Otitis refers to inflammation of one or more structure of the ear and includes otitis externa (the ear canal), otitis media (the tympanic membrane, bony acoustic duct and tympanic cavity), and otitis interna (the inner ear).
A. Otitis externa
Otitis externa is an acute or chronic inflammatory condition of the external ear, and will show some or all of the following clinical signs;
- Scratching – this is most obvious at the base of the ear.
- Head shaking – the movements can be slow or rapid.
- Flopped ears – this will often be asymmetrical if the problem is confined to one ear.
- Pain – some rabbits will just sit quietly with their ears held flat against the head, whilst others may grind their teeth.
- Anorexia – any rabbit that stops eating needs investigating as gut stasis is a serious complication.
- Swelling – look for a distortion at the base of the vertical canal. This is caused by inflammation and degeneration of the canal tissues.
- Discharge – check for purulent material in the vertical canal.
- Lethargy – most rabbits will become quite unsettled and depressed. Owners may notice they no longer play or explore their environment.
- Normal neurological examination – this is helpful to differentiate between the different variations of otitis. You’ll need to assess the function of cranial nerves VII, VIII and IX, which should be normal.
With any suspected case of otitis, the ear needs to be examined carefully. It’s often necessary to clean and remove all wax to allow a clear view of the tympanum and canal.
Whilst primary bacterial infections are rare, secondary infections are more likely. If you suspect otitis externa, take a swab to culture and check antibiotic sensitivity. Cytology can be used to confirm if there are large numbers of white cells or bacteria. Be aware that since rabbit ear wax is thick and appears similar to pus, you may suspect an infection yet find nothing. Parasitic problems are also common, so check under the microscope for Psoroptes cuniculi.
Have you read our article on Psoroptes in rabbits?
Cleaning with ear cleaning fluids should only be performed if the ear drum is intact, so always check first.
Non-steroidal anti-inflammatory drugs (NSAID’s) such as meloxicam and carprofen, can be used safely, either topically or systemically.
The choice of antibiotic needs to be considered carefully, as rabbits are particularly at risk of developing antibiotic induced bacterial overgrowth.
B. Otitis media
Otitis media refers to a condition which results in inflammation of the middle ear. It often goes undiagnosed in the early stages as the clinical signs can be hard to spot. As a result of this it is often only diagnosed from X-rays, CT or MRI.
Some of the signs may be similar to otitis externa, so look out for;
- Pain – especially when the head and ear base are touched.
- Lethargy – the rabbit may hide away or sit all day in one location.
- Inappetence – as less food is eaten, fewer faecal pellets will be produced, so make sure you check faecal output.
- Head wobble – there may also be a very subtle head tilt.
- Swelling at the base of the ear – this swelling might not be visible through the hair but will be more obvious when palpated.
- Facial paralysis – this is usually on the side of the lesion.
Diagnosing otitis media
- CT – this is the most reliable method and will allow you to identify accumulations of fluid or pus within the tympanic bulla.
- Radiography – this tends to be a poor diagnostic technique, however in most general practice situations, it’s often all we have available. The dorsoventral view is most useful, with lateral and oblique views are also taken. Look for increased sclerosis of the bone or radio-opacity of the bulla.
- Positive contrast canalography – this may be useful, especially if contrast fluids pass into the bulla and confirm a ruptured tympanic membrane.
What are the causes?
As many as 1 in 3 rabbits with respiratory pasteurellosis will suffer from otitis media, so if signs of ear disease are found, the rabbit needs to be checked for underlying respiratory disease as well. It’s possible for a rabbit to have a positive bacterial culture from the bulla but be negative on nasal swabs. Cases with clinical signs of upper respiratory tract disease or Pasteurella multocida are likely to be caused by ascending infections via the eustachian tubes.
Other pathogens which can cause the infection include;
- Bordetella bronchiseptica
- Staphylococcus spp.
- Escherichia coli
- Pseudomonas aeruginosa
C. Otitis interna
This condition will eventually develop if otitis media remains undiagnosed and untreated. It usually presents at the same time as otitis externa, and is the result of inflammation, infection and increased pressure. Signs to look for include;
- Head tilt – the tilt will be on the side of the affected ear.
- Nystagmus – this can be induced by postural changes, with the eye movements being horizontal.
- Ataxia and circling – animals are usually markedly uncoordinated. Any inflammation or infection in the inner ear will cause a vestibular neuritis and loss of balance. Some rabbits may even start flipping, with uncontrolled rotational movements of the whole body.
- Facial paresis - the facial nerve exits ventral to the vestibulocochlear nerve in the internal acoustic meatus, so when affected, will cause the facial muscles to respond abnormally. The facial nerve (VII) relays sensory information from, and motor activity to, the mandible, maxilla and eyelids. In such cases, the animal may find it difficult to open its mouth, blink, and twitch its nose. Drooping is most evident on the upper eyelid and ear.
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