Equine Ubiquitous Infections - Strangles Flashcards
what is the bacteria that causes strangles
Streptococcus equi ss equi
how is strangles transmitted
direct contact with infected cause usually
what are the risk factors for strangles
Co-mingling, horse movement
Poor specific immunity
Asymptomatic carrier horses
what is the incubation period of strangles
3-4 days
depends on exposed dose may be much longer (3-14 days)
what is the pathogenesis of strangles
Nasopharyngeal mucosal hyperemia followed by intranodal abscessation
- Spread to draining lymph nodes (hours)
- Bacterial multiplication, PMNL infiltration
- Lymphoid necrosis and lymphadenopathy
May be eventual LN rupture
- Local complications in ~20% of cases
- Purulent sinusitis, perioorbital abscessation, facial cellulitis
- Cranial nerve damage: laryngeal paralysis, facial paralysis, Horner’s syndrome
Aspiration of nasopharyngeal exudate
Occasional pleuropneumonia
what is the first sign of strangles infection
pyrexia 39.9-40C
what are the subsequent clinical signs of strangles
Inappetence
- Pharyngeal inflammation
- Cranial nerve dysfunction
Lethargy
Nasal discharge (serious —> purulent)
Lymphadenopathy
May cough, often not
Mild signs only in horses with immunity
LN abscessation variable
Most cases much better by 3-5 days after start of clinical signs
May progress to LN rupture which prolongs course of disease
- Skin
- Guttural pouch
Retropharyngeal LN enlargement may compress dorsal pharynx
Stertorous breathing due to restricted airflow
what are less common clinical signs of strangles
Excessive retropharyngeal LN enlargement or guttural pouch distention
- Increased pharyngeal compression
Reduced air movement at nostrils
when does bacterial shedding occur in uncomplicated cases and how long does it last
2-3d after fever onset
persists for 2-3 weeks in most animals
systemic + mucosal immune responses evident 2-3 weeks post infection
if the guttural pouch is infected how long does infection last
infection is usually cleared from guttural pouches within 6 weeks
what % of horses develop solid immunity after recovery from strangles
75%
how is strangles diagnosed in uncomplicated cases (5)
- Clinical signs
- Direct aspiration from LN and culture
- Nasal swab in media acceptable if discharging
- Nasopharyngeal swab required if no nasal discharge
- Saline lavage of guttural pouches
- Culture/PCR has improved sensitivity
- ELISA for antibody to specific cell wall antigen useful screening test — paired titres best at 3 weeks
***Note exposure vs. active infection!
if the culture is positive and the PCR is positive how do you interpret the results of a nasopharyngeal swab
the animal is infected
if the culture is positive and the PCR is negative how do you interpret the results of a nasopharyngeal swab
the animal is infected
if the culture is negative and the PCR is positive how do you interpret the results of a nasopharyngeal swab
animal is infected
if the culture is negative and the PCR is negative how do you interpret the results of a nasopharyngeal swab
animal is not infected?
what is the strangles blood test
Antibody production to two antigens
Measures the response using cutoff points
how do you interprete ELISA
Paired serology requires re-testing of sample 2 against sample 1
Inter assay variation
- Results and re-test +/- 0.3
Valid comparison ONLY between samples tested as pairs ex. A to A, B to B and C to C
First sample ideally taken 2 weeks after time of first exposure
how are uncomplicated cases of strangles treated
Anti-inflammatories to reduce temperature
Hot packing of LNs to promote maturation
- Lance and drain
Usually no antibiotics unless very unwell as may prolong duration
- Penicillin G is antibiotic of choice >22,000 IU/kg
- Reserved for refractory/severe cases only
OR
- Use at first sign of pyrexia
Nursing care
- Soft feeds
- Management of abscessation
what is purpura hemorrhagica
Leukocytoclastic vasculitis seen in 1-2% cases
circulating IgA and M protein immune complexes deposited on vessel walls
complement activation
- Polymorphonuclear leukocytes (PMNL) recruitment and lysosomal enzyme damage to vessels, causing increased permeability
- Commoner if higher antibody titres
- If high at time of exposure more likely to develop this condition
- Maximal at 2-4 weeks post infection
- Delayed clinical manifestation
- Ideally assay IgA prior to considering vaccination
what are the clinical signs of purpura hemorrhagica
Petechial haemorrhages
Stiffness and reluctance to move
Edema of ventral abdomen, prepuce and legs
Hot, painful swelling, with sharp demarcation (‘stove pipe’ edema)
how long does recovery take from purpura hemorrhagica
Recovery in 7-10 days or progression:
