Bacterial skin disease Flashcards
What is the role of normal cutaneous microbial flora?
Can aid exclusion of pathogens, but can also contribute to disease
Define the following terms:
a: resident
b: nomad
c: transient
d: pathogen
a: Can replicate on skin and persist
b: organisms that can colonise and reproduce on skin for short times
c: cannot replicate so only stay for short time
d: organisms that become established and can proliferate on the skin surface and deeper, that are deleterious to normal physiology of teh skin
What is required in order for microorganisms to cause skin disease?
Skin’s barrier function must be compromised i.e. primary disease leading to secondary infection by resident and transient organisms
What are the innate skin defences?
- Squames: shed from top layer, leading to shedding of microorganisms
- Sebaceous glands
What are the specific defences in the skin?
Langhan’s cells in the dermis
What is the usual result of chemical, physical or microbiological insult on the skin?
Usually leads to increased turnover of skin and increased activity of the sebacious glands, leading to scaliness and dry or wet seborrhaeic skin
- Increased sebum leads to smell
Give examples of primary disease that may allow bacterial skin disease to occur
- Any disease that affects the defences
- Atopic dermatitis
- Endocrinopathy
- Nutritional deficiencies
- trauma/overcrowding
- Environmental damage
What are the 3 types of pyoderma called?
- Surface
- Superficial
- Deep
What are the 2 forms of surface pyoderma?
- Acute moist dermaittis (“wet eczema”)
- Skin fold pyoderma (“intertrigo”)
What is surface pyoderma?
Secondary bacterial colonisation of skin surface
Describe the presentation of acute moist dermatitis
0 Aka hot spot, pyotraumatic dermatis
- Very acute onset (overnight)
- Intensely pruritic and painful
- Alopecia, exudative, erythematous
Outline the underlying causes of acute moist dermatitis
Primary pruritic conditions e.g. otitis externa, anal gland impaction, fleas/other ectoparasites, function of hair coat, breed predisposition (golden retriever)
Explain why dogs with thick undercoats may be predisposed to acute moist dermatitis
- Thick undercoat on hot days means skin gets very hot
- Develop pruritus which leads to formation of acute dermatitis lesion very quickly
Where does intertrigo commonly occur?
- Facial folds in brachys
- Vulval fold (spayed with deep-set vulva)
- Lip fold (some spaniel breeds, can be considerable cause of halitosis)
- Tail fold (deep set tails, esp, brachys)
How is surface pyoderma diagnosed?
- Dermatological signs main method
- may do bacterial culture and susceptibility testing, skin biopsies (histo +/- culture)
What is superficial pyoderma?
Infection involving skin and hair follicle epithelium
What are the 4 types of superficial pyoderma?
- Impetigo
- Superficial bacterial folliculitis
- Pyotraumatic folliculitis
- Mucocutoaneous pyoderma
Describe the occurrence of impetigo
- Common, often recurrent (secondary) e.g. allergy/endocrinopathy, parasites
- Often diffuse, ventral abdomen especially
Describe the appearance of impetigo
- Pustules: hair in centre i.e. folliculitis
- Papules
- Epidermal collarettes
- Alopecia
- Variable pruritus: more if inflam/allergic, less if endocrinopathic
What is canine deep pyoderma?
Infection involving the dermis and subcutaneous tissue
What are the 3 types of canine deep pyoderma?
- Cellulitis (diffuse condition)
- Furunculosis (hard lesions and discharge to surface)
- Acral lick furunculosis
Compare furunculosis and cellulitis
- Furuculosis: “boil”, follicle infection spreads into dermis
- Cellulitis: infection of follicles and surrounding dermis
What breed is predisposed to deep pyoderma and why?
GSD: immunodeficiency in some lines of GSD breed, impaired barrier function of skin
Describe the appearance of deep pyoderma
- Papules
- Pustules
- Alopecia
- Nodules (furuncles, palpable lumps in dermis)
- Sinuses
- Draining tracts
Describe the clinical signs of cat bite abscesses
- Acute onset
- Pyrexia
- Painful
- Inappetance, depression
- Fluctuant swelling (often head/back end)
- Scab +/- puncture wounds
What aerobes are commonly involved in cat bite abscesses?
- Pasteurella spp
- Actinomyces spp
- Nocardia spp
- Staphylococcus spp
- Rhodococcus sp
- Enterobacteriaceae
- Streptococcus
What anaerobes are commonly involved in cat bite abscesses?
- Porphyromonas spp
- Fusobacterium
- Peptostreptococcus spp
- Clostridium spp
When is culture and sensitivity required for abscesses?
Only if recurrent
Compare rabbit and cat abscesses
- Cat bite abscess pus thin, drains easily
- Very thick in rabbits, does not drain and lancing and flushing alone often ineffective, usually require complete surgical excision
Other than bacteria, what else may cat bite abscesses be a source of?
