Ear infections, or otitis media/externa, is most commonly the result of bacterial colonization of the inner or middle ear. Affected calves show cranial nerve deficits such as a head tilt and facial nerve paralysis, but may progress to meningitis and seizures. Otitis is also commonly associated with pneumonia.
Ear infections in calves are commonly the result of bacterial infections. One of the most common bacteria responsible is Mycoplasma bovis, however other bacteria include Listeria monocytogenes, Haemophilus somnus, Streptococcus spp., Arcanobacterium pyogenes, Mannheimia haemolytica, and Pasteurella multocida. Ear mites (Raillietia auris, Psoroptes cuniculi, and Rhabditis bovis) can also be the causative factor.
Three modes of spread can result in transmission to the inner ear. In the case of Mycoplasma bovis, the consumption of unpasteurized waste milk contaminated with the bacteria results in hematogenous spread through the blood stream, and colonization of the bacteria within the inner ear. Secondly, bacteria present in the nasopharynx may travel up the Eustachian tube to the ear canal. Lastly, bacteria may spread from an otitis externa, or infection of the outer ear, and travel down the ear canal to the inner ear.
Due to the fact that the inner ear is closely associated with Cranial Nerves VII(facial) and VIII(vestibular), presenting signs of inflammation to this area are the result of insult to these nerves. The first sign of an ear infection affected the vestibular nerve (inner ear) is generally a head tilt towards the infected ear, whereas inflammation of the facial nerve (middle ear) will result in paralysis of the affected side of the face including an ear droop, weakness of the eyelid, and drooping of the facial muscles. Paralysis of the eyelid and the failure to protect the eye can result in complications such a keratoconjunctivitis sicca (dry eye) and corneal ulcers. Irritation to the eye can result in excess tearing, or epiphora. Severe inflammation of vestibular nerve can result in nystagmus and circling towards the side of the lesion (e.g. lesion in the right ear causes circling to the right). In the initial stages of disease, cranial nerve deficits may be the only appreciable sign, however as the disease progresses the animal may become febrile and anorexic. Otitis is also commonly associated with the development of pneumonia, and severe cases may result in meningitis and progression to seizures.
In the case of mycoplasma otitis, the most effect method of prevention is to pasteurize waste milk that is fed to calves to kill the inciting bacteria. Vaccinations for M. bovis are available, however results in successful prevention of infection have been highly variable.
The most effective treatment of otitis is antibiotic therapy to treat the underlying bacterial infection, however gross examination of the ear should be completed before pursuing treatment, as the observation of mites would dictate a parasiticide treatment (ivermectin) in conjunction with an antibiotic. Drugs that are known to be effective against mycoplasma and are capable of penetrating into the ear include tetracycline, spectinomycin, tylosin, and fluroquinolones. Note that enrofloxaxin (Baytril) has been successful in treating otitis, however this drug is only FDA approved for use in respiratory disease. Effective treatment regimens range from 5 days to 2-3 weeks, and success is highly variable depending on the length of the infection and the pathogen involved. Flushing of the ear canal with dilute iodine or chlorhexadine is also recommended, particularly if the tympanic membrane has been ruptured. Treatment with anti-inflammatories such as flunixin meglumine may be beneficial in resolving the cranial nerve symptoms.
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