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What are the major equine respiratory viruses?
EHV-1, EHV-4, EIV
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What are the 3 syndromes associated with EHV1/4?
equine rhinopneumonitis, equine herpesviral myeloencephalopathy, equine herpetic abortion
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What are the slight differences b/w EHV-1 and -4?
- EHV-1: URT infection, abortion, severely compromised foals (fatal), neurologic disease
- EHV-4: primarily associated with MILD URT disease (but can also cause all the stuff listed above)
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What horses usually get disease caused by EHV-1 and -4?
weanling-aged foals (2-6months old)
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What's usually the source of rhinopneumonitis in weanling foals?
mom- clinically silent reactivation of latent EHV at foaling; foals develop clinical signs when maternal antibody wanes
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What are clinical signs of rhinopneumonitis? (6)
[MILD] fever, serous nasal d/c, cough, inappetence, submandibular lymphadenopathy, +/- secondary bacterial infection
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EHV-4 rhinopneumonitis is usually limited to _____(2)_____.
URT epithelium, regional lymph nodes
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EHV-1 rhinopneumonitis commonly causes... (4)
URT infection in weanlings, death in neonates, abortion, myeloencephalopathy [last 3 are VERY rare with EHV-4 but can happen]
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Neuropathogenecity is associated with a(n) __________; the associated clinical syndrome is...
mutation in viral DNA polymerase gene; cauda equine syndrome/ ascending myelitis
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Is EHV-1 myeloencephalopathy infectious?
YES can be spread from affected horses to in-contact animals
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How is EHV-1 diagnosed? (4)
virus isolation (nasal swab, whole blood), PCR (nasal swab, whole blood, fetal tissue), fluorescent antibody (nasal swab, fetal tissue), serology (serum)
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How is rhinopneumonitis caused by EHV-1 and -4 treated? (2)
[supportive] NSAIDs, ventilation, +/- antiviral drugs
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What is the prognosis for recovery for EHV-1?
- respiratory disease: uncomplicated
- abortion: good prognosis for future fertility
- neurologic disease: fair to good if not recumbant, guarded is recumbant
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What is important to remember about vaccination for EHV-1?
THERS IS NO VACCINE THAT PROTECTS AGAINST EQUINE HERPETIC MYELOENCEPHALOPATHY
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Equine influenza viruses are ____________ that undergo __(2)__ frequently.
orthomyxoviruses; antigenic drift and shift
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What are the 2 subtypes of influenza virus that are pertinent in horses?
H3N8, H7N7 (not documented in 20 years)
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How is EIV transmitted?
inhalation of aerosols, fomites- HIGHLY contagious
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What population of horses are most affected by EIV?
2 year olds at a racetrack
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What is often sequelae to EIV infection?
serious secondary bacterial infection (ciliated respiratory epithelium denuded)
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In what populations is EIV fatal? (3)
naive populations, donkeys, neonates born to unvaccinated dams
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EIV initiates the _________, which leads to rapid spread throughout the __________.
lytic replication cycle; respiratory tree (LRT)
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EIV has a(n) _________ incubation period; clinical signs include... (4)
short; fever, dry hacking cough, serous oculonasal d/c, regional lymphadenopathy
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What secondary bacterial infections occur with EIV?
bronchopneumonia most serious, but all levels of respiratory tree can be affected
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How do you diagnose EIV?
clinical signs, outbreak/multiple horses affected, [acute] nasal swab for PCR
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Treatment for EIV. (6)
rest/3-4 weeks off even if they look fine, ventilation, NSAIDs, soft diet, monitor/treat secondary bacterial infections, +/- amantadine/rimantadine (antivirals)
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How can you prevent EIV outbreaks?
vaccination!- modified live intranasal
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Unique to EIV, when should first vaccination occur?
6-9 months old b/c vaccinating too early might make them anergic against future vaccinations (hyporesponders)
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What is the main primary respiratory bacterial pathogen in adult horses?