Viral infections e.g. FIV
For a rabbit abscess where surgical excision is not possible, what other treatments are available?
- e.g. a jaw abscess
- Aggressive debridement
- removal of affected teeth and bone
- Marsupilisation
- Systemic antibiotics required
- Euthanasia (very difficult to treat)
- Adjunctive treatments e.g. honey, sugar solutions, AIPMMA-beads, calcium hydroxide
What is meant by marsupiliation?
Remaining abscess capsule suture to skin to allow topical therapy on remaining abscess tissue
Where are abscesses most common in large animals and what is a key differential?
- Umbilical, esp. in young stock
- Umbilical hernias are a key differential
How can umbilical hernias be differentiated from umbilical abscesses?
- Hernias are soft and should reduce on palpation
- Abscesses are more likely to be firm
What is a common complication that may occur with umbilical abscesses in large animals?
May erode through abomasal wall, but are easily stitched up and tend to do well
List non-bacterial differentials for “bacterial” type presentations
- Anal furunculosis
- Juvenile cellulitis (aka puppy strangles)
- Are autoimmune conditions
What is anal furunculosis?
Sinuses that track through skin around anus, occasionally may affect inside back of legs. Are not fistulas
Where does anal furunculosis occur?
Near anal sacs, but do not connect with them, rectum or colon
What are the clinical signs of anal furunculosis?
- Open areas of ulceration
- Become very tail shy
- Lick and bite at affected region
- Pain
- Difficulty straining on defaecation
What breed is predisposed to anal furunculosis?
GSD
What is the cause of anal furunculosis?
Unknown, not bacterial (may be secondary infection), tail carriage suggested as a cause
What causes juvenile cellulitis?
Not bacterial, may be immunological
Describe the appearance and clinical signs of juvenile cellulitis
- Typically face
- Alopecic inflamed lesions with oedema
- Papules, pustules and crusts
- Often affects perioral, periocular, chin, muzzle and ears
- Significant sub-mandibular lymphadenopathy
- Lethargy, fever and anorexia in some, joint pain in others
Describe the nature of aspirates taken from lymph nodes in a dog with juvenile cellulitis
Suppurative lymphadenitis with many neutrophils without bacteria
What is the diagnostic importance of primary dermatological lesions?
Usually most obvious in early stages of the disease and are those upon which a definitive diagnosis should be based
What is the diagnostic importance of secondary dermatological lesions?
- Mostly non-specific and caused by pathological changes resulting from primary disease and related lesions
- Not as valuable for diagnosis
How is canine superficial pyoderma diagnosed?
- Based mainly on dermatological signs
- May do bacterial culture and susceptibility testing
- Skin biopsy (histology +/- culture) if recurrent to look for underlying skin disease rather than diagnosis of pyoderma
How is canine deep pyoderma diagnosed?
- Dermatological signs
- Cytology (aspirate/impression smear)
- Bacterial culture and susceptibility testing (systemic antimicrobials required for long periods)
- May also do skin biopsies (histology +/- culture)
How is anal furunculosis diagnosed?
- Physical examination
- Rule out other causes
What is the function of an abscess?
- Defensive reaction to tissue to prevent the spread of infectious material (granulation tissue)
- Barrier may prevent immune cells from attacking bacteria in the pus
Compare abscesses and emphyaemas
Emphyaema is an accumulation of pus in pre-existing rather than newly formed anatomical cavity
What is an important differential for a lesion that looks like deep pyoderma on a paw?
Need to rule out abscess secondary to a foreign body
Describe the typical treatment and management approach to an abscess
- Sedate/GA, analgesia
- +/- systemic antibacterials
- Clip and prep, local anaesthetic
- Lance abscess, drain and lavage
- Leave open
- If large, insert drain/marsupialise
- may need to continue systemic antibacterials depending on degree of abscess, systemic signs and practice policy
What factors need to be addressed in the treatment of canine surface pyoderma?
- The primary disease
- The bacterial infection
- THe inflammation
Describe the treatment of the primary disease in canine surface pyoderma
- Identify cause
- Skinfolds: surgical resection possible if required, or regular cleaning with anti-bacterial wipes
- Consider fleas/ears/other allergens
Describe the treatment of the bacterial infection in canine surface pyoderma
- Use anti-staphylococcal antibacterials
- IN order of choice:
- 1: clindamycin, lincosamides/macrolides
- 2: amoxycillin clavulanate
- 3: TMPS (cheap, but resistance an issue, hard to get)
- 4: Cefalexin (20-25mg/kg BID) or quinolones (C+S only if no alternative), last resort only if long standing deeper pyoderma non-responsive to linco/macrolides
- If non-responsive to amoxy-cav/cefalexin, suggests beta-lactam resistance
Describe the treatment cascade for the bacterial infection in superficial pyoderma in a cat
- 1: Amoxyclav
- 2: Clindamycin
- 3: Cefalexin
What treatment is most commonly used to treat the inflammation in surface pyoderma?
