Equine Medicine Board ReviewEquine Medicine Board Review

Prepared by:Beatrice Sponseller, Dr. med. vet., DABVP

Respiratory DiseaseRespiratory DiseaseI. Disorders of the lower respiratory tract

1. Recurrent Airway Obstruction (RAO, COPD, heaves)

2. Pneumonia / pleuropneumonia

3. Exercise-induced pulmonary hemorrhage (EIPH)

1. Recurrent airway obstructionType I / III hypersensitivity reaction to

environmental allergens (dust, mold, pollen, pasture)

Bronchiolitis, bronchoconstrictionClinical signs: expiratory effort (heave line),

chronic cough, mucopurulent nasal discharge, exercise intolerance, weight loss

Dx: - clinical signs (wheezes; afebrile) - BAL (neutrophils & mucus)

Tx: - reduce/eliminate exposure to allergen- corticosteroids (dexamethasone, prednisolone) - bronchodilators

2-agonists (clenbuterol, albuterol)

- systemic and/or inhalation therapy

2. Pneumonia/PleuropneumoniaBacterial, viralFoals: Strep. zooepidemicus, Actinobacillus spp.,

R. equi (< 6 months).[Pasteurella spp., Bordetella bronchiseptica, enterics]. Anaerobes rare.

Adults: Strep. zooepidemicus, Actinobacillus spp., gram neg. enterics. Anaerobes common.

Dx: - thoracic auscultation, U/S, radiographs- TTW, thoracocentesis

Tx: - antimicrobial & antiinfl. medication- nasal O2 insufflation- pleural drain, lavage

3. Exercise-induced pulm. hemorrhageCause unknown; stress failure of capillaries

due to pulmonary hypertension?Associated with strenuous athletic events (race

horses; 44-75% prevalence in TB)Caudodorsal lung field affectedEvidence of frank blood in <10%Dx: - endoscopy, TTWTx: - furosemide, bronchodilators

II. Disorders of the upper respiratory tract

1. Left laryngeal hemiplegia (roarer)

2. Dorsal displacement of soft palate (DDSP)

3. Sinusitis

4. Ethmoid hematoma

5. Guttural pouch disorders

6. Strangles

1. Left laryngeal hemiplegiaDistal axonopathy of recurrent laryngeal nerve

neurogenic atrophy of intrinsic laryngeal muscles Loss of abduction of arytenoid cartilage (CAD)Inspiratory noise during exercise +/- exercise

intolerance (fatigue)More common in large horsesDx: - laryngoscopy (grades 1 to 4)Tx: - Laryngoplasty +/- ventriculocordectomy

2. Intermittent DDSPInspiratory + expiratory gurgling noise Exercise intolerance, temporary asphyxiaCause: ?? - laryngopalatal instability due to airway inflammation,hypoplastic or flaccid

epiglottisDx: - laryngoscopy at rest (nasal occlusion)

and during treadmill exerciseTx: - tongue tie, figure-8 nose band

- staphylectomy, strap muscle resection (sternothyrohyoid myectomy)

3. SinusitisPaired dorsal, middle, ventral conchal, frontal, maxillary, sphenopalatine sinusesAll sinuses drain into max. sinus nasomax.

opening middle nasal meatusCause: - primary sinusitis (-hem. strep., fungal)

- dental disease (P4, M1 most common)- paranasal sinus cyst (usually <2 years)- neoplasia- ethmoid hematoma

Dx: - radiographs, sinuscopy, C&S, biopsyTx: - medical / surgical; lavage, …..

4. Ethmoid hematomaProgressive, locally destructive angiomatous massOriginating from ethmoid labyrinth (or sinus) Cause unknown; more common > 8 yearsFacial distortion, respiratory noise, brownish /

hemorrhagic nasal dischargeDx: - endoscopyTx: - 10% formalin (10cc) injections q 10 days

- laser resection, cryosurgery -Recurrence common

5. Guttural pouch disordersAuditory tube diverticula; med.>lat. compartmentAssoc. structures: CNN VII & IX-XII, int. & ext.

carotid artery, max. vein, symp. trunk, stylohyoid A. Guttural pouch tympany

- non-painful air distention; young foals - may cause stridor/resp. distress, dysphagia, aspiration pneumonia, nasal discharge - functional defect of pharyngeal opening ? - Dx: endoscopy, radiographs, -

Tx: - surgical

B. Guttural pouch empyema - exudate/pus filled GP- chondroids (inspissated pus) in chronic cases- associated with upper respiratory tract infection (Strep. equi / Strep zooepidemicus)- white, nonodorous nasal discharge, dysphagia,

lymphadenopathy, painful distention in parotid area- Dx: radiographs, endoscopy- Tx: - medical (lavage, C&S, antimicrobial tx) - surgical

