Strangles/streptococcus equi infection
key points
highly contagious (morbidity 30-100%)
chronic sequelae are common
complications in 20% cases
potentially fatal (mortality can reach 10% in some outbreaks)
10% of recovered animals become chronic carriers
dx, tx and monitoring can be expensive
outbreaks can be crippling for business
bacteriological cure of recovered cases cannot be 100% certain
Pathogenesis
infection occurs via the pharyngeal tonsil and associated lymphoid tissue following nasal or oral entry
organisms rapidly translocate to draining lymph nodes --> multiply --> lymphadenopathy with surrounding oedema within 7-10 days
abscessation of submandibular, parotid and retropharyngeal lymph nodes
nasal shedding of bacteria begins 2-7 days post-infection
usually after onset of pyrexia
persists for 2-3 weeks
epizootiology
direct nose, mouth or close aerosol contact spread or indirect famine contamination with purulent discharges
clinical disease
incubation period of 2-10 days --> animals present acutely and may have dull demeanour and be partially anorexic with a fever
lymph node abscessation
yellowish seromucoid nasal discharge often precedes a purulent discharge
tenderness and slight swelling of the submandibular and retropharyngeal regions may progress to obviously painful, indurated oedema
head and neck slightly extended due to pharyngeal discomfort
pain, pharyngitis and progressive lymph node abscessation
can cause coughing, dysphagia, starter and respiratory distress
if ruptured --> discharging pus
Diagnosis
bacteriological swabs from draining abscesses or if absent the nasopharynx
pass long nasopharyngeal swabs via the ventral meatus and encourage swallowing to allow release of any discharge from the guttural pouches
mild/chronic cases
transendoscopic guttural pouch lavages and submit for culture and PCR
Treatment
individual uncomplicated cases
isolate
NSAIDs e.g. phenylbutazone
improve demeanour and reduce fever
parachute cases --> antibiotics
once any evidence of lymphadenitis is present antibiotics should be avoided and antiphlogistics e.g. hot packs and topical icthamol should be used to encourage abscesses and point rupture to facilitate surgical drainage
following abscess rupture --> family flushing with dilute antiseptics promotes healing
nursing considerations: fresh water, palatable feed, comfortable stable environment
herd outbreaks
isolate all!
manage affected horses and in contact horses should have their rectal temp monitored daily and or receive antibiotics
separate equipment, clothing and see in ascending order of risk
screen as negative on basis of 3 nasopharyngeal swabs at 3-7 day intervals or bilateral guttural pouch lavage prior to release from isolation
culture and PCR from pooled bilateral transendoscopic guttural pouch lavages
most recover uneventfully over 4-6 weeks following drainage of affected lymph nodes and the development of immunity
Complications
associated with persistent guttural pouch infection, metastatic abscessation or immune-mediated disease
indications for use of antibiotics in cases of strangles
per acutely affected animals <24h pyrexia/off colour
prophylactic treatment of unaffected in contact animals
critical cases with life-threatening airway obstruction
cases of purport haemorrhagica and concurrent bacterial infection
treatment of internal/disseminated abscesses in cases of bastard strangles
adjunctive therapy of guttural pouch empyema
treatment of thoroughly investigated chronic carriers
severe nasopharyngeal compression
local lymphatic abscessation
guttural pouch empyema
presentation: persistent purulent nasal discharge, swelling in the throat latch area, dyspnoea, dysphagia, inspiratory noise at exercise or may show no clinical signs
radiographs/endoscope
uni or bilateral nasopharyngeal compression, fluid +/- chondroid accumulation and gross distortion or enlargement of pouches
Bastard strangles
drainage and lavage!
metastatic abscessation to remote sites can produce signs localised to affected organ/body system
thoracic or abdominal abscessation --> septic pleuropneumonia or peritonitis - pneumonia
mesenteric LN abscessation
weight loss, intermittent pyrexia and colic
due to secondary adhesion formation or intestinal obstruction
anaemia
usually anaemia of chronic disease due to bone marrow suppression by bacterial toxins
purpura haemorrhagica
subcutaneous oedema
petechiae or ecchymoses on visible mm
recent history of infection with bacterial or viral pathogens
histopathological evidence of leucocytoclastic vasculitis on skin biopsy
other immune mediated disease
chronic subclinical carrier state