February 21, 2018

Old Rabbit Paralysis: Part III


Baylisascaris Procyonis

Q. We have been told that our bunny has “old bunny paralysis” and nothing can be done. Is this true? What is this and why does it happen?

To review briefly, there are many causes of weakness in the pet rabbit. We have discussed vertebral spondylosis and trauma in Part I and a parasite called Encephalitozoon cuniculi. in Part II. In Part III we will discuss another important parasitic cause of neurological disease in the rabbit, the raccon roundworm larva Baylisascaris procyonis.

Cause: Baylisascaris procyonis is the scientific name for a roundworm found in the intestines of raccons in North America, Japan and Germany. It is estimated that some populations of racoons have a 68 to 82% infection rate with this parasite. Skunks carry a similar species, Baylisascaris columnaris that can also affect other species of animals. All the things said about the racoon roundworm will also apply to the skunk roundworm.

B. procyonis does not adversely affect the racoons that carry it. The eggs of the parasite are passed by the millions in racoon feces where they can stay in the environment for years withstanding heat and cold. When a species of animal other than a racoon swallows these eggs the microscopic larva hatches out in the intestine and then burrow through the wall of the intestine and begin migrating through the body trying to find a home. The body tries to kill the larva and it moves rapidly to escape attack. The larva seem to have a preference for lodging in the liver, eyes, spinal cord or brain. Occasionally they can be found in other organs. When a larva tries to make a home it causes a great deal of damage as the body tries to either wall it off or kill it. Eventually it dies and is reabsorbed by the body. In very small species such as mice, it might take only one or two larve in the brain to be fatal. If the larva does not cause significant damage in vital organs then the victim will show no signs of disease. Species other than the racoon that are affected with this parasite CANNOT pass it on to anyone else. This is the end of the line for the the larva and it never becomes a mature adult capable of producing eggs.

There are over 50 species of animals that are affected by this parasite including dogs, squirrels, chinchillas, guinea pigs, mice, rats, birds and humans. This parasite is responsible for disease or death in humans, usually children, every year in this country.

Signs: The signs of the disease are similar in all species affected and depend on the amount of damage and the organ(s) affected. Signs can include any combination of the following: sudden lethargy, loss of balance, abdominal pain, paralysis of one or both sides of the body, loss of muscle coordination, head tilt, blindness, coma and death. In humans the signs appear approximately 2 to 4 weeks after exposure.

Diagnosis: In humans there are more options open for diagnosis of this disease. There is a blood test to find out if the person has antibodies to the parasite. This is currently not available for rabbits. In humans there is a change in the blood count resulting in a high level of white blood cells called eosinophils. These blood cell also occurs in high numbers in the cerebrospinal fluid (the fluid around the brain and spinal cord). Unfortunately rabbits do not seem to respond consistently in the same way. Finally humans can more easily have dye studies done of the brain or other tissues through the use of CAT scans or MRI’s, something that is cost prohibitive or simply not available for the pet rabbit.

Diagnosis in the rabbit is most often based on the rule-out of other disease such as infectious, trauma or E. cuniculi and the possibility of exposure to material contaminated by racoon feces. Unfortunately the diagnosis is often not made until after death when the brain and other organs can be examined microscopically for the presence of B. procyonis larva.

Treatment: Currently there is no effective treatment for this disease. The problem is that there is a great deal of damage already present by the time the rabbit shows signs of illness. Most antiparasitic drugs either cannot get into the tissue in high enough doses once the parasite is being walled off. Some sources suggest that using an antiparasitic drug anyway might slow down or kill the larva that are still migrating, but this has not been proven. The best thing to do is to use high levels of corticosteroids to try to suppress the inflammation that is taking place in the affected tissues. In humans this seems to help alleviate some of the signs as least temporarily. Corticoteroids will not cure the disease nor reverse all the damage, but it may minimize the trauma to the tissue. Corticosteroids have to used with caution in rabbits because they may worsen any bacterial disease present and they may cause alterations in the flora of the cecum.. An injection of a short-acting corticosteroid might be helpful initally and then continued based on the rabbits clinical response.

Prevention: This is really the best option for controlling this disease. Since this disease is just as dangerous to humans and other pets as it is to rabbits then these precautions are doubly important. Here are some recommendation from Kevin Kazacos, DVM, PhD at Purdue University in W. Lafayette, Indiana. Dr. Kazacos is currently doing extensive work studying this parasite in pets and wild animals and has written a number of excellent articles on the subject.

Do not keep racoons as pets. Not only are they not suitable for pets because they are wild animals, but they may pose a serious health risk.
Learn to recognize racoon latrine areas and either stay away from them or clean them up if necessary. Favorite spots are at the base of trees, in the forks of trees, on fallen logs, large rocks, woodpiles, decks, in attics, garages, chimneys, barns and outbuildings. In addtion raccoons like to nest in hay lofts and may contaminate hay or straw that is used for bedding or food. Purchase hay or straw from a clean source and dispose of any bales that show evidence of fecal contamination. Do not store the hay you buy in areas that raccoons have access to. Be cautious using and handling fallen timber for firewood.
Monitor children closely in potentially contaminated areas. Children are the most easily affected because they frequently put unwashed hands in their mouths. Do not house rabbits on the ground in areas inhabited by raccoons. It may be possible to have soil samples tested in your yard to see if the area is contaminated.

Cleaning up a latrine area can be a challenge. The eggs of the Baylisascaris species are extremely resistant to environmental conditions.

The eggs can survive for YEARS. They are resistant to all common disinfectants including bleach. The best way to kill the eggs is through flaming the area (including soil) or burning affected material such as straw or wood cages. Alternately, boiling water can be poured over small areas at a time. In heavily contaminated areas it may be necessary to remove and bury the soil in a deep spot elsewhere. When cleaning up any latrine area, proper protection is a must which should include a dusk mask over the nose and mouth, disposable clothing, disposable gloves and heavy rubber boots that can be cleaned with boiling water.

Prevent further contamination of the area by blocking off access routes for raccoons, not feeding raccoons around the property and using repellents such as mothballs around potential access areas.

In Part IV (the final chapter) of this series we will discuss strokes, infections and systemic disease as well as updates on new findings on the subjects we have already discussed.

Continue To Part IV