Equine dermatology, diarrhoea, parasites Flashcards
What is the most common secondary infection of wounds and other skin damage in horses? Signs?
Streptococcal dermatitis: Strep equi var zooepidemicus: - opportunistic pathogen - folliculitis, furunculosis, cellulitis Strep equi var equi: - obligate pathogen - abscesses (bastard strangles) Strep equisimilis
Signs, diagnosis and treatment of streptococcal dermatitis?
Signs: - mild-moderate painful skin infections and abscesses Diagnosis: - clinical features and culture Treatment: - sensitive to penicillin - drain abscesses - topical antimicrobial washed in superficial infections
Staphylococcal dermatitis in horses: Most common species? Signs?
Treatment?
Staph aureus and intermedius Signs: - pain - localised exudative dermatitis - focal lesions also occur (abscesses or pyogranulomas) Treatment: - problematic! - clip hair and antiseptic washes with warm water - drain abscesses - systemic antibiotics based on C and S
What are the 5 clinical syndromes of Staphylococcal dermatitis in horses?
- Pyoderma: secondary to trauma, large painful exudative areas
- Saddle rash: associated with harness areas and saddle cloths
- Pastern folliculitis
- Wound infections
- Abscesses
What causes rain scald in horses? Clinical presentation and signs? Diagnosis?
Dermatophilus congolensis: gram positive, facultative anaerobe
Very common
Contagious
Signs/presentation:
- affects areas that are commonly or persistently soaked: back, head, neck
- initially small lesions, easier felt than seen (common presentation in summer)
- more severe disease in winter: moist matted hair, adherent crusts with purulent base
- pain usually mild
Diagnosis:
- easily recognised clinically
- direct smears: cytology
- culture
Treatment:
- remove to dry environment
- remove matted hair and crusts
- antimicrobial washes (dilute chlorhexidine)
- systemic antibiotics if severe
Ringworm in horses: Cause? Incubation period? Immunity? Signs? Diagnosis? Treatment?
= Dermatophytosis
Trichophyton equinum var equinum
Trichophyton verrucosum
Microsporum gyspeum
Microsporum equine
Highly contagious
Incubation period 2-3 weeks
Very common in young and immunocompromised
Some immunity with age - older horses can be re-infected but with smaller, quicker resolving lesions
Signs:
- small circular patches of hair sticking up
- accumulation of keratinised squames ("cigarette ash")
- weakening of hair -> bald patches
- poss secondary bacterial infections
- healing centrifugally from centre of lesion
Diagnosis:
- skin scrapes
- hair pluck
- culture (takes long time)
Treatment:
- isolate
- most are self limiting in 5-10 weeks
- topical natamycin, enilconazole, miconazole
- systemic treatment?
- environmental and tack disinfectionWhat causes grass warts in horses? Which horses? Signs? Diagnosis? Treatment?
= viral papilloma Host specific Papovavirus Affects mainly younger horses (6mo-4y) or immunocompromised Moderately contagious Multiple pink or grey lesions on muzzle, lips, face, limbs and genital areas No discomfort or pruritus Diagnosis: - straightforward - biopsy? virus isolation? Treatment: - spontaneous resolution in most cases - surgical excision? topical antivirals? - autogenous vaccination?
What causes pinnal acanthosis/aural plaques in horses? Signs? Diagnosis? Treatment?
Very common
Papillomavirus transmitted by black flies (Simulium spp)
Range from small raised depigmented areas to large clusters of white masses
Diagnose on signs (don’t biopsy)
Treatment:
- not necessary
- do not treat
Coital exanthema in horses: Cause? Transmission? Incubation period? Immunity? Signs? Diagnosis? Treatment?
Contagious, venereal disease caused by EHV-3
Transmission also by indirect contact and by inhalation of virus-laden droplets
Incubation period 5-7 days
Only significant in breeding animals
Solid immunity: most horses only infected once
Signs:
- Rapidly developing papule (1-5mm) on penis, vulva and perineum
- Lesions can be mildly pruritic but not painful
- Healing of lesions may leave permanently depigmented spots on skin
Diagnosis:
- Clinical signs
- Virus isolation difficult
Treatment:
- Stop breeding until >3 weeks after the lesions have healed
- Topical antimicrobials/antiseptics
- Local anaesthetic creams
Horse pox: Forms? Signs? Treatment?
