Microbial skin disease Flashcards
Bacterial, fungal, viral and protozoal skin disease
Outline the management of caseous lymphadenitis
Remove positive individuals
Outline the management of greasy pig disease
- Treat with systemic antibiotics
- Topical antibacterial wash
- Fluids (to treat toxic liver/kidney damage)
Which antibiotics are effective against greasy pig disease?
Sensitive to most antibacterials, incl. penicillins
Outline the management of erysipelas
- Penicillin treatment
- Vaccine available
Describe the management of feline skin TB
- Excision
- Consider zoonotic potential
- Antimicrobials: combinations in an initial and a continuation phase
- In cases where resistance develops, may use traditional combination of rifampicin-isoniazid-ethambutol combination
Describe the initial phase of antimicrobial treatment for feline skin TB
- Usually requires at least 3 drugs for 2 months
- Initial phase commonly uses rifampicin-fluoroquinolone-clarithromycin/azithromycin
Describe the continuation phase of antimicrobial treatment for feline skin TB
- Usually requires 2 drugs and lasts for 4 months
- Usually uses rifampicin + either fluoroquinolone or clarithromyxin/azithromycin
Discuss the zoonotic risk of MRSA/MRSP
- 1 in 3 people colonised but unaffected
- Spread by direct contact, can be limited by basic hygiene
- MRSP more easily contracted by dogs than MRSA, and likely poses less zoonotic risk
- MRSP less antibiotic suscpetibility vs MRSA
What are risk factors that may predispose to nosocomial infections?
- Antibiotic overuse
- Antibiotic misuse (esp. not completing course)
- Hospitalisation (duration)
- Patient’s disease status, age
- Number of diagnostic or therapeutic procedures
What are the 3 different types of mycotic infections and describe these briefly?
- Superficial: surface epidermis and outer layers of hair and claws
- Intermediate: infections of dermis and subcutaneous tissue
- Deep: involve body organs
Describe the pathogenesis of dermatophytes
- Use keratin in skin, nails, claws and hair to grow
- Are confined to superficial layers of the skin
- Only invade keratin of growing (anagen) hairs hence circular spread from initial infection site
What are the most common species that cause dermatophytosis?
- Cats and dogs: T. metagrophytes, Microsporum canis
- Cattle: T. verrucosum, less commonly also T. mentagrophytes
- Horses: T. equinum
Which individuals are most at risk of dermatophytosis?
- Cats more affected than dogs
- No breed or sex predisposition
- Especially common in young animals
What are the consequences of dermatophytosis?
- Not debilitating, but effect on animal and hide value
- Horses cannot race if have active infection
- In cats, M. canis may cause no clinical signs (natural host)
- T. mentagrophytes can cause serious and severe infection in dogs and cats as are not the natural hosts (mice/voles natural hosts)
Describe the clinical signs of dermatophytosis
- Lesions variable
- Often circular, patchy alopecia
- Variable erythema and variable pruritus
- Scale, crusts
- can be local, patchy or generalised (Trichophyton more generalised in dogs)
- Nails tend to be affected (loss, regrow often deformed, onychomycosis)
- In horses often tack contact areas
- Mass lesions (kerions) seen as lumps and bumps (rare)
Outline dermatophytosis in rabbits
- T. metagrophytes and M canis most common (zoonosis)
- Young animals most susceptible
- Lesions often confined to pinnae and feet
What skin conditions are guinea pigs prone to?
- Dermatophytosis
- Mange
- Trichofolliculoma
What are the 3 most common yeast/yeast like cutaneous infectious agents?
- Candida
- Malassezia
- Trichosporon
What group of individuals are most susceptible to Candida infections?
Immunocompromised hosts
What species of Malassezia is most commonly isolated from the skin of mammals and birds?
M. pachydermatitis
List the breeds that have higher skin levels of M. pachydermatitis
- Bassett hounds
- Daschunds
- Cocker spaniels
- WHWT
What conditions favour infection with M. pachydermatitis?
- Concurrent infection with Staphylococcus pseudintermedius
- Hot humid weather
Describe Malassezia dermatitis in dogs
- Seborrhoeic dermatitis: inflamed skin wih yeasty smell, increase production and change in nature of sebum
- Usually generalised
Describe the 2 types of Malassezia dermatitis
- Scaly: dry seborrhoea, dandruff, seborrhoea sicca
- Greasy: more common, seborrhoea oleosa
How are deep mycoses acquired?