Strep equi
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What is the result secondary (opportunistic) respiratory bacterial pathogen in adult horses?
septic pleuropneumonia
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What is the main respiratory bacterial pathogen in weanling foals?
Rhodococcus equi
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What animals are susceptible to Strep equi?
any equids who haven't already had it (protective immunity)
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In an outbreak of Strep equi, what role to immune horses play?
do not develop infection but can serve as asymptomatic carriers/ transmit disease
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Why "should" strangles be easy to eradicate? (3)
only colonizes equids, fever occurs ~48 hrs before they nasally shed organism (can isolate infected animals prior to transmission), easy to kill in environment
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Even though strangles should be easy to eradicate, why isn't it? (3)
asymptomatic carriers, organism shed 3-4 weeks post-recovery, intermittent shedding may persist for months to years
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How do you ID an asymptomatic carrier of strangles?
gutteral pouch lavage with saline, catch it as it flows out of the horse's nose (through eustachian tube) [endoscopy]-->bacterial culture and PCR
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What populations are at low, medium, and high risk populations for strangles?
- Low: closed populations that do not travel
- Medium: closed populations that travel
- High: open populations (frequent mixing/new arrivals)
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Describe the pathogenesis of strangles. (4)
adhesion to respiratory epithelium--> invasion of lamina propria--> entry into lymphatic--> evasion of phagocytosis
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What lymph node chains are most likely to be affected with strangles? (2)
submandibular lymph nodes, retropharyngeal lymph nodes
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How does strangles lead to gutteral pouch empyema?
rupture of retropharyngeal ln dorsally into gutteral pouch
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What surface protein is measured as a titer in some non-typical cases of strangles?
M protein
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How do we diagnose acute strangles? (3)
bacterial culture (nasal swab, nasopharyngeal lavage, ln aspirate), PCR, serology- serum M protein titer (most sensitive)
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What should you do before vaccinating a horse for strangles and why?
test M protein titers; vaccination is contraindicated in animals with high M protein titers because it can lead to immune reaction/ purpura hemorrhagica
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How do you treat strangles? (3)
supportive care, quarantine, +/- penicillin (if severe, tracheostomy if can't breathe, metastatic abscessation, purpura hemorrhagica)
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What are potential complications of strangles? (5)
URT obstruction (tracheostomy asap!), gutteral pouch empyema, immune-mediated purpura hemorrhagica/ myositis, metastatic abscessation (bastard strangles), membranous glomerulonephropathy
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What is purpura hemorrhagica?
immune-mediated vasculitis, type III hypersensitivity a few weeks after recovering from strangles or post-vaccination (high serum M protein titer)
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How do you treat purpura hemorrhagica? (3)
penicillin, immunosuppressive doses of dexamethasone, supportive care
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How can you deem a carrier "clean"?
three negative gutteral pouch lavages at weekly intervals [expensive]
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How can you prevent strangles? (2)
inactivated M protein derivative vaccine, modified live intranasal strangles vaccine
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When are foals infected with Rhodococcus?
EARLY- within the first 7-10 days of life
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What is the most important virulence factor of Rhodococcus?
VapA gene
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What disease is most commonly caused by Rhodococcus in weanling foals?
pyogranulomatous bronchopneumonia
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What disease is most commonly caused by Rhodococcus in adult horses?
immune compromise
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What is a public health concern associated with Rhodococcus equi?
people with AIDS can get severe disease caused by R. equi
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Clinical signs of R. equi in foals.
fever, +/- cough, +/- nasal d/c
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How do you diagnose R. equi in foals?
trans-tracheal wash for bacterial culture [definitive], radiographs are suggestive
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What is the classic radiographic lesion in foals with R. equi?
cotton ball abscesses- pyogranulomas- consolidations
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How do you treat R. equi in foals? (2)
macrolide antimicrobial (erythromycin, Clarithromycin, Azithromycin) in combination with Rifampin [continue until normal thoracic rads, normal bloodworm, normal foal]
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Foals do not ________ when they are on a macrolide; therefore...
