Morxella

• Case concerns a herd of 350 Herefords on range during dry, dusty weather.
• There was bright sunlight the past several weeks with tall grass and numerous flies.
• Infections occurred in 165 animals, but most (110) were less than 2 years old.
• Initial symptoms of infections include photophobia and excessive lacrimation, and mucopurulent discharge from the eye.
• Animals develop conjunctivitis and keratitis, and seek shade.
• Mild fever develops in some animals, and some have depressed appetite and milk production.
• Some infections persist for days to weeks and are bi- and uni-lateral.
• Serology is the most common method of diagnosing Novidica.
• FA and PCR are also methods of diagnosing Novidica.
• Novidica is a notifiable disease.
• Novidica, which grows on blood agar, takes 2-4 days to grow.
• Streptomycin or other aminoglycoside and tetracycline are synergistic and the combination is the treatment of choice for Novidica.
• Novidica requires a BSL-3 lab to isolate, but the isolate must then be destroyed.
• Ciprofloxacin and some cephalosporins can be used in humans for the treatment and prophylaxis of Novidica.
• Avoid rabbits, especially in Martha’s Vineyard, as they are susceptible to Novidica.
• Conjunctivitis and ulcerative keratitis can be severe, with occasional penetration of the anterior chamber.
• Opacities involving the entire cornea occur in some cases.
• Moraxella bovis appear as Gram-negative diplococci and are not true coccus, cells are rod-shape around penicillin disk.
• Moraxella bovis are strict aerobes and nonsaccharolytic, they oxidize organic sulfur and nitrogen (e.g. amino acids).
• Moraxella bovis cause infectious bovine keratoconjunctivitis (IBK) (bovine pinkeye).
• Predisposing factors for IBK include sunlight (UV light), breed (non-“hooded” eyelids), flies (also involved in transmission), irritation (dust, grass), and prior infection.
• Animals less than 2 years old are most susceptible to IBK due to lower immunity.
• Transmission of IBK occurs through direct contact with fomites.
• Cattle with “hooded” eyelids are most resistant to IBK.
• Pili (fimbriae), required for adherence to cells and cytotoxic, come in two types (Q and I) and enhance corneal pitting.
• Vaccination requires about 4 weeks to get protective antibodies.
• Pannus formation, where the cornea becomes white and irregular, can occur due to chronic inflammation.
• Chronic inflammation can cause increased pressure in the eye.
• Hemolysin, a cytotoxin required for virulence, enhances lesion formation.
• Live vaccine is best, but only bacterins are available.
• Subunit vaccines have shown some promise, but may be too specific.
• Prevention involves animal management and fly control.
• The most virulent strains of Moraxella bovis are known to be hemolytic and highly piliated.
• Vaccination is useful only in herd outbreaks and uses a strain isolated from the herd so pili are antigenically identical.
• Immunity involves antibodies to pili being protective, but strain-specific, and IgA antibodies being highest in lacrimal secretions but may not prevent clinical disease.
• Secondary infection of the eye, known as endophthalmitis, occurs with pus in the anterior chamber.
• Cell detachment factor is a cytotoxin/hemolysin and enhances corneal pitting.
• Capsule, a role in disease unknown but probably a bacterial protective function, is a virulence factor.
• Cytotoxin/hemolysin (RTX toxin), a cytotoxin/hemolysin, is a cytotoxin/hemolysin and enhances corneal pitting.
• Pathogenesis involves bacteria adhering to corneal epithelial cells, toxins causing “pits” or depressions in cornea, and PMNs infiltrating the lesion and causing inflammation.