C. Guttural pouch mycosis- fungal plaques on GP mucosa assoc.

with internal (70%) or ext. carotid artery; most commonly Apsergillus- bouts of severe (bilat.) epistaxis +/- dysphagia - mortality 60% (fatal hemorrhage)- Dx: endoscopy- Tx: surgical balloon catheterization of affected

artery

6. StranglesStreptococcus equi subsp. equi infectionClinical signs: fever (103-106oF), depression,

anorexia, serous mucopur. nasal discharge, abscessation of mandibular/retropharyngeal Lnn

Complications: acute URT obstruction / resp. distress, (aspiration) pneumonia, GP empyema, ‘bastard strangles’, purpura hemorrhagica, Strep. myopathy

Highly contagious; morbidity 30-100%Young horses (<5 years) more severely affected

Dx: - culture of organism from nasal swab or abscess

- radiographs (GP/retropharyngeal area)Tx: - hot packing/surgical drainage/lavage of abscesses

- antimicrobial (penicillin) therapy in severely affected animals (foals!)

- NSAIDs (antipyretic/antiinfl.)

Stringhalt Spastic intermittent hyperflexion of hindlimb(s)

Cause: Peripheral nerve trauma or ingestion of toxic weed (Hypochoeris radicata)

Tx: tenectomy of lat. digital extensor muscle

Shivers Idiopathic neuromusc. disease (draft horses: PSSM?)

Trembling of hind limb and tail (esp. backing)

Hyperkalemic periodic paralysis (HYPP) Autosomal codominant gen. dz (point mutation in

voltage gated Na channel of skeletal muscle)

Na channels fail to inactivate K+ leaves cells hyperexcitability, muscle fasciculations/spasms, recumbency, laryng./pharyng. paralysis, collapse, death “Impressive” descendents (QH, Paints, Appal.)

Dx: - DNA testing (mane/tail hair, blood)

Tx: Dextrose (insulin), sodium bicarb. (K+) Calcium gluconate

Prevention of attacks:

- low K+ diet (avoid alfalfa, molasses, timothy; feed

oat/grass hay or pasture)

- regular exercise or access to paddock

- K+ excretion (acetazolamide)

Nutritional myopathy ‘White muscle disease’, Vit.E/Se deficiency

Foals from birth to 11 months of age: muscle weakness, dysphagia, hard/painful muscles (acute and subacute forms)

Dx: CK + AST, myoglobinuria, low blood Se and/or glutathionperoxidase levels, response to Vit. E/Se.

Prevention: Se supplementation of pregnant mares and/or foals from birth to 6 months of age

Exertional rhabdomyolyis Stiff gait, muscle cramping, exercise intolerance,

recumbency, death

CK (acute myonecrosis), AST, myoglobinuriaA. Polysaccharide storage myopathy (PSSM)

QH-related breeds, warmbloods & draft horses

Accumulation of glycogen + abnormal PS due to increased insulin sensitivity of skeletal muscle

Dx: - CK>1000U/l 4h post exercise (15 min. trot)

- gluteal or semimembranosus muscle biopsy

Tx: Acepromazine, NSAIDs, IV fluids,

DMSO, Methocarbamol, Vit. E/Se, sedatives

Prevention :

- dietary management (carbohydrates: no grain,

sweet feed, alfalfa; instead feed grass/oat hay + fat

supplement [1-4 cups vegetable oil/d, or rice bran])

- regular exercise or access to paddock

- selective breeding (autosomal recessive trait)

Clostridial myositis Within 2 days of intramuscular nonantibiotic

injection (Banamine!) or injury (chest wound)

C. septicum, chauvoei, perfringens, sordelli, novii

Painful, hot, soft swelling cool, firm, +/- crepitus

Dx: needle aspirate, anaerobic culture

Tx: - antibiotics (IV penicillin, oral metronidazole)

- surgical incision and drainage

- NSAIDs

-

Neurologic DiseaseNeurologic DiseaseBotulism

Flaccid paralysis due to inhibition of ACh release from cholinergic neurons

8 distinct Clostr. botulinum strains; horses affected by types (A), B & C

Clin. signs: gen. muscle weakness recumbency, tremors, dysphagia, hypotonia of tail, ptosis, mydriasis, death

3 routes of infection

1. Forage poisoning (ingestion of preformed toxin)

- decaying vegetable matter (type B) or animal

carcasses (type C)

