Intestinal Parasites: The Hitchhikers Inside Your Bunnyby Astrid M. Kruse, DVM
All animals have some number of bacteria, worms and assorted bugs living inside their gastrointestinal tract. Most of the time, these hitchhikers cause no problems. After all, they have been flourishing inside their intestinal homes for millions of years, and don't want to kill their hosts, just live off them. However, when parasite numbers reach a critical level, they can cause illness. Coccidia (Eimeria species) are the most common parasites in rabbits, causing weight loss, diarrhea and dehydration, affecting younger rabbits the worst.
Coccidia are little, round manycelled organisms that infect the bunny when they are eaten. They hatch out of their shells once inside the intestines. One species of coccidia (Eimeria stiedae) will then travel to the liver and cause liver and bile duct damage, while the others invade and damage the cells of the intestines. Their offspring are shed in the rabbit's feces, and after 48 hours in the environment, are able to infect the next rabbit that eats them. (Cecotrophs, aka cecal pellets, are eaten fresh and thus aren't infective.) Coccidia can live for years in an untreated environment because they have protective capsules or cysts, but they can be killed by thorough cleaning and drying. They are mainly a problem in dirty, overcrowded living conditions, which occur at some breeding establishments and farms.
Your vet will be able to tell if your bunny is infected by analyzing a fresh fecal sample. This sample can be looked at in the clinic, but the most reliable test for finding fecal parasites in any species is by zinc sulfate centrifugation, which is done at a regional lab. However, even if there are coccidia in a sample, they may not necessarily be the cause of the intestinal problem, since most rabbits are infected without becoming sick. All parasites shed eggs in the host's feces only intermittently, so while one sample may show no parasites, the next very well might. Technically, there must be seven fecal samples collected at different times that are negative (meaning no eggs are seen) before we can be sure that the parasites are really all gone. Coccidiosis is treated with sulfa-based drugs, usually Albon or Bactrim, for at least a week. Remember that the treated bunny can be re-infected if the living environment is not thoroughly decontaminated by cleaning and drying. Eventually, a rabbit will develop immunity.
Tapeworms and flukes rarely cause problems. They infect rabbits that eat fresh grass that has on it either mites or ants (for tapeworms) or snails (for flukes). The stomach worm Obeliscoides cuniculi can, with a heavy infection, cause weight loss and a decreased appetite. If you are keeping your bunny indoors and feeding hay from a reputable source, he or she will be safe. The rabbit pinworm Passalurus abiguus can sometimes be seen in the fresh feces (apx. 3/16-inch long, whitish).
While observing wriggling worms in your bunny's poop might be disturbing, these actually do not cause a problem for the rabbit, and are treated more for aesthetic reasons. All of these parasites are easily treated with deworming medications. Luckily, even if a human were unfortunate enough to be eating bunny poop full of parasite eggs, none of these parasites can infect humans. However, pets like dogs and cats often carry parasites that cause blindness in children, skin problems, and potential birth defects, as well as illness in rabbits and other pets. For public health reasons and the safety of your rabbit, dogs and cats need to be dewormed and have their stool checked regularly. Ideally, cats should not be allowed to hunt outside.
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