Bacterial Diseases

Question 1

most important bacterial diseases for horses

Answer 1

▪ Streptococcus equi subsp. equi
▪ Sequelae of Strep equi subsp. equi
▪ Bacterial pneumonia

Question 2

Streptococcus
equi subsp equi
- what type of bacteria is this? what common disease does it cause?

Answer 2

▪ Gram + B-hemolytic coccoid
▪ Primary pathogen
▪ Causative agent of Strangles
> Very common infectious disease
> Highly contagious

Question 3

Strep equi subsp equi
▪ Epidemiology, morbidity, mortality, transmission?

Answer 3

▪ Most common in 1-5 year olds
▪ Naïve populations
> Morbidity= 100%
> Mortality= 10%
<><><><>
Transmission
▪ Nasal and abscess discharge
▪ Shedding for 4-6 weeks post-infection (intermittent)
▪ Asymptomatic carriers

Question 4

Strep equi subsp equi
▪ Pathogenesis

Answer 4

▪ Adheres to epithelial cells
▪ Translocates across basement membrane
▪ Enters local lymphatics and lymph nodes
> Replicates extracellularly
> Attracts large numbers of neutrophils
▪ Lymph node abscessation
> 10-14 days post-infection

Question 5

Strep equi subsp equi
▪ Clinical signs

Answer 5

▪ Fever
▪ Lethargy
▪ Inappetance
▪ Hyperemic mucous membranes
▪ Serous- mucopurulent nasal discharge
▪ Serous- mucopurulent ocular discharge
▪ Lymphadenopathy > Rupture in 7-14 days

Question 6

what is strangles? signs? length?

Answer 6

Strep equi subsp equi > lymphadenopathy sequelae
▪ Stridor
▪ Dysphagia
▪ Respiratory distress
▪ Rupture into guttural pouch
▪ Neuropathy
▪ Empyema
▪ Chondroid formation
<><><><>
Disease course
▪ 23 day average

Question 7

Strangles diagnosis

Answer 7

▪ Clinical signs
▪ Culture or PCR
> Nasopharyngeal lavage
> Guttural pouch lavage
▪ Upper airway endoscopy

Question 8

structures in the medial compartment of the guttural pouch

Answer 8

▪ Internal carotid artery
▪ Cranial cervical ganglion
▪ Cranial sympathetic trunk
▪ Glossopharyngeal nerve
▪ Vagus nerve
▪ Accessory nerve
▪ Hypoglossal nerve

Question 9

important structures in the lateral guttural pouch compartment

Answer 9

▪ Maxillary artery
▪ External carotid artery
▪ Facial nerve (VII)
▪ Mandibular branch of the trigeminal nerve

Question 10

Strep equi subsp equi
▪ Treatment

Answer 10

▪ Supportive care
> Anti-inflammatories
▪ Abscess care
> Hot packing
> Lancing
> Lavage
▪ Guttural pouch
> Lavage
> Instillation of penicillin gel
<><><><>
- mostly do not need antimicrobials

Question 11

Strep equi subsp equi
▪ When to use antimicrobials?
- sequelae?

Answer 11

▪ Acutely and severely affected
> Prior to abscess formation
▪ Respiratory distress
<><><><>
Carriers (usually do not need systemic antimicrobials)
▪ In conjunction with local therapy
<><><><>
Sequelae of antimicrobial use
▪ Metastatic abscesses
▪ Purpura hemorrhagica
▪ Delayed disease progression

Question 12

strangles outbreak management
- goals and actions

Answer 12

▪ Primary goal
> Immediately quarantine the property
▪ Establish isolation area on property
▪ Establish cleaning and handling protocols
▪ Perform endoscopy on all horses
> Apparently healthy
> Affected
▪ Collect nasopharyngeal lavages from all recovering horses
> 3 negative samples in a row

Question 13

strangles prevention

Answer 13

▪ Quarantine new arrivals > 3 weeks
▪ Screening
> Guttural pouch endoscopy, Culture +/- PCR
> Nasopharyngeal lavage
> Serology: Does not indicate active infection, Use with caution
▪ Excellent biosecurity

Question 14

vaccination for strangles
- who not to give?
- types

Answer 14

▪ DO NOT vaccinate recently infected horses
▪ DO NOT vaccinate when SeM ≥ 1:3200
▪ Extract vaccine > Decreases risk by 50%
▪ Attenuated live vaccine > Intranasal

Question 15

Strep equi carriers
- how many? who are the carriers?
- how long? what forms?
- diagnosis?

Answer 15

▪ ~ 10% of horses in an outbreak
> Fail to clear infection
▪ ~40% of horses positive @ 40 days
> Median duration= 60 days
▪ Persists for months to years
> Empyema
> Chondroids
▪ Diagnosis
> Culture or PCR

Question 16

Strep equi carriers
▪ Treatment

Answer 16

Empyema
▪ Repeated lavage
▪ Penicillin gel
▪ Acetylcysteine
<><><><>
Chondroids
▪ High-volume lavage
▪ Acetylcysteine
▪ Endoscopic-guided
▪ Surgical intervention

Question 17

Metastatic abscesses from strep equi equi
- what are these? how common?
- clinical signs?