- Widespread edema of head and respiratory tract with petechiation of mucus membranes
- Skin necrosis with serum release
- Progressive lung edema, neurological signs, death
- Up to 50% mortality
how is purpura hemorrhagica treated
Removal of antigenic stimulation
Penicillin (>25,000 IU/kg QID)
Corticosteroids if petechiation develops (prednisolone 0.5-2 mg/kg SID per os)
Wound care and bandaging of extremities
Hematinic agents may aid correction of chronic anemia
Intensive nursing
Guarded prognosis
- Particularly for first 3 weeks after onset of clinical signs
what is a possible sequela
disseminated abscessation or ‘bastard strangles’
what is disseminated abscessation or bastard strangles
Mediastinal or mesenteric LN involvement most common
Compression of esophagus
Distention of jugular vessels, could rupture and cause pleural pneumonia
Liver, kidney, spleen, synovial membranes or brain may be involved
what are the clinical signs of bastard strangles
Chronic weight loss
Recurrent colic
Adhesions
Recurrent peritonitis
CNS depression
May involve <10% cases
Clinical signs depend on site of involvement
what can the guttural pouches become involved in infection
Inflammation of guttural pouch lining common
Purulent discharge from retropharyngeal LN into pouch may occu
how long does guttural pouch empyema occur
Guttural pouch empyema mostly short lived
what does guttural pouch empyema cause
Causes dysphagia and inspiratory stridor
Chronic empyema develops in up to 10% of animals
Eventual inspissation of pus —> chondroid formation
Asymptomatic carriers! Intermittent lifelong shedding
how can a horse become a chronic shedder
chondroids in the guttural pouch
shedding intermittently from nasal mucosa
how are guttural pouch emypemas treated
Drainage and lavage (water, saline, ringers) via indwelling Foley catheter or Mild guttural pouch catheter
Instillation of gelatin/penicillin G mixture:
- Prolonged action
Systemic antibiotics:
- Procaine penicillin >25,000 IU/kg IM BID
- Oral TMPS 20mg/kg BID
- Prolonged treatment required
how are chondroids treated
Most chondroids can be removed via endoscope
- Helical basket snap or simple snare
Multiple chondroids may require surgical removal
Standing approach possible
Site usually left open as contaminated wound
Subsequent lavage and treatment of pouch as for empyema
- Culture/PCR required after minimum of 3 weeks to determine success of treatment
what are important control points of strangles
Shedding does not start until 1-2d after pyrexia
Nasal shedding present for >2-3 weeks in most animals
Persistent guttural pouch infection may cause intermittent shedding for years
Incubation period variable depending on dose received
Mild disease only in previously recovered animals
how would you control an outbreak of strangles
- Prompt isolation and ID of pathogen
- ID infected, exposed and unexposed horses
- Red, amber and green groups
- Quarantine
- Prevent horse movement on/off premise
- Strict hygiene principles
- Bacteriological screening of convalescing and exposed horses
- Investigate and treat carrier horses
- Vaccination?
how effective is the stranlges vaccine
limited efficacy
is it recommended to vaccine in the face of an outbreak
questionable
when is recommended to vaccinate against strangles
Most appropriate for high-risk horses
Yards where isolation impossible
Yards with endemic Strangles
Booster intervals to be decided
describe how you would vaccinate low risk, medium risk and high risk horses
what are high risk horses for carrying strangles
New horse incubating disease
- Especially from dealers premise
Recovered clinically but infectious
- Subclinical S. equi carriers
Older horses with existing immunity
- Milder disease syndrome
True long-term asymptomatic carriers
- Guttural pouch empyema
- Chondroids
- Intermittent shedders
- Metastatic involvement
- Variant S. equi strains
describe how you would control a strangles outbreak on a livery yard
Isolate new horses, ideally for 21 days
Look for signs of previous infection
- Scarring, thickening over parotid region
Monitor for clinical signs
Consider blood sampling +/- swapping or scoping to pick up carrier cases
- Then possible vaccination
Isolate any horse with a high temperature (temp 2x daily)
Confirmed cases are moved away from premises, subsequent samples are submitted for PCR/culture >6 weeks after clinical signs stopped
Carrier horses ID’d and isolated
All blood sample positive cases confirmed negative for shedding on guttural pouch endoscopy
Paired antibody titres collected from horses with original positive sample
Yard allowed to open 8 weeks after first case (no new clinical signs for >6 weeks, cessation of shedding, clearance of carrier horses)
