Moraxella infections

STEPHANIE SPECK

B undeswehr Institute of Microbiology, Department of Virol­ogy and Rickettsiology, Munich, Germany

There are 10 species within the genus Moraxella. Moraxella bovis (synonym: Haemophilus bovis) is the agent of infec­tious bovine keratoconjunctivitis (IBK), and M.

Moraxella organisms are non-motile Gram-negative rods (1.0-1.5 ? 1.5-2.5 μm), which appear characteristi­cally in pairs but may also be seen in short chains. Morax- ella are strictly aerobic, asaccharolytic, oxidase-positive and usually catalase-positive. They are susceptible to desicca­tion and do not survive long outside the animal host.

IBK, also named ‘pink eye’ or ‘New Forest disease’, is a highly contagious ocular disease of cattle with worldwide distribution. It causes blepharospasm, epiphora, corneal opacity, corneal ulceration and conjunctivitis in domestic and wild ruminants.

In a study on Spanish ibex ( Caprapyrenaica hispanica), M. bovis was isolated from conjunctiva (1.5%) and nasal swab (0.6%) samples from apparently healthy animals. In the same study, M. (Branhamella) ovis was detected in 5.3% of conjunctival swabs and in 1.5% of the nasal samples investigated¹-²⁶). Both agents have been associated with IKC in roe deer (Capreolus capreolus)¹⁶6 and were isolated from clinically healthy bighorn sheep (Ovis canadensis) in the USA. Moraxella bovis was also isolated from a moose with keratitis in Canada⁽⁷⁷⁾, and M. ovi( has been implicated in epizootics of IKC in mule deer (Odo- coileus hemionus) and moose (Alces alces) in the USA⁽⁷⁸⁾.

Moraxella bovis is maintained in the conjunctiva, nasopharynx or possibly vagina of clinically normal cattle older than 2 years. Moraxella ovis is considered a commen­sal of the conjunctiva and upper respiratory tract in sheep, cattle and goats. Virulent M. bovis strains possess pili, and produce a haemolysin and a cytotoxin that damages bovine neutrophils. Lipopolysaccharides, a collagenase and a hyaluronidase may also contribute to virulence. Predispos­ing environmental factors such as irritation of the eye by ultraviolet light, dust, long vegetation and flies are impli­cated in IBK⁽⁷⁹⁾. Pathogenicity of M. ovis is considered low, and the pathogenesis of M. ovis infection remains poorly understood, but haemolytic, non-piliated isolates have been involved in epizootic IKC in free-ranging cervids⁽⁷⁸⁾. Transmission is by direct contact or via insects. The follow­ing eye lesions have been described in M. bovis or M. ovis infections: inflammation of the conjunctiva and cornea, corneal ulceration, oedema surrounding the ulcer, vascu­larization of the cornea, characteristic red cone of granula­tion tissue (in cattle), corneal rupture and anterior synechia, loss of the lens, anterior uveitis and hypopyon^(77-79).

Clinical signs of Moraxella infection include excessive lacrimation, blepharospasm, corneal scars, corneal opacity, keratitis and mucopurulent conjunctivitis.

For diagnosis, swab samples for bacterial culture should be taken deeply from the inner corner of the eye. Inocula­tion on agar plates must be done as soon as possible after collection of samples. If this is not possible, a transport medium to prevent desiccation is recommended. Gram- stained smears are of little practical use, but the fluorescent antibody technique has been used to demonstrate and identify M. bovis. Serological assays are not available⁽⁷⁹⁾.

There are no suitable measures for the control and treat­ment of IBK and IKC in wild animals.