German Shepherd

Dogs, Collies, Bull

Terriers, Pointers

predisposed

Muzzle and chin

deep pyoderma:

short-coated dogs

Pedal pyoderma: can

occur in any breed,

but English Bulldogs,

Bull Terriers, Great

Danes, Bassett

hounds over

represented

Golden Retrievers,

Labradors, Saint

Bernards,

Newfoundlands

Large dogs

Any breed

Affects middle-aged

to old German

Shepherd Dogs

Any breed



Fig. 1: Nasal fold dermatitis in an English Bulldog.

Fig. 2: Pyotraumatic dermatitis (acute moistdermatitis) on a German Shepherd Dog.

Fig. 3: Superficial folliculitis on a dog withhyperadrenocorticism.

Fig. 4: Superficial folliculitis seen as a patchy alopeciaand scaling in a short-hair dog.

Fig. 5: Mucocutaneous pyoderma in a GermanShepherd Dog.

Fig. 6: Bacterial overgrowth syndrome in an atopicLabrador.

Fig. 7: Chin pyoderma in a Doberman.

Fig. 8: Draining sinus in a dog with deep pedalpyoderma secondary to demodicosis.


DIAGNOSIS

Differential diagnosis

The differential diagnoses depend on thepredominant clinical signs at the time ofpresentation. It is also worth remembering thatseveral syndromes may be seen in the same animal.

Papules, pustules and pustular crusts ● superficial spreading pyoderma● superficial folliculitis● impetigo● pemphigus foliaceus ● demodicosis.

Alopecia, follicular papules and scaling ● superficial folliculitis ● dermatophytosis ● demodicosis ● urticaria.

Hyperpigmentation, lichenification, crusting

and erythema ● Malassezia dermatitis ● bacterial overgrowth syndrome ● demodicosis. Draining sinuses, haemorrhagic bulla, exudate,

hyperpigmentation and oedema ● deep pyoderma ● demodicosis ● dermatophytosis ● mycobacterial infections ● sterile idiopathic nodular panniculitis ● sterile pyogranulomatous dermatitis ● eosinophilic furunculosis.

Diagnostic tests

Cytology

Depending on the type of lesions present, thequickest, easiest and cheapest first line test is in-house cytology.

Impression smears: useful for exudative lesions,papules and pustules. Tape strips can be used toobtain an impression of the skin surface. Neutrophilsand intracellular bacteria are the predominantfindings in superficial and surface pyoderma.Numerous extracellular bacteria are evident inbacterial overgrowth syndrome (Fig. 10).Macrophages, neutrophils and lymphocytes arefound in pyogranulomatous inflammation (Fig. 11)which tends to suggest deeper infection.

Fine needle aspirates: These are useful for nodules and subcutaneous abscesses where materialfrom the core can be obtained for cytologicalexamination.

Culture and sensitivity

Although not routinely done for superficial andsurface infections, culture and sensitivity testingshould be performed in the following situations: ● deep pyoderma ● recurrent superficial or surface pyoderma ● rod-shaped organisms found on cytological

examination ● empirical treatment fails to give expected result● animal is immunosuppressed● if there is a possibility that someone in the

household may be ill, health-care worker, etc.

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Fig. 9a: German Shepherd Dog deep pyoderma in amiddle-aged dog.

Fig. 10: Large numbers of coccoid bacteria on a tapestrip preparation from a dog with bacterialovergrowth syndrome.

Fig. 11: Foamy macrophages and neutrophilsconsistent with pyogranulomatous inflammation.

Fig. 9b: Close up view of the same dog showingdraining sinuses, purulent exudate, hyperpigmentationand ulceration.


Swab samples are useful for surface and superficialinfections and biopsy sample for tissue culture isrecommended for deep infections.