Very rare
Buccal form and cutaneous form
Mild systemic signs: fever and depression
No treatment: spontaneous regression
Papular dermatosis in horses: Cause? Signs? Treatment?
Very rare
Unspecified Pox virus
Annular papular lesions - non pruritic or painful
Most cases resolve in 4-6 weeks: no need for specific treatment
Sarcoids: What are they? Associations? Types?
Most common skin tumour in horses Fibroblasts Potential association with bovine papillomavirus 1 and 2 Genetic predisposition Flies 6 Types: - Occult: flat - Verrucose: bumpy flat - Nodular - Fibroblastic: angry red nodular - Mixed: made up of multiple types - Malignant: nasty, lots
Diagnosis of sarcoids? Treatment?
Biopsy: - histologically distinctive - danger of exacerbation so must treat if positive diagnosis (ie don't take sample if wouldn't be prepared to treat) Treatment: - surgery/cryo/laser - immune therapy: BCG injections, vaccines - cytotoxics (topical and injections) - antimitotics (topical) - photodynamic therapy - radiation - homeopathy/natural medicine
Prognosis rules for sarcoids?
Rule 1: the more they have, the more they get
Rule 2: the fewer they have, the fewer they get
Rule 3: multiply over summer, grow over winter
Rule 4: a single sarcoid implies (genetic) susceptibility
Differentials for acute colitis?
Idiopathic - most common Salmonella Clostridium perfringens and dificile Drug induced - antibiotics, NSAIDs Larval cyathostomosis Carbohydrate overload
Rotavirus - acute enterocolitis in foals
Ehrlichia risticii - Potomac Horse Fever (acute colitis)
Acute necrotic colitis and dysentery (Colitis X)
When should a horse be put in isolation for possible infectious colitis?
Any 2 of the following:
- Acute diarrhoea
- Fever (temperature >38.5)
Low white blood cell count (<4x10^9 cells/L)
Salmonella enterocolitis: Which species? Features of the bacterium?
Salmonella enterica
6 subspecies, especially subs enterica
>2000 serovars, especially Typhimurium
Host specific forms cause more systemic disease
Gram -ve motile bacillus
Modified flagella and pilli used for plasmid exchange
Facultative anaerobe
Facultatively intracellular - the most pathogenic strains are best at this
Wide range of antibiotic resistance
Survives in damp soil for up to 9 months
Contagious
Water and feed contaminated with faecal material
Recovered animals may shed for weeks or months (source of infection is asymptomatic shedders or diseased horses)
Mostly seen in hospitalised patients
Virulence factors of Salmonella enterica?
3 types of adhesion molecules
Invasion genes - encode proteins that cause ruffles in enterocyte membrane and Salmonellae become interiorised
Salmonella virulence plasmids - allow intracellular growth, serum resistance and cellular invasion
3 exotoxins that result in diarrhoea - cAMP, Cytotoxin, Phospholipase A activity
What host factors predispose to Salmonella enterica infection (and acute colitis in general)?
Antibiotic treatment GA Transport Competition Hospitalisation Surgery Feed changes Anthelmintic treatment Immunosuppression ANY STRESS
Pathogenesis of Salmonella enterica?
Opportunistic
LPS (endotoxin) triggers massive neutrophil dominated inflammatory cascade
Facultatively intracellular in macrophages
Inflammation and tissue necrosis -> leakage of protein and fluid -> diarrhoea
Exotoxins exacerbate inflammation and necrosis and promote more diarrhoea:
- Cytotoxin: morphological damage and increases penetration of mucosa
- Enterotoxins: increases sodium and water secretion
Diarrhoea and endotoxaemia -> severe shock and cardio-circulatory collapse
Variable mortality (related to virulence) - if hydration can be maintained, diarrhoea and inflammatory response eliminates infection and the mucosa heals
When can a horse in isolation with Salmonella be taken out of isolation?
