About a month ago, Tina thought she noticed her French lop rabbit stumbling. He did it only occasionally, so she put it out of her mind.

A week ago, the 3-year-old rabbit had his head tilted to the right. He seemed normal otherwise, and was eating and drinking and keeping the cats and dog in their places as always. A few days later, Froto began to stumble again and now appears quite weak in his rear limbs.

Froto's symptoms involve a part of the nervous system that produces proper balance and position. It's called the vestibular system and is found to one degree or another in virtually all animals and humans. The head tilt signals a possible neurological problem.

Froto needs a physical examination and blood work to rule out possible metabolic involvement. A thorough evaluation of Froto's ears will help rule out an ear problem as a cause.

I would take radiographs if I suspected musculoskeletal involvement based on physical examination. If my suspicion were correct, Froto's radiographs would be normal. His blood work may be normal or may show evidence of inflammation and a possible issue with his kidneys.

This scenario occurs in many rabbits infected with Encephalitozoon cuniculi. E. cuniculi is a protozoal parasite of rabbits and other animals and humans. It can infect rabbits and cause varying degrees of illness. Some infected rabbits can appear healthy and exhibit no symptoms. These rabbits are called carriers and can pass the disease to other rabbits.

One of the hallmark symptoms for this disease in rabbits is a head tilt, but not all rabbits with this parasite will exhibit head tilts. Other symptoms include weakness, circling when trying to walk and abnormal eye movements. The parasite can involve multiple organs in the body, including the kidneys. Rabbits with affected kidneys will show increased water intake and increased urination and abnormalities in blood work.

Definitive diagnosis of E. cuniculi can be difficult in a living patient, as it involves demonstration of the offending organism in tissue from the patient. Blood testing called serology that can test for exposure to the parasite but a positive result does not by itself prove the bunny has the disease. We can repeat the serology testing a few weeks apart and look for a rise in the immune system response to the organism. If that is found, the likelihood of infection with E. cuniculi is high.

Treatment is available, and I have had the most success using a family of drugs called the bendazoles. These are given orally for four to eight weeks and can effectively clear symptoms. The serology testing done after treatment will still show positive as the body contains antibodies against the organism.

This is a contagious disease often passed from rabbit to rabbit as it is shed in the urine, and the E. cuniculi organism can infect humans, especially young children and adults with immune system compromise. That would include people with HIV and those receiving chemotherapy.