- Direct inoculation traumatic implantation)
- Ingestion
- Inhalation or spores
What are the 2 subgroups of deep mycoses?
- Subcutaneous
- Systemic
Outline deep mycoses in cats
- Most common is Cryptococcus neoformans
- Cats with FIVE increased risk, more severe dsiease
Identify reservoirs for dermatophytosis
- Infected animals/contaminated environment
- Can survive in environment for many months
- Fomite spread
- Catteries/stables.yards carry high outbreak risk
Describe the 2 groups of carriers of dermatophytosis
1: Culture positive (dogs or) cats with subtle active infections
2: Culture positive (dogs or) cats with no active infection = carriers
Outline the control of dermatophytosis
- Self limiting if healthy, effective immune response
- Vaccine available
Describe the equine epidemiology of dermatophytosis
- Common, esp. in young horses
- Subsequent exposure leads to less severe signs
- Common sits of infection around tack
Explain the pathogenesis of Malassezia dermatitis
- Primary condition allows yeast overgrowth
- Yeast lipases alter surface lipid, causing smell
- Epidermal turnover rises causing scale
- Type I hypersensitivity to yeast develops
- Vicious cycle, need to kill yeast to stop
Describe ringworm pathology
- Incubation period ~1 week
- Spores of fungus invade anagen hairs
- Germinate and produce hyphae, invasion by digestion of keratin
- New arthrospores produced from hyphae
- Hair breaks off due to weakening leading to partial alopecia
- Inflammatory reaction lead to folliculitis or furunculosis
- Often red +/- pruritus,
- Can develop into deeper tissues
Describe the common clinical signs of Malassezia dermatitis
- Variable, usually generalised
- Mostly affects hot/moist areas e.g. ears, pinnae, under tail, skin folds
- Erythema, scale, greasy coat, otitis externa (may be only sign), variable pruritus, variable alopecia
- Yeasty smell, especially with otitis
- Eith chronic conditions will have lichenification and hyperpigmentation
Describe the appearance of Cryptococcus neoformans infections
Ulcerated skin lesions
Outline the methods used for the diagnosis of dermatophytosis
- Trichogram: suspend in 10% KOH, look for hyphae and arthrospores
- Wood’s lamp examination: some M canis strains fluoresce apple green, may get false positives and false negatives
- Fungal culture, McKenzie toothbrush culture: pluck fluorescing hairs from edge of lesion of skin scrape edge of lesion. Comb coat with sterile toothbrush esp. if o obvious lesions (good for screening in contacts/sources)
- Skin biopsies (histo +/- culture)
Describe the method for fungla culture
- Sabouraud’s method
- Takes 1-3 weeks
- Used to identify type of dermatophyte
- Grow in Sabouraud’s dextrose based media
- Useful for rapid growth of dermatophytes, inhibitis saprophytic fungi
- pH red with increased pH of alkaline products from pathogenic fungi
- Does not enhance sporulation of dermatophytes needed for speciation
What is contained in Sabouraud’s media?
Contains phenol red pH indicator, cyclohexamide to inhibit growth of other fungi and gentamycin and chlorotetracycline to inhibit bacterial growth
What media can be used for sporulation of dermatophytes to facilitate speciation?
- RSB
- Contains bromothymol blue indicator and chloramphenicol instead of gentamycin
What is the function of dermatophyte arthrospores?
Required for transmission
What are conidia?
Asexual, non-motile spores of a fungus and normally stained with lactophenol cotton blue
Explain how dermatophytes can be differentiated from one another
- Trichophyton: macroconidia up to 50um long, thin smooth walls, microconidia approx 4um
- Epidermophyton: macroconidia up to 15um, thin smooth walls, microconidia absent
- Microsporum: macroconidia up to 125um long with thick rough walls, microconidia approx 4-7um long
How is Malassezia dermatitis diagnosed?
- dermatological signs
- Acetate tape test (ancilliary diagnostic aids)
- Impression smear
- Fungal culture may be needed
Describe the diagnoses of deep mycoses
- In a chronic non-healing lump, consider Cryptococcus as a potential diagnosis
- Care - may be mycobacteria or fungal, esp. if ulcerated and chronic
- Biopsy required for diagnosis
Outline the management of dermatophytosis
- Vaccination
- Licensed antifungal agents
- Malaseb shampoo
- Spontaneous resoution in cattle and horses, rarely treated
What drugs are commonly used in the treatment of dermatophytosis in rabbits?
- Topical miconazole or clotrimazole
- Oral itraconazole or griseofulvin usually effective
Which antifungal drugs are licensed for the treatment of dermatophytosis?