5 faecal cultures q12-24h all negative
Or when goes home
Differentials for acute colitis?
Clostridium per
Clostridium perfringens and dificile colitis: Features of bacterium??
Saprophytic and part of normal intestinal flora
Large gram +ve endospore forming bacilli
Obligate anaerobes and haemolytic in culture
C perfringens:
- non motile
- type A most common in horses: enterotoxin (cytotoxic), alpha toxin (lecithinase: phospholipase activity), B2-toxin (toxigenic strain)
C dificile
- motile
- Toxin A: pro-inflammatory (IL-1 and TNF) = toxic to macrophages
Requires host ‘stress’ or intestinal flora change (e.g. grain overload, rapid diet change)
High mortality rates
Spore forming
Resistant to heat, cold and many disinfectants
Predisposing stress factors for Clostridial colitis in horses?
Intercurrent infections Extreme temperature Water deprivation Overcrowding Sudden change in diet Transportation Antibiotic therapy GA
Diagnosis of Clostridium perfringens and dificile colitis in horses?
Culture not reliable as part of normal flora and not all isolates toxigenic
Identification of C perfringens enterotoxin by ELISA or B2 toxin by ELISA or PCR
Identification of C dificile toxin A by ELISA or PCR
Rotavirus: Features?
Reoviridae genus
Strains appear predominately host speciesspecific
Coat protein VP4 is the haemagglutinin that dictates species susceptibility
VP4 protein - target Ag of neutralising Ab response
Contagious
Water and feed contaminated with faecal material
Survive in environment up to 9mo
Resistant to bleach disinfectant - ethanol, phenols and formalin can inactivate the virus
Pathogenesis of Rotavirus?
Virus ingested and infects absorptive epithelium of the apices of the villi
Mostly SI involved (occasionally colon)
Damage and loss of cells in villi leads to villus atrophy, resulting in poor nutrient absorption and osmotic diarrhoea
Virulent strains cause more necrosis and haemorrhage
Humoral response by host neutralises virus
Incubation period 18-24h
Disease course usually 5-7d (self limiting)
Recovered foals shed for 2 weeks
Low mortality but can be high morbidity (highly infectious - oubreaks)
Predisposing factors for Rotavirus diarrhoea?
Age <2mo (naive immune status) Intercurrent infections Extreme temperatures Poor food and water sanitation Overcrowding Transportation High levels of infection on property in previous year Stressed adult horses may intermittently shed
Diagnosis of Rotavirus? Treatment?
Clinical signs and identification of virus in faeces Electronmicroscopy (gold standard) ELISA Rule out concurrent disease Treatment: - vaccination - supportive therapy
Rotavirus vaccine?
Mare in months 8, 9 and 10 of each pregnancy
Relies on good passive transfer and protects for approx 60 days
What types of skin diseases cause pruritus in horses?
Parasitic skin disease
Hypersensitivities (allergies)
Which lice affect horses? Where on the body do they affect? Morphology? When seen? Signs? Diagnosis? Treatment?
Haematopinus asini: - sucking louse (feeds on blood) - mane, tail, fetlock and pastern Werneckiela: - biting louse (feeds on epidermal debri) - dorsolateral trunk
Permanent - die within days if off host
1 month life time - lays 200-300 eggs
Hemimetabolous
Morphology: small, wingless insects (0.5-8mm), flattened, stout legs, claws
More common in winter
Asymptomatic (naturally well tolerated in healthy animals) -> restless, poor appetite, poor coat, irritation -> severe debilitation
Diagnosis: demonstration of adults or eggs on hair
Treatment: pyrethrins, pyrethroids, permethrin, fipronil
Which mite causes intense pruritus with stamping of feet in horses? Other signs? Which horse breeds affected? When more common?
Morphology? Life cycle?
