Pinworms or oxyurids are the most common roundworms or nematodes that affect rabbits and hares with Passalurus ambiguus or Oxyuris ambigua species being the most common one. However, this species does not affect other animals or human beings.
The P. nonanulatus has been noted in various places including the United States, some parts of Europe among other places, i.e., they have been reported in lagomorphs globally and they have been commonly reported in laboratory rabbits.
In terms of their appearance, these parasites are glistening white in color, about 10mm in length with the males being shorter in length when compared to females, i.e., about 5mm while females can be about 10mm in size.
One interesting fact about these worms is that “the female worms emerging from the anus of rabbits contain eggs in the gastrula stage that are able to develop into an infective stage in the environment” 
Lifecycle and transmission of Passalurus ambiguus
They have a direct lifecycle with no intermediary host. Adult ones are found in cecum anterior area and in colons while young ones are common in the small intestines and cecal mucosa. Furthermore, the adult’s pinworms lay eggs that are shed into feces and later passed out together with feces.
Therefore, transmission is by ingestion of food or water contaminated with feces from infected rabbits and it can occur even at the breeder’s place, from parents to kits especially during cecotrophy, or at pet stores.
Some rabbits can host many of these parasites without showing any symptoms since they are non-pathogenic, and they cause little or no harm. Some people may notice them incidentally during examination especially after death caused by something else and not these parasites.
At times, dult pinworms may be passed out in fecal pellets and they may be found on freshly passed poop and this might be an indication of infestation. However, they may dry up with a short time and they are usually passed out together with pop when they grow old.
Also, you may notice thread like mucus in droppings which may indicate infestation. However, you should not confuse this with mucoid enteritis.
Overpopulation of pinworms may cause GI stasis, gas, cecal impaction as well as severe pain and the GI stasis may be chronic if they are not treated within a month or a month and a half.
Also, “pinworms may cause moderate to severe itching, skin inflammation, and redness, especially in the genital and anal area”  and in a very rare occasion, they may be associated with weight loss, poor fur coat quality, and rectal prolapse.
Finally, poor procreative performance has also been associated with a severe infestation as well as poor weight gain, bloody feces, among other symptoms.
Diagnosis is by fecal floatation test but rabbits that are heavily infested might bring a negative result making this means of diagnosis not conclusive.
Microscopic smear or centrifuge technique may also be used to detect the presence of their eggs in fecal pellets.
Also, a differential diagnosis might be necessary including urinalysis and blood samples taken to be certain the cause of some of the symptoms is indeed the pinworms.
Finally, your vet may notice the visible worms themselves especially around fresh stool as already mentioned.
Treating pinworms in rabbits
Treatment is by piperazines such as piperazine adipate (200 mg/kg dose and another one after 14 days), or by benzimidazoles such as fenbendazole (20mg/kg, and repeated after 14days), mebendazole ( 20-50mg/kg single dose), thiabendazole (100-200mg one treatment) and oxibendazole (15mg/kg and repeated after 14 days) all given orally.
Usually, to avoid reinfection, your vet may recommend treating these pets again after some time as well as putting in place various prevention measure to stop reinfection.
Unfortunately, although helpful, cecotrophy may further complicate treatment as these pets will be ingesting their cecotrophs and this can be a source of contamination.
Prevention of ringworms in rabbits will involve several things that include:
- Get fresh stock from breeders who are certain their rabbits are free from these worms.
- Thoroughly sterilizing and cleaning areas where infested bunnies lived before allowing any new bunnies to live in such areas and isolate the infected ones to avoid the spread of non-infected bunnies.