- Systemic: azoles (itraconazole)
- Topical: azoles, enilconazole for cattle, horse, dog. Miconazole for cats
- Lime sulphur dip
- NB: griseofulvin no longer licensed for horses
Explain the use of malaseb shampoo in the treatment of dermatophytosis
Contains miconazole and chlorhexidine
Describe the treatment of malassezia dermatitis
- Treat primary cause
- Reduce organism numbers, topical treatment very effective
- Itraconazole if topical fails
- May need regular treatment, commonly with malaseb, chlorhexidine, mirobex, mycozole, seleen
Discuss the issues of dermatophytosis treatments
- Topical therapy does not work as sole treatment
- Little use for local therapy as spores elsewhere
- Clipping coat may benefit long haired breeds
- Environmental decontamination required: difficult, includes carpets, may need to repaint rooms
Discuss the advantages and disadvantages of coat clipping for the management of dermatophytosis?
- Physical removal of spores
- May also spread spores
- May damage skin allowing disease to establish itself more
Identify the important zoonotic fungal skin infections
- Ringworm
- Cryptococcus neoformans
List the vesicular diseases of large animals and identify those that are notifiable
- Notifiable: FMDV, vesicular stomatitis, swine vesicular disease, Bluetongue, Rinderpest
- Not notifiable: Malignant catarrhal fever, mucosal disease, infectious bovine rhinotracheitis, bovine herpes mammilitis
Describe the general clinical signs of vesicular disease
- Vesicles and erosions/ulcers on muzzle, oral mucosa, tongue, udder, teats, coronary band (can affect horn and hoof growth)
- May shed horns and hooves
- Non-haired areas more affected
- Often indistinguishable from one another
What samples can be used for virus isolation of a vesicular disease?
- Vesicular fluid
- Vesicular tissue
- Pharyngeal fluid
- Whole blood
Which samples can be used for RT-PCR of a vesicular disease?
- Vesicular fluid
- Vesicular tissue
- Pharyngeal fluid
- Whole blood
Which samples can be used for ELISA of a vesicular disease?
- Serum
- Milk
Which samples can be used for EM +/- histopathology if suspicious of a vesicular disease?
- Vesicular tissue
- PM tissue
How is FMDV spread?
- Vesicular fluid, saliva, milk, faces
- Contaminated fomites
- Airborne
Briefly describe vesicular stomatitis
- Never in UK
- Cattle, pigs, horses
- Motality moderate to low
- Spread by biting insects
- In people causes flu like symptoms, occasionally mucocutaneous vesicles and erosions
Briefly describe swine vesicular disease
- Pigs
- Eradicated from UK in 1982, endemic in Italy
- Mortality low, some loss of production
- Spread by direct contact, fomites, infected meat products
- Slower spread thn FMDV
Compare the disease caused by Bluetongue between species
- Affects sheep, cattle, deer, goats, camelids
- Sheep most severely affected, cattle are main mammalian reservoir and often clinically unaffected
Describe the transmission and control of Bluetongue
- Spread by Culicoides midges in late summer/autumn
- UK free after vaccination programme
- Still see in imported animals
Describe the clinical signs of Bluetongue in sheep
- Oral ulcers
- Discharge of mucus and drooling from mouth and nose
- Swelling of mouth, head and neck, and coronary band
- Occasionally purpura, fever, lameness, breathing problems
Which species are affected by Rinderpest?
Cattle, sheep, goats, camels, wild ruminants, pigs
Describe the general control of notifiable viral diseases
- Usually no treatment
- slaughter and disposal of infected and in contacts
- Quarantine/protection zone, movement restrictions, disinfection
- +/- vaccination
- Eradication programmes, surveillance programmes
- Reporting of confirmed/suspected cases
What virus causes malignant catarrhal fever (MCF)?
Herpesvirus
What species are affected by MCF?
Cattle, deer, sheep are an asymptomatic reservoir
What are the cutaneous signs of MCF?
- Crusting of muzzle
- +/- exudative dermatitis of udder/teats, inner thighs
What are the systemic signs of MCF?
- Fever
- Corneal opacity
- Mucopurulent oculonasal discharge
What virus causes Mucosal Disease (MD)?
Bovine viral diarrhoea virus (BVDV) - Pestivirus
What species are affected by Mucosal Disease?