2. Toxicoinfectious botulism (shaker foal syndrome)

- ingestion of spores proliferation in GI

- foals from 2-8 weeks of age affected

3. Wound botulism (wound infection, anaerobic cond.)

- injection site abscess, trauma, castration, omphalo-

phlebitis

Dx: - mouse bioassay

- ELISA, PCR to detect toxin

- C. botulinum spores in feedstuff or feces

Tx: - polyvalent antitoxin

- supportive care (mechanical ventilation)

- +/- antibiotics (avoid aminoglycosides, procaine

pen., tetracyclines; metronidazole is ineffective)

Prevention: C. botulinum type B toxoid

Tetanus Spastic paralysis due to inhibition of neurotransmitter

release centrally from inhibitory interneurons

Clostr. tetani toxins: Tetanospasmin neurotoxin Tetanolysin facilitates spread of infection via

tissue necrosis Non-spasmogenic toxin symp. hypertension

Clin. signs: gen. increased muscle tone, trismus, erect ears, stiff gait, elevated tail, sawhorse stance, prolapsed nictitans, convulsions, death (resp. arrest)

Tx: - antitoxin (IV, intrathecally)

- antimicrobials (Pen. G, metronidazole,

tetracycline)

- muscle relaxation (aceprom., diazepam, pentobarb.)

- wound debridement, lavage (H2O2)

- quiet environment, sedatives

- supportive care

Prevention: Tetanus toxoid

Equine protozoal myeloencephalitis (EPM) Focal or multifocal CNS disease caused by Sarcocystis

neurona

Obligate two-host-species life cycle

Definitive host: opossum (oocysts with sporocysts in feces)

Intermediate hosts: cat, armadillo, skunk, raccoon,

(sea otter), bird

Aberrant host: horse (tachyzoites & schizonts in CNS)

Clinical signs of EPM:

Spinal cord: asymmetric ataxia (rear>front), muscle atrophy (gluteal), weakness

CN (10%): facial paralysis/vestibular signs, dysphagia, blindness

Cerebrum: Seizures, depression, central blindness

Dx: - CSF analysis (western blot, PCR, cytology)

- Serology (only neg. result diagnostic)

- Response to treatment (sulfonamide /pyrimethamine,

ponazuril)

Equine herpes myelitis neurologic form of EHV-1 infection

Vasculitis (esp. small arterioles of white matter tracts)

Symmetrical ataxia (esp. rear limbs), cauda equina syndrome (weak tail, bladder paralysis, penile prolapse)

CN deficits rare

Dx: - CSF analysis (xanthochromia, high protein,

normal cell count)

- serology ( 4x titer increase)

- nasopharyngeal swab (virus isolation, PCR)

Tx: - NSAIDs, corticosteroids, DMSO

- supportive care (bladder catheterization, etc.) - antiviral medication (acyclovir)

Prevention: EHV-1 vaccine does not prevent neurologic form (but may reduce exposure to virus).

Vaccination contraindicated in outbreaks.

Prognosis: good in most cases (if not recumbent).

Horses may recover within 7-10 days, or

gradually improve over months.

Cervical stenotic myelopathy (Wobbler syndrome) Developmental orthopedic disease

Multifactorial etiology (diet - low Cu, high Zn, high CHO; genetics – rapid growth)

TB predisposed; male>female; onset ½ - 3 years of age

Dynamic compression: vertebral instability (C3/4, C4/5)

Static compression: spinal canal narrowing (C5/6, C6/7)

Clinical signs: symmetric ataxia (rear>front), front limb involvement marked with C6/7 compression

DD: Herpes myelitis, equine degen. myeloencephalo-pathy (EDM), EPM, atlanto-occipital malformation

Dx: cervical radiographs (sagittal ratio), myelography (obliteration of 50% of ventral & dorsal contrast column), CSF analysis

Tx: - stabilization with NSAIDs, corticosteroids, DMSO

- ‘paced diet’ (<1 year old): restricted (65% NRC) energy/protein, increased vit. A, E,

Se, balanced minerals

- cervical vertebral interbody fusion

West Nile virus encephalomyelitis Arbovirus genus flavivirus; reservoir: birds (viremia)

Transmitted by mosquitoes (prim. Culex)

Short lived, low level viremia in horses

Clinical signs: ataxia (asymmetric), hypermetria, muscle tremors (triceps, facial), lip twitching, recumbency, seizures, hypersensitivity to touch/sound, +/- fever

Dx: - IgM capture ELISA (low in vaccinated horses)

- plaque reduction virus neutralization test

- post-mortem: virus isolation/immunohistochem.

