Moraxella bovis

BACTERIA

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