Cattle
Describe the cutaneous signs of Mucosal Disease
- Salivation
- Ulcers on mouth/muzzle
Describe the systemic signs of Mucosal Disease
- Fever, anorexia
- Purulent discharge from eyes/nostrils
- Diarrhoea
- Thrombocytopaenia, haemorrhagic disease
What agent causes Infectious Bovine Rhinotracheitis (IBR)?
Bovine Herpesvirus-1
What species are affected by IBR?
Cattle
What are the cutaneous signs of IBR?
Ulcers on muzzle
Describe the systemic signs of IBR
- Fever
- Rhinitis, conjunctivitis, fever
- +/- dyspnoea, cough
- Venereal transmission
- Abortion
What agent causes bovine herpes mamillitis?
Bovine herpesvirus-1
What are the clinical signs of bovine herpes mammillitis?
- Ulcerative lesions of teats and udder
- Decreased milk production
- Mastitis
Describe the spread of bovine herpes mammillitis
- Spread by insects and carrier cattle
- Rapid spread, high morbidity
- Mainly autumn and winter
What are the consequences of bovine herpes mammillitis?
- Severe economic losses
- Difficult to control
- Zoonotic
- Often persistently infected herds
How many types of bovine papillomavirus are there and which are important in the skin?
- 6 types
- I, II, III, V and VI important in skin
Describe the significance of cutaneous papilloma virus infection in cattle
- Highly prevalent in UK
- 50% of cattle have lesions
- Rarely cause problems, unless on teats or genitals
- May become secondarily infected
- Unsightly, may be problem on show animals
Describe the appearance of cutaneous bovine papilloma virus lesions
- Can appear very variably
- Large cauliflower like masses on head, neck and shoulders
- Flat wide-based warts
- Pedunculated masses
- Aka Angleberries, cutaneous warts
How is cutaneous bovine papilloma virus spread?
- Warts contain large amounts of infectious material
- Trauma on fence posts, halters, contaminated tagging equipment leads to transmission
Describe the treatment for cutaneous bovine papilloma virus
- Treatment not usually required, spontaneous regression
- Surgical removal if pedunculated
- Disinfect stalls, fence posts and other environmental reservoirs
- Autogenous vaccine can be used, but ineffective against existing warts
What is the significance of bovine papilloma virus for other large mammals?
- BPV I and II can induce sarcomas and fibrosarcomas in other mammals
- Equine sarcoids for example
- Transmission unclear, may be flies or contaminated tack
- Causes warts, or aural plaques
- IN young horses is self limiting, if over 1yo will persist
- Is only known example of natural cross-species infection by a papillomavirus, others are very species specific
Describe the clinical signs of classical swine fever (identical to African Swine fever)
- Fever, constipation/bloating
- Conjunctivitis
- Blotchy discolouration of skin
- Abortion,still birth, weak litters
- Hindlimb weakness
- Nervous signs
Describe the spread of classical swine fever
- Recovered pigs excrete virus for long periods, can be active for months
- Spread by eating infected pork or pork products
- Movement and fomites
What are the differential diagnoses for classical swine fever?
- Post-weaning multisystemic wasting disease
- Porcine dermatitis nephropathy syndrome (blotchy skin)
- Circovirus
- Ubiquitous
Describe the clinical signs of congenital infection, and in ewes with border disease
- Hairy shakers/fuzzy lamb disease
- Small, weak lambs
- Abnormally hairy birth coat
- Tremor of skeletal muscles
- Leads to death
- In ewes causes abortion/still birth
How is Border disease spread?
- If infected in first half of gestation = persistently infected sheep
- These act as source of infection for pregnant ewes
Outline the control of Border disease
- Prevention of exposure of pregnant ewes to persistently infected sheep
- No vaccine
Describe the dermatological signs of Pox viruses
- Macules
- Papules
- Vesicles
- Pustules
- Crusts
Give examples of pox viruses and briefly describe each
- Cowpox: rarely in cattle, reservoir in rodents, more frequently seen in cats
- Horsepox: rare in Europe
- Swinepox: transmitted by sucking lice, mild self-limiting disease
Briefly describe sheep and goat pox (significance and clinical signs)
- Notifiable, not present in UK
- Papules and crusts on eyes, nose, mouth, udder and teats, non-woolled skin
What agent causes lumpy skin disease?
Capropoxvirus
Describe the distribution of lumpy skin disease globally
Moved from Africa/Asia to Middle East to Eastern Europe, risk of introduction to UK, isolated case in Ireland. Notifiable
Describe the transmission of lumpy skin disease
- Transmission by biting insects/ticks
- More common in summer