Biopsy

A biopsy is not necessary to make a diagnosis of apyoderma; however, histological changes consistentwith both superficial and deep infections can be seenon biopsies. Papules, intact pustules, nodules orbullae are ideal lesions to biopsy, in order to rule outother diagnoses. The histological changes vary withthe depth of the infection. Inflammatory changes insuperficial infections are generally confined to theepidermis and the upper portion of the hair follicle;and the inflammatory infiltrate is mainlyneutrophilic. In deep folliculitis and furunculosis theinflammatory changes occur deeper in the hairfollicle and deep dermis, because of hair folliclerupture. The inflammatory cells are mainlyneutrophils and macrophages with varying numbersof eosinophils, lymphocytes and plasma cells.

FURTHER READING

CHESNEY, C. J. (1997) The microclimate of the canine coat: the effects

of heating on coat and skin temperature and relative humidity.

Veterinary Dermatology 8(3):183-90.

HARVEY, R. G. and LLOYD, D. H. (1994) The distribution of

Staphylococcus intermedius and coagulase-negative staphylococci in the

hair, skin surface, within the hair follicles and on the mucous

membranes of dogs. Veterinary Dermatology 5(2):75-81.

HARVEY, R. G. and LLOYD, D. H. (1995) The distribution of bacteria

(other than staphylococci and Propionibacterium acnes) on hair, at the

skin surface and within hair follicles of dogs. Veterinary Dermatology

6(2):79-84.

LLOYD, D. H., ALLAKER, R. P. and PATTISON, A. (1991) Carriage of

Staphylococcus intermedius on the ventral abdomen of clinically normal

dogs and those with pyoderma. Veterinary Dermatology 2(3-4):161-4.

MASON, I. S., MASON, K. V. and LLOYD, D. H. (1996) A review of the

biology of canine skin with respect to the commensals Staphylococcus

intermedius, Demodex canis and Malassezia pachydermatis. Veterinary

Dermatology 7(3):119-32.

MCEWAN, N. A. (2000) Adherence by Staphylococcus intermedius to

canine keratinocytes in atopic dermatitis. Research in Veterinary

Science 68(3):279-83.

PIN, D., CARLOTTI, D. N., JASMIN, P., et al. (2006) Prospective study

of bacterial overgrowth syndrome in eight dogs. Veterinary Record

158(13):437-41.

SASAKI, T., KIKUCHI, K., TANAKA, Y., et al. (2007) Reclassification of

phenotypically identified Staphylococcus intermedius strains. Journal of

Clinical Microbiology 45(9):2770-78.

SCOTT, D. W., MILLER, W. H. and GRIFFIN, C. E. (2001) Muller and

Kirk’s Small Animal Dermatology, 6th edn., pp. 274-335. WB Saunders,

Philadelphia.


C O N T I N U I N G P RO F E S S I O N A LD E v E L O P m E N T S P O N S O R E D B YB AY E R A N I m A L H E A LT H

1. Which of these statements is untrue:

a. The predominant lesions in bacterial skin

infections are pustules and pus.

b. The lesions are variable and the spectrum

includes papules, pustules, epidermal collarettes,

erythema, crusting, scaling, hyperpigmentation,

lichenification and ulceration.

c. Bacterial infections occur concurrently with

almost any skin condition.

d. Bacterial infections are classified according to the

depth of infection.

2. Which of the following differential diagnoses would

you consider in a dog presented with severe

hyperpigmentation, erythema, lichenification and

alopecia:

a. Malasseziosis

b. Bacterial overgrowth syndrome

c. Superficial folliculitis

d. Demodicosis

e. All of the above

3. Which of the following statements is most likely to

represent deep infection:

a. Neutrophils are the only cell present on an

impression smear.

b. Macrophages, neutrophils and lymphocytes are

present on an impression smear or fine needle

aspirate.

c. Lymphocytes are the predominant cells on

smears.

d. All of the above

These multiple choice questions are based on the abovetext. Answers appear on page 75.


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Canine pyoderma: bacterial skin disease in dogs. Part 1