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Encephalitis and Meningoencephalitis in Rabbits

Encephalitis is a diseased condition characterized by inflammation of the brain. It may be accompanied by spinal cord and/or meningeal involvement. When the meningea is involved, the condition is clinically referred to as meningoencephalitis – which is literally a combination of two known diseased states: meningitis - inflammation of the meninges, the protective membrane that covers the brain and spinal cord; and encephalitis – sudden and severe (acute) inflammation of the brain.

Inflammation is usually caused by an infectious agent, viral or bacterial, or by the patient's own immune system. Bacteria may spread to the brain through the bloodstream, through the ears, or through other body systems. The nervous system is primarily involved, but other organs may be involved as well.

This condition is fairly common in rabbits. Lop-eared rabbits may be more likely to show signs of otitis (ear infection) with subsequent meningeal/brain involvement. Dwarf breeds are at increased risk, along with older rabbits, and immunosuppressed (low immunity) rabbits.

Symptoms and Types

• Onset is generally sudden and severe, but there may be a gradual onset with progression to full blown disease
• Signs of respiratory infection, dental disease, and otitis externa/interna before the brain infection sets in
• Thick, white, creamy exudate (fluid discharge) may be found in the horizontal and/or vertical canals of the ears
• Bulging ear drum may be visible
• Neurological symptoms include signs of dizziness and loss of balance
• Based on the portion of the brain most affected
• Forebrain - seizures, personality change, decreasing level of responsiveness
• Brainstem - depression, head tilt, rolling, abnormal rolling of eye balls , facial muscle paralysis, poor coordination

Causes

• Bacterial infection
• Viral infection
• Inflammatory, immune-mediated
• Parasite migration – sporadic cases of Baylisascaris infection (raccoon roundworm)

Diagnosis

Your veterinarian will perform a thorough physical exam on your rabbit, taking into account the background history of symptoms and possible incidents that might have led to this condition, such as recent illnesses, ear infections, or the environment in which your rabbit grazes, if it is allowed to graze outdoors. A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, and a urinalysis. This can be a challenging disease to diagnose, as blood tests often return normal, and visual diagnostics (e.g., X-ray, computed tomography scan) often do not show a significant change in the structure of the brain unless the swelling is considerable.

Because there are several possible causes for this condition, your veterinarian may use differential diagnosis to determine the cause. This process is guided by deeper inspection of the apparent outward symptoms, ruling out each of the more common causes until the correct disorder is settled upon and can be treated appropriately. Skull and ear bone X-rays may identify if a tumor is present. If your rabbit is showing the apparent signs of encephalitis or meningoencephalitis, your veterinarian may be able to diagnose it based on the results of an analysis of cerebrospinal fluid, which can show whether a viral or bacterial agent is present in the fluid.