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