Lower respiratory tract disease in groups of horses

Question 1

What are some infectious respiratory diseases in horses?

Answer 1

• Influenza
• Equine herpes virus 1+4
• Rhodococcus equi
• Streptococcus equi var equi

Question 2

When would you suspect infectious respiratory disease?

Answer 2

• Bilateral nasal discharge (unilateral usually in front of nasal septum + non-infectious)
• Pyrexia
• Cough, enlarged lymph nodes, anorexia
• Individual vs group affected
• Vaccine Hx
• Travel Hx

Question 3

How would you confirm infectious disease?

Answer 3

• Culture / PCR / virus isolation
• Antibodies (ELISA)

Question 4

What is the pathogenesis of influenza?

Answer 4

• Aerosol transmission (direct / indirect)
• Enters URT + replicates
• Viraemia
• Destroys mucocilliary tract
• secondary pneumonia

Question 5

What is the epidemiology of influenza?

Answer 5

• Spread up to 1-2km (8km in wind)
• V short incubation
• Low mortality
• Vaccination not 100% effective

Question 6

What is the most common strain of influenza?

Answer 6

• H3N8

Question 7

What are typical clinical signs of influenza?

Answer 7

• Pyrexia
• Harsh dry cough
• Nasal discharge - serous initially, mucopurulent with 2ndary bacterial infection
• Submandibular LN may be normal
• Milder in vaccinated animals

Question 8

How is influenza diagnosed?

Answer 8

• Nasopharyngeal swab - RT-PCR
• Serum sample - antibody titre

Question 9

How would you treat influneza?

Answer 9

• Supportive care
• NSAIDs
• Anti-microbials if 2ndary infection
• Rest for 2 weeks minimum
• Vaccinate in face of outbreak

Question 10

How would you control influenza?

Answer 10

• Isolate
• Movement restrictions
• Biosecurity - quarantine + disinfection
• Vaccination

Question 11

Why would a vaccine not be effective?

Answer 11

• Strain
• Timing - Ab dip towards end of vaccine lifespan
• Uptake
• ‘non-responders’

Question 12

What are the different types of equine herpes virus?

Answer 12

• EHV-1 : Respiratory disease, neurological disease, abortion (sudden death in foals).
• EHV-2 : Keratoconjunctivitis
• EHV-3 : Equine Coital Exanthema
• EHV-4 : Respiratory disease (& abortion)
• EHV-5 : Equine Multinodular Pulmonary Fibrosis

Question 13

What is the pathogenesis of EHV 1+4?

Answer 13

1. aerosol spread (direct / indirect)
2. nasal inoculation + replication in URT epithelium
3. EHV 4 = local infection (rhinopharyngitis/ tracheobronchitis)
   EHV 1 = migration to systemic infection - viraemia, vasculitis, microthrombosis + infarction, ataxia + abortion

• Latency = carriers for life

Question 14

What are clinical signs of EHV 1+4?

Answer 14

• Respiratory - EHV4 more common in respiratory outbreaks
  -biphasic fever (mild)
  -bilateral nasal discharge
• enlarged submandibular LNs
• +/- cough
• Abortion / stillborn / neonatal death
• Neuro disease (EHV 1)

Question 15

How is EHV diagnosed?

Answer 15

• Nasal swab - PCR / virus isolation
• Blood samples - check WBCs
• PM

Question 16

How is EHV treated?

Answer 16

• No Tx required
• Rest
• NSAIDs?

Question 17

How is EHV controlled?

Answer 17

• Reduce shedding + exposure
• Vaccination + biosecurity
• do not vaccinate in outbreak

Question 18

What is the pathogenesis of Rhodococcus equi?

Answer 18

• Nasal inoculation - replicates in infected alveolar macrophages
• Causes pyogranulomatous bronchopneumonia
• Shed in respiratory secretions + manure

Question 19

What is the epidemiology of r. equi?

Answer 19

• Most common cause of pneumonia in foals (<2w/o)

Question 20

What are clinical signs of R.equi?

Answer 20

• Pulmonary - multifocal pulmonary abscesses, high RR + pyrexia
• Extra-pulmonary - uveitis, septic arthritis, IMPA, enterocolitis, abscessation anywhere
• General - weight loss, poor growth rates

Question 21

How is R. equi diagnosed?

Answer 21

• Farm history
• Bloods - generalised inflammation
• Ultrasonography - score lesions (only treat if over 10 lesions >1cm)
• Radiography
• Transtracheal aspiration - cytology

Question 22

How would you treat R.equi?

Answer 22

• Don’t treat every foal - sub-clinical will resolve
• Macrolide + rifampin

Question 23

Whats important about macrolide use?

Answer 23

• Fatal colitis in mares - only use in foals
• Wipe foals muzzle after tx + keep in shade

Question 24

How would you control R.equi?

Answer 24

• Administer R.equi hyperimmune plasma to foals
• NO vaccines
• Reduce stocking density

Question 25

What are clinical signs of Strep. equi?

Answer 25

* Pyrexia + inappetence (24-48hrs) * Bilateral mucopurulent nasal discharge * Lymphadenopathy * LN abscessation * Dyspnoea * Dysphagia * lead to bastard strangles, purpura haemorrhagica, myositis

Question 26

How is Strep equi diagnosed?

Answer 26

- identify active disease * Nasopharyngeal swabs - PCR + culture * GP lavage (>48hrs) - PCR + culture * Aspiration of LN abscess - PCR + culture

Question 27

How is Strep equi diagnosed? - identify carriers

Answer 27

* Nasophanryngeal swabs - 3 times 1 week apart - PCR + culture * GP lavage - gold standard - PCR + Culture

Question 28

How is strep equi treated?

Answer 28

* Penicillin * NSAIDs * Supportive Tx * Lance abscess * Tracheostomy if severe dyspnoea

Question 29

How would you control strangles?

Answer 29

* Early isolation of pyrexic animals * Traffic light system - exposure risk * Yard closed until clear * Biosecurity * 3 weeks after active cases identify carriers / PI

Question 30

How would you prevent strangles?

Answer 30

* Yard strategy * Biosecurity * Quarantine * Isolate * Vaccine? doesn't work too well - consider for high risk

Question 31

What is the 2nd most common cause of poor performance after muscoskeletal?

Answer 31

* Mild asthma / inflammatory airway disease - prevalence - 11-50% based on mucopus in trachea

Question 32

What are risk factors for mild-asthma?

Answer 32

* Co-mingling * Exercise - strenuous exercise * Transport * Age - young * Stable environment - poor ventilation + bedding