Chorioptes equi Chewing mite Host adapted strain of C bovis Affects lower limbs, especially if feathered fetlocks Other signs: - papules - crusty lesions - hair loss Draft breeds More common in winter Morphology: - rounded head - thumb print - unjointed pedicels which end in cup-shaped sucker Life cycle: - 6 legged larva hatches from egg, feeds and moults to 8 legged protonymph, tritonymph and adult - 3 week life cycle
Sarcoptes scabiei: where on body do they affect in horses?
Burrowing mange mite
Head, neck, ears -> entire body
Difficult to see on skin scrapings
Psoroptes equi: Where on body of horses does it affect? Morphology?
Rare Host specific Forelock, main and tail -> trunk Ears: head shaking Morphology: - 3 jointed pedicel - trumpet shaped suckers
How are mites diagnosed and treated in horses?
Diagnosis: skin brushings
Treatment:
- systemic avermectins (not licensed, e.g. doramectin in dectomax)
- topical lime sulphur, lindane, coumaphos, diazinon, malathion
(dog/cat frontline sprays)
(head and shoulders..)
Treat at 2 week intervals
Trombicula: What is seen? Where on body of horses?
Larvae of free living adult mites
Papules with small orange or red larvae in centre
Face, distal limbs, ventral thorax and abdomen
Dermanyssus gallinae: Where affected on horses?
Poultry mite
Head and legs
Same treatment as other mites and remove birds
Demodex: When seen in horses? Where?
Rare - check for immunosuppression
D equi: body
D caballi: eyelids and muzzle
Treatment for ticks on horses?
Topical pyrethrin, pyrethroid, fipronil, ivermectin
Onchocerca cervicalis: Where does it live in horses? What does it cause? Treatment?
Adult lives in nuchal ligament Microfilarie migrate to skin -> hypersensitivity Worse in spring and summer Face, neck, ventral chest and abdomen Ocular lesions Ivermectin (+ pred?)
Habronemiasis: What do they cause in horses? Treatment?
Flies -> larvae in skin or wounds
Ulcerative nodules in spring and summer
Exuberant granulation tissue with yellow granules
Ivermectin and corticosteroids
Oxyuris equi: What does it cause? Features of adults and eggs? Diagnosis? Treatment? Life cycle? PPP?
= Pinworm 'Anal rust' Adults: translucent yellowish-white, pointed tails, 1-10cm' Eggs: 80um, mucoid plug Perianal pruritus Diagnosis: clinical signs and cellophane tape Anthelmintics - challenge as lack of efficacy Life cycle: - direct - females lay eggs on peri-anal skin - eggs fall to ground - develop to L3 in the egg - ingested - larvae develop in mucosal crypts in LI - adults in lumen of LI PPP 5 months
What hypersensitivities are seen in the horse?
- Insect hypersensitivity
- Food allergy
- Contact allergy
- Atopy
- Urticaria
What causes insect hypersensitivity? How does it present? Risks? Treatment?
Culicoides spp
Dorsal surface of horse: mane, back, tail
Seasonal
Risks: standing water, dawn and dusk, no wind
Treatment: avoid contact, reduce hypersensitivity
Food allergies: how common in horses? Signs? Diagnosis?
Rare Pruritus \+/- Diarrhoea \+/- Respiratory signs Diagnosis: diet elimination
Contact allergies: how common in horses? What allergens? Diagnosis? Treatment?
Rare
Plants, chemicals, tack etc
Diagnosis: provocative exposure
Treatment: avoid contact
What is Atopy in horses? Diagnosis? Treatment?
Skin or respiratory condition Sensitivity to multiple allergens Diagnosis: intradermal skin testing Treatment: - avoid allergens - hyposensitisation - corticosteroids - antihistamines
How does urticaria look on horses? Cause? Treatment?
Wheals, oedema and often pruritus
Cause difficult to determine
Rule out food and insect allergy
Treatment: corticosteroids, antihistamines
Define scale, crust, erosion and ulcer?
Scale: dry, grey
Crust: yellow/red/brown, wet/damp
Erosion: superficial
Ulceration: deeper