DD: -virus infection (EEV, WEV, VEV), EHV-1,

EPM, rabies, leukoencephalomalacia (moldy corn pois.)

Tx: - NSAID (flunixin-meglumine)

- corticosteroids (low dose, few days)

- DMSO, mannitol

- hyperimmunized plasma (first 72 hrs)

- supportive care

Prevention: - vaccination

- eliminate mosquito breeding sites

Rabies Sylvatic reservoirs: skunks, raccoons, foxes, bats

Incubation period: 2 weeks to several months

3 forms: Brainstem (dumb), cortical (furious), spinal cord (paralytic / ataxic)

Clinical signs: ataxia, paresis, lameness, colic, fever, dysphagia, hyperesthesia, death (resp. or cardiac arrest)

Dx: FA test (tactile hair), Negri bodies in hippo-campus and Purkinje cells of cerebellum

Exposed horse: euthanize unless vaccinated (booster & observe for 3 months)

Endocrine DiseasesEndocrine DiseasesEquine Cushings Pituitary pars intermedia dysfunction due to loss of

dopaminergic inhibitory control Hypertrophy, hyperplasia, adenoma (rare) production/secretion of POMC-derived peptides

(-END, -MSH, ACTH) by melanocytes in pars intermedia

loss of circadian pattern of steroid secretion (<30% difference AM vs PM)

Age: 7-42 years (85% > 15 y), high incidence in ponies

Clinical signs:

- hirsutism (long, thick, often curly hair, won’t shed)

- PU/PD (ADH; GFR; hyperglycemia…)

- intercurrent disease problems (dental, GI parasites)

Dx: - cortisol level in PM <30% lower than in AM

- dexamethasone suppression test

Tx: - pergolide (0.5 – 2 mg PO SID)

- cyproheptadine (0.25 mg/kg PO SID)

Sudden death in parturient mare hemorrhage from ovarian artery Renal tubular necrosis aminoglycosides

Renal failure acute tubular necrosisLate abortion Herpes

Bacterial pneumonia Strep zooNeural disease EPM

Colic in minis small colon impaction Site of impaction pelvic flexure

Intussusception Ileocecal valveDegenerative heart valve aortic valve

The “Most Commons” in the Horse

The “Most Commons” in the Horse

Heart disease myocarditisFractured bone in fatigue first phalanx

Congenital heart anomaly ventral septal defect Acquired hear anomaly mitral insufficiency

Pathologic arrhythmia atrial fibrillation Physiologic arrhythmia second degree AV block

Diarrhea in foals Rotavirus Pleural effusion pleuropneumonia

Icterus anorexia, hemolysisParaphimosis trauma

DermatologyDermatologyI. Crusting and Scaling Diseases

1. Dermatophilosis (rain rot, rain scald)

2. Dermatophytosis (ringworm)

3. Pemphigus foliaceus

4. Sarcoidosis (gen. granulomatous dz)

5. Pastern dermatitis (scratches, grease heel)

1. DermatophilosisDermatophilus congolensis Moisture + mechanical irritation invasion of

Stratum corneum by zoospores proliferation of mycelium

Dx: - direct smear/gram stain: railroad tracks (grampos. filamentous bact.)

- cultureTx: - antiseborrheic/antiseptic shampoo

- Povidone/iodine, chlorhexidine - Penicillin

2. DermatophytosisTrichophyton equinum, T. verrucosum,

T. mentagrophytesMicrosporum gypseum, M. equinum, M. canisHighly contagious; highly resistant spores

invade areas of skin abrasions (girth etc.)Initially circular lesions (5-20mm) alopecia

(14 days) scabGeneralized in young, less resistant horsesWinter (crowding); wet/warm weather

Dx: - KOH prep: hyphae and spores - culture of hair plucking (fresh lesion!) on Sabouraud’s agar red color- Wood lamp/UV fluorescence: M. equinum + some M. canis only

Tx: - spontaneous resolution (6-12 weeks)- sunshine

- fungicidal washes (miconazole / chlorhexidine)- topical: 10% povidone-iodine, 2.5% lime sulfur in H2O, …

- systemic: griseofulvin efficacy???

3. Pemphigus foliaceusAutoimmune (type II) exfoliative dermatitis Appaloosa breed predisposedVesicles/pustules (face/limbs) erosions

epidermal collarettes scales, crusts, alopecia (generalized)

Fever, lethargy, weight loss, ventral/limb edemaDx: - biopsy: acantholysis, nondeg. neutrophils

- direct IFA: variableTx: - corticosteroids

- gold injections

4. Pastern dermatitisEtiology: - Dermatophilosis

- Dermatophytosis- Staphylococcus sp.

