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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