- Usually corticosteroid, often topical antibacterial + corticosteroid e.g. Isaderm (fusidic acid + betamethasone)
- Fuciderm gel and surolan ear drops also licensed
- Easy, as is a surface disease
- Glucocorticoid injection may be required to allow handling as is very painful condition
What is the antibiotic protocol used in the treatment of superficial pyoderma?
- Systemic anti-staphylococcal antimicrobial
- Minimum 3 weeks + 1 week beyond cure
Other than antibacterials, what else is required in the treatment of canine superficial pyoderma?
Manage underlying cause e.g. flea management
Outline the use of antibacterial shampoos/rinses in the treatment of canine superficial pyoderm
- Long term maintenance
- Physically reduces microbial population
- Reduces levels of microbial by-products
- Removes debris/discharge
- Allows active agent to reach site of action
- Soothing
- Surface grease/debris may adversely affect activity of therapies
- Keeps owner aware of therapy and involved with condition
- E.g. malaseb shampoo, pacutol shampoo, seleen
Describe the use of topical antibacterials (not shampoos) in the treatment of canine superficial pyoderma
- Many available, most unlicensed
- Chlorhexidine, ethyl lactate, benzoyl peroxide, piroctone olamine, selenium sulphide
- Most effective treatments tend to contain chlorhexidine
Describe the systemic antibacterial protocol used in the treatment of canine deep pyoderma
- Long course of systemic antibiotics
- Based on culture and sensitivity
- NOT clindamycin (only bacteriostatic)
- Minimum 6 weeks + 2 weeks beyond cure
- Must be anti-staphylococcal
Describe the treatment of canine deep pyoderma
- Treat primary cause
- Topical antibacterial shampoo/rinse
- Long courses of systemic antibacterials
- Discuss with owner re. risk of recurrence, management difficult
What is the long term management required for canine deep pyoderma?
- Intermittent pulses of antibacterial treatment e.g. 2 days on, 5 days off, or 1 week on, 2 weeks off
- Immunostimulants e.g. staphage lysate (SPL), sterile staphylococcal vaccine, discussion with dermatologist re. management of recurrent deep pyoderma
Explain the use of staphylococcal vaccines in the treatment of canine deep pyoderma
- Vaccine contains components of S. aureus, bacteriophage and some culture medium ingredients in solution
- Induces cell mediated immunity
Describe the treatment of anal furunculosis
- Often recurs
- Cyclosporin most used as is immune mediated condition, responds well
- Radical surgery where all tissue removed
- Cryosurgery (apply freezing nitrogen)
- Radical and cryo less common and result in very painful patient
Outline the treatment used for juvenile cellulitis
- Corticosteroids (immunosuppress, often respond well)
- Usually cover with antimicrobials
What does MRSA stand for?
Methicillin resistant Staphylococcus aureus
What is the significance of MRSA regarding the treatment of canine pyoderma?
MRSA is resitant to all beta-lactams; cefalexin is often used in the treatment of canine pyoderma, but this will not be effective against MRSA
List the possible sources of MRSA in dogs
- Human
- Other dogs/animals
- Hospital (nosocomial infection)
- Pigs
How should suspected MRSA pyoderma cases be handled in a practice/hospital situation?
- Known/suspected cases taken immediately into consulting room to avoid contamination of waiting area
- Reduce movement of contaminated animals around pracice
- Cover discharging wounds
- Limit staff contact
- Isolate form healthy patients
- Barrier precautions e.g. wearing gloves
- Bathe in chlorhexidine to reduce cutaneous carriage
What advice should be given to the owners of patients infected with MRSA (or other bacterial skin infections)?
- Handwashing and disinfection important
- Discourage hospital visits
- If live with/are immunocompromised must seek medical advice
- Limit contact with other pets
- Set up isolated areas in home
- Wash bedding and disinfect home
Describe the appearance of dermatophilosis skin infection
- Exudative dermatitis with scab formation
- Paint brush leasions
- Scale
- Site determined by predisposition i.e. dorsum (rain run off, rain scald), feet/lower limd (underfoot conditions), clipping/shearing, ectoparasites
What is the most common species of dermatophilus? What are the most frequent hosts?
- Dermatophilus congolensis
- Wide host range, but most common are cattle, sheep, goats and horses (rare in pigs, dogs and cats)
Give alternative names for dermatophilosis
- Horse: Mud fever, scratches, dew poisoning
- Cattle, goats, horses: cutaneous streptothrochosis
- Sheep: lumpy wool (if wooled areas affected)
Describe the Dermatophilus organism
- Actinomycete
- Gram +ve filamentous bacterium
- Non-acid fast
What is required for initial infection with Dermatophilus to occur?