sweat; can lead to hyperthermia (do not exercise, house in cool, shaded area)
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How can you prevent R. equi? (6)
lower stocking density, avoid dirt lots for neonates, hyperimmune plasma for prophylaxis, screening, prophylactic macrolides (yikes.....not recommended)
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Equine shipping fever is _____________.
septic bacterial pleuropneumonia
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What are risk factors for pleuropneumonia? (8)
distance travel, heads tied up during transport, insufficient time with head lowered during breaks (mucociliary elevator), viral disease (esp. influenza), stress/immunosuppression, racehorses, poor dentition/choke, general anesthesia
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What organisms are associated with equine pleuropneumonia? (4)
Strep equi subsp zooepidemicus, Actinbacillus equuli, Anaerobes, +/- coliforms
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Clinical signs of pleuropneumonia. (5)
fever, tachypnea, purulent hemorrhagic nasal d/c, anorexia, injected MMs
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How do you diagnose pleuropnemonia? (3)
trans-tracheal wash for culture, +/- thoracocentesis for culture [TTW more important], US chest
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How do you treat pleuropneumonia? (6)
thoracic drainage (thoracocentesis), broad spectrum antibiotics (penicillin, gentamicin, metronidazole), fluids, NSAIDs, laminitis prophylaxis, respiratory support
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Complications associated with pleuropneumonia. (6)
laminitis, thrombophlebitis, pleural adhesions, thoracic abscess, cachexia, cellulitis near chest tube
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The most common non-infectious lower airway disease of horses.
recurrent airway obstruction (Heaves, RAO)
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In what horses does RAO occur?
10-15 year old horses in the northern hemisphere with moist, cool climates
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Describe the pathophysiology of RAO.
inhale particulates--> inflammation of airway d/t hypersensitivity to inhaled molds/organic dusts--> elaboration of cytokines in airways--> neutrophil chemoattraction and influx
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What are the 3 most important pathologies associated with RAO?
neutrophilic airway inflammation, bronchoconstriction/increased airway reactivity, mucus production
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What are the end pathophysiologic results of RAO? (4)
small airway obstruction, expiratory small airway collapse, peripheral air trapping, hypoxemia
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What are clinical signs of RAO? (5)
[episodic and progressive] cough at work and when fed, expiratory effort, nostril flaring at rest, nasal d/c, exercise intolerance
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How do you definitively diagnose RAO?
bronchoalveolar lavage for fluid cytology >20% non-degenerate neutrophils
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How do you environmentally manage RAO? (6)
put the horse outside all the time, stalls near end of barn/away from hay storage (if can't be outside all the time), low particulate bedding options/wet down bedding, low particular forage, wet down feed/ hay steamer, DON'T feed round bale hay/moldy shit
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What drugs are used to manage RAO? (4)
corticosteroids (prednisolone, dexamethasone), [bronchodilators] beta 2 agonists (albuterol, clenbuterol), muscarinic antagonists (atropine, glycopyrrolate); topical (inhaled) corticosteroids and bronchodilators
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Exercise-induced pulmonary hemorrhage (EIPH) usually affects...
young athletes/ racehorses
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Risk factors for EIPH.
breed (Tbs and STBs) and speed
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What causes EIPH?
alveolar capillary rupture with consequent extravasation of blood into the pulmonary alveoli and interstitium
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How do you diagnose EIPH? (3)
visual inspection, tracheobronchoscopy within an hour or 2 of work, bronchoalveolar lavage shows RBCs, Erythrophages, hemosiderophages
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What drug is used to manage EIPH?
furosemide (also performance enhancing in horses that are not bleeders...)
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Clinical findings with URT obstruction. (4)
inspiratory stridor, tachypnea, sweating, anxiety
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What is the treatment for URT obstruction?
tracheostomy tube!!!!!!! ASAP, treat underlying condition
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