Equis ISSN 2398-2977

Conjunctivitis: bacterial

Contributor(s): Dennis E Brooks, Graham Munroe

Introduction

  • Incidence: a common cause of conjunctivitis.
  • Cause: usually a secondary infection of commensals or pathogens following primary damage to conjunctiva;Moraxella equican cause a primary infection.
  • Signs: typical clinical signs of conjunctivitis   Conjunctivitis: overview  ; increased mucopurulent/purulent ocular discharge.
  • Diagnosis: bacterial culture and sensitivity testing are essential - particularly if the infection fails to respond to broad spectrum antibiotics in 5-7 days.
  • Treatment: removal of primary cause +/- treatment; topical antibiotics; fly control measures are important inMoraxellainfections.
  • Prognosis: good - most respond to treatment within 5-7 days.

Pathogenesis

Etiology

Primary infections
  • Moraxella equi.

Systemic infections

Secondary invaders

Pathophysiology

  • Bacteria are present in the conjunctival sac of most horses (commensals) - their presence alone does not indicate an infectious process   Eye: microbiology - overview  .
  • The microbial population of the conjunctival sac of horses with ocular surface disease does differ from that of the normal animal   Eye: microbiology - overview  . Gram positive bacteria are found in normal horses and gram negative bacteria in diseased horses.
  • Most bacteria act as secondary opportunists following primary damage to the conjunctiva - pathogens or commensals.
  • Specific primary infections includeMoraxella equi.
  • A few systemic bacterial infections can   →   eye infections involving the conjunctiva.
  • Most common form of bacterial conjunctivitis: primary insult   →   secondary invasion of pathogenic or opportunitic commensal bacteria   →   greater proportion of Gram negative organisms isolated than from normal eyes.
  • Moraxella equiis only pathogenic for horses - has been isolated as a cause of primary bacterial conjunctivitis particularly in USA.
  • Strangles (Streptococcus equi  Streptococcus spp  ) is recorded as causing a bilateral serous   →   purulent conjunctivitis sometimes in association with uveitis   Uveitis: anterior - overview  .
  • Other severe systemic infections may   →   loss of weight, dehydration and enophthalmos   →   conjunctival irritation and inflammation.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications


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