Answer 17

• bastard strangles - spread throughout body
  ▪ ~ 2-20% of cases
  ▪ Exact pathogenesis unknown
  <><><><>
  Clinical signs:
  ▪ Fever
  ▪ Lethargy
  ▪ Inappetance
  ▪ Weight loss
  ▪ Organ system specific

Question 18

Metastatic abscesses (bastard strangles) diagnosis, treatment, prognosis

Answer 18

Diagnosis:
▪ SeM titer >1:12,800
▪ Abscess on advanced imaging
<><><><>
Treatment:
▪ Supportive care
▪ Surgical intervention
▪ Long-term antimicrobials
<><><><>
Prognosis:
▪ Mortality rate = 62%

Question 19

Purpura Hemorrhagica
- cause? how common?
- risk factors
- what is this?

Answer 19

• strep equi equi: 6-7% of cases
  <><><><>
  Risk factors
  ▪ Re-exposure to bacteria
  ▪ Vaccination
  ▪ 2-4 weeks post infection
  ▪ SeM serum titer >1:3200
  <><><><>
  ▪ Type III immune-mediated hypersensitivity reaction > because they have a lot of antibody already

Question 20

Purpura Hemorrhagica clinical signs

Answer 20

“cellulitis on all four limbs” is what we often hear from clients
<><><><>
▪ Fever
▪ Tachycardia & tachypnea
▪ Reluctance to move
▪ Edema
> Limbs, head, ventrum
> Serum exudation→ ulceration
> Skin sloughing
▪ Petechia and ecchymosis
▪ Colic or diarrhea
▪ Cardiac arrhythmias
▪ Renal failure
▪ Muscle infarction

Question 21

Purpura Hemorrhagica
▪ Diagnosis

Answer 21

▪ History and clinical signs
▪ Skin biopsy (not really a great idea as it can take a long time to heal)
> Leukocytoclastic vasculitis
▪ SeM titer > 1:12800

Question 22

Purpura Hemorrhagica
▪ Treatment, mortality rates

Answer 22

Limbs
▪ Hydrotherapy
▪ Bandaging
<><>
Systemic
▪ Corticosteroids > immunosuppressive
▪ Non-steroidal anti-inflammatories
▪ Antimicrobials > if you think they still have an active infection, which they may not!
▪ Intravenous fluid therapy
<><>
▪ Mortality rate= 5-7 %

Question 23

Immune-mediated myositis
- who gets it?
- associations / triggers?
- clinical signs?

Answer 23

▪ Quarter horses
▪ < 8 or >17 years
<><><><>
40% associated with trigger
▪ Strep equi
▪ Vaccination
▪ Respiratory virus
<><><><>
Clinical signs
▪ Muscle atrophy
▪ Stiffness & malaise
▪ Weakness & recumbency

Question 24

Immune-mediated myositis
▪ Diagnosis, treatment, prognosis

Answer 24

Diagnosis
▪ Genetic testing
▪ Muscle biopsy > Epaxial or gluteal
<><>
Treatment
▪ Corticosteroids
> 1 month
<><>
Prognosis
▪ Full recovery possible
▪ 50% recurrent episodes

Question 25

bacterial pneumonia in horses - pathogenesis in general

Answer 25

Disruption of host defenses
▪ Mucociliary elevator dysruption
▪ Immunosuppresion
▪ Bypass of upper airway
▪ Pre-existing inflammation
<><><><>
▪ Colonization of airways
▪ Extension into parenchyma

Question 26

most common agent causing bacterial pneumonia in the horse?

Answer 26

strep zooepidemicus

Question 27

Bacterial pneumonia
▪ Clinical signs

Answer 27

Clinical signs
▪ Fever
▪ Inappetence
▪ Lethargy
▪ Coughing
▪ Nasal discharge
▪ Tachypnea
▪ Increased respiratory effort
▪ Respiratory distress
▪ Weight loss

Question 28

Bacterial pneumonia
▪ Diagnosis

Answer 28

▪ Physical examination
▪ Thoracic ultrasound
▪ Thoracic radiographs
▪ Endoscopy
▪ Culture and sensitivity

Question 29

Bacterial pneumonia
▪ Treatment

Answer 29

▪ Antimicrobials > Based on sensitivity
▪ Anti-inflammatories
▪ Intravenous fluids
▪ Supportive care
▪ Correct underlying condition

Question 30

possible sequelae of bacterial pneumonia

Answer 30

▪ Pleuropneumonia
▪ ARDS
▪ Laminitis
▪ Septicemia