At least superficial skin damage, and activation of motile zoospore stage to form a mycelium
Where is dermatophilus found in the skin?
Confined to the epidermis
What are the 2 characteristic forms of dermatophilus?
- Filamentous hyphae
- Motile zoospores
Describe the pathogenesis of dermatophilus
- Zoospore attracted to by respiratory efflux of low levels of CA2 from the skin to susceptible areas on skin surface
- Zoospore can remain dormant in skin debris and scabs for many months in dry conditions
- Activate and germinate to produce hyphae which penetrate into living epidermis and subsequently spread in all directions from initial focus
- Penetration causes acute inflammatory reaction
Describe acute infection with dermatophilus
- Filamentous infavion of epidermid ceases in 2-3 weeks
- Lesions heal spontaneously
Describe how chronic infection with dermatophilus may develop
Affected hair follicles and scabs are sites from which intermittent invasions of non-infected hair follicles and epidermis occur
What agent causes caseous lymphadenitis and what species are affected?
- Corynebacterium pseudotuberculosis
- Sheep and goats
Describe the signs of caseous lymphadeitis
- Lesions take weeks to develop
- Swollen LN draining head and lungs
In what cells does Corynebacterium pseudotuberculosis survive?
Macrophages
What are the main bacterial skin infections in pigs?
- Exudative dermatitis caused by Staphylococcus hyicus
- Erysipelas caused by Erysipelothrix rhusiopathiae
Describe mycobacteria as a cause of skin TB in cattle
- Many species identified incl. bovis, microti, avium
- Common in cats
- Occurs due to environmental and wound contamination e.g from hunted small animals
- No evidence of zoonotic transmission (but may be reverse zoonosis)
Outline a logical diagnostic approach to a chronic, non-healing wound
- In any chronic, non-healing wound need to consider MRSA
- Swab for C+S
- Sensitivity may be specific to hospital
- Cover wound and barrier nurse or isolate patient
- Maintain basic hygiene
- Stop antibiotics as soon as granulation tissue present
- when sending sample to lab, notify concerns over MRSA/MRSP in order to optimise chance or organisms being detected
Outline the diagnostic approach to dermatophilosis
- Clinical signs and lesions
- Examination of fresh crusts and or impression smears of underside of fresh lesions
- Giemsa or DiffQuik staining
- Histology
- Culture and identification
- In chronic/recurrent infections use skin biopsies for histology +/- culture
Outline the diagnostic approach to caseous lymphadenitis
- Clinical exam
- Serological testing
- Bacterial culture and susceptibility testing (chronic/recurrent)
- Skin biopsies for histo +/- culture (chronic/recurrent)
Describe the clinical signs of greasy pig disease
- Dark, localised areas of grease and scale
- Excess sebum (smell)
- May become generalised due to stress (more common in piglets, weaners or gilt litters)
- If severe, skin turns black due to necrosis and pigs die
- Systemic illness due to toxin release causing liver/kidney damage
What are the potential primary causes of greasy pig disease?
- Damage (teeth, floors)
- Abrasions from concrete surfaces, metal floors, troughs, side panels
- Faulty procedures for iron injections, teeth/nail removal
- Fighting and skin trauma at weaning
- Mange giving rise to skin disease
- Damage to face by metal feeding troughs
- Abnormal behaviour (tail biting, ear biting, navel sucking, flank biting)
How is greasy pig disease diagnosed?
- Dermatological signs
- Bacterial culture and susceptibility testing
What are the clinical signs of erysipelas?
- Sudden death
- Very high temperature
- Sick pigs
- Skin lesions
- Lameness
- Reproductive failure
What are the clinical signs of feline skin TB?
- Granulomatous disease
- Mainly in skin (lumps)
- May be in lymph nodes, occasionally lungs or GI
How is feline skin TB diagnosed?
- Dermatological signs
- Skin biopsies (histology +/- culture)
- Bacterial culture and susceptibility; with high index of suspicion use ZN stain
Outline the management procedures for MRSA/MRSP skin infections
- Hygiene crucial
- Maximise topical therapy where possible, esp. chlorhexidine (2-4%) washes
- Be aware affected animals/in-contacts can be carriers after resolution of clinica disease
- Address underlying cause of infection to reduce risk of recurrence
Outline the management for dermatophilosis
- No treatment needed, often heal rapidly and spontaneously
- Manage skin problem e.g. flies, rain etc.
- Susceptible to a wide range of antimicrobials
- Short course usually enough
- Soak and remove crusts
- Topical antibacterials e.g. chlorhex, benzoylperoxide
List the antimicrobials that are effective against dermatophilosis
- Erythromycin
- Penicillin G
- Ampicillin
- Amoxicillin
- Tetracyclines
