Moraxella bovis


Overview

  • Moraxella bovis causes infectious bovine keratoconjunctivitis
  • Found on mucous membranes of carrier cattle
  • Susceptible to desiccation therefore short survival in environment
  • Flies act as vectors, in which the bacteria can survive 72 hours
  • Other species non-pathogenic


Characteristics

  • Short, plump Gram negative rods or cocci occuring in pairs
  • Non-motile
  • Aerobic
  • Catalase positive, oxidase postitive
  • Unable to utilise sugars
  • No growth on MacConkey agar
  • Growth enhanced by addition of blood or serum to media


Pathogenesis and pathogenicity

  • Virulent strains have fimbriae, are haemolytic and grow into agar
  • Fimbriae allow adherence to the cornea
  • Q fimbriae are specific for colonisation; I fimbriae allow local persistence of infection
  • Fimbrial antigens stimulate immunity
  • Haemolysin, fibrinolysin, phosphatase, hyaluronidase and aminopeptidase as well as LPS contribute to virulence
  • Haemolysin damages neutrophil membranes; release of hydrolytic enzymes from these neutrophils damages the corneal surface
  • Isolates from carrier animals often avirulent, and are non-haemolytic and have no fimbriae; reversion to virulence can occur


Clnical infections

  • Infectious bovine keratoconjunctivitis, or pink-eye/New Forest disease is an ocular disease of cattle
  • Highly contagious infection of superficial tissues of eye
  • Affects animals under 2 years old
  • Decreased weight gain in beef cattle, decreased milk production in dairy herds
  • Age-related immunity due to previous exposure
  • Antibodies against haemolysin neutralise different strains, whereas antibodies to fimbriae are strain-specific
  • Asymptomatic carrier animals harbour the bacteria in the nasolacrimal ducts, nasopharynx and vagina
  • Transmission by direct contact, aerosol and via flies
  • Clinical signs: blepharospasm, conjunctivitis, lacrimation
  • Keratitis and corneal ulceration, opacity and abscessation may lead to panophthalmitis and permanent blindness
  • Stromal oedema; coning of cornea
  • Cornea may heal or undergo permanent scarring


Diagnosis

  • Swabs of lacrimal secretions
  • Fluorescent antibody test demonstrate presence of M. bovis
  • Culture on blood agar; colonies are round, small, shiny and friable
  • Virulent strains surrounded by complete haemolysis and are embedded in the agar
  • No growth on MacConkey
  • Autoagglutination in saline
  • Short Gram negative rods on smears
  • 7 serotypes based on fimbriae


Treatment and control

  • Subconjunctival or topical antimicrobials
  • Isolate animals
  • Reduce mechanical irritation such as dust, grass, grass seeds
  • Insect control
  • Control concurrent infections
  • Prophylactic oxytetracycline for animals at risk
  • Vitamin A supplementation