- Chorioptic mites- Photoactivated vasculitis, …

Scales, crusts, alopecia (“scratches”) exudative dermatitis (“grease heel”) chronic granulation tissue (“grapes”)

Tx: - topical antiseptic washes- antifungal/antibacterial/antiinfl. lotions- keep dry

Also go overAlso go over

Neonatal IsoerythrolysisLethal White Foal (myenteric aganglionosis)Ruptured Bladder

II. Parasitic Skin Diseases

1. Pediculosis (lice)

2. Mange (mites)

3. Habronemiasis

4. Onchocerciasis

1. PediculosisDamalinia equi (biting louse; head>thorax)Haematopinus asini (sucking louse) Life cycle 20-40 daysMore common in winterPruritic if severe infestationDx: - macroscopic/microscopicTx: - bath/spraying/pour-on anti-

ectoparasitics (pyrethrins)- repeat in 2 weeks- oral ivermectin (limited effect)

2. MangeChorioptes equi

- non-burrowing mite, feeds on skin debris- leg and tail mange - most common mite infestation in horses- in winter / horses with feathered fetlocks

Psoroptes equi - sucking mite, feeds on blood and tissue fluid- body mange (ears, mane, body, tail head)

Mange cont. Sarcoptes scabei var. equi

- digging mite, feeds on tissue fluid and cells- head/neck/ears entire body- intense pruritus, automutilation- notifiable disease; rare in horses

Dx of mange: - microscopic (skin scrapings)Tx of mange: - whole body baths with anti-

ectoparasitic drugs (tack etc.) - repeat in 2 weeks - oral ivermectin (limited)

3. Habronemiasis (summer sores)Habronema muscae, H. majus, Draschia

megastoma (stomach nematodes)Larvae can penetrate intact skinEye (conjunctival/lacrimal), legs, ventrum,

prepuce, urethral process, wounds Hypersensitivity reaction/genetic predispos.?Dx: - impression smears; ‘sulfur granules’Tx: - surgical curettage/removal

- topical/systemic ivermectin- intralesional/systemic steroids

                              

                  

4. OnchocerciasisOnchocerca cervicalis (microfilaria)Transmitted by Culicoides spp + biting fliesType I, III hypersensitivity dermatitisVentral midline, chest, withers, face, neckPruritus, patchy alopecia, thickened, scaly skinDx: - season, clinical signs, history

- biopsy: microfilaria (incidental?)- response to ivermectin (circular

exudative dermatitis)Tx: - oral ivermectin

III. Other Skin Diseases

1. Urticaria

2. Insect hypersensitivity

3. Sarcoid

4. Nodular necrobiosis

1. Urticaria (hives)Type I hypersensitivity IgE mediated mast cell

degranulation vascular permeability wheal formation

Etiology: Immunological : systemic/topical drugs

(Penicillin!), ingested (feed) or inhaled (dust, mold, pollen) antigens

Physical: stress, cold, heat, exercise inducedTx: - corticosteroids

- avoid causative antigen/allergen

2. Insect hypersensitivity‘Sweet itch’, ‘summer itch’, ‘Queensland itch’Type I hypersens. to culicoides (or simulium) salivaGenetic predisposition? (Welsh ponies, Icelandic

horses, Shires, Friesians)Seasonal, progressive Severe pruritus, main & tail, ventral midlineSkin thickening, severe hair loss, self mutilationPrevention: blankets, repellents, fans, stabling at dusk

and dawnTx: corticosteroids

3. Equine sarcoidFibroblastic tumor of viral etiology (bovine

papillomavirus, BPV1 and/or 2)BPV present in sarcoids and normal skin of

horses with sarcoids virus latency?Genetic predisposition, MHC-II linked (QH,

Appaloosa, Arabian)Location: head/ears, limbs, abdomen, sites of

trauma/healed woundsTypes: occult (flat), verrucous (warty),

fibroblastic, nodular, mixed

Types: - occult (flat) - verrucous (warty)

- fibroblastic - nodular

- mixed Tx: - Surgery

- Cryotherapy - Immunotherapy (BCG) - Brachytherapy (radiation) - Chemotherapy (cisplatin)

4. Nodular necrobiosis (collagenolytic granuloma)

Asymptomatic small nodules in skinCollagen necrosis and eosinophiliaEtiology: ??? (trauma, insect bites,

hypersensitivity)Tx: - none

- intralesional triamcinolone