Roundworms or nematodes makeup the phylum Nematoda which has a tubular digestive system as well as an opening on both ends (the mouth and tail) unlike the flatworms such as tapeworms.
There are many species of nematodes with some being parasitic to plants and animals while others are not parasitic.
For instance, some of the common ones that affect human beings include ascariasis, hookworms, pinworms, trichinosis, whipworms, and strongyloidiasis. However, those that affect rabbits are slightly different, but some may also affect humans, i.e., they may be zoonotic.
Nematodes are common “in lagomorphs with a decreased immune resistance. The population of worms varies according to the age and the sex of the host, but also according to the intestinal bacterial flora of the host”  For instance, pinworms are more often in male as opposed to female rabbits.
Common roundworms in rabbits
In rabbits, some of the common parasitic roundworms noted include the following:
This family has the below species that use the rabbit as their intermediary host and will get into their definitive hosts once these definitive hosts eat the carcasses of a rabbit that has them.
- Baylisascaris procyonis larvae or raccoon roundworm  only as an intermediary worm.
- Bayliascaris columnaris – associated with skunks
- Toxocara canis or dog roundworms
Some of the worms that affect this pet that belong to this family include:
- Passalurus ambiguus or pinworms – Commonly found in proximal colon and cecum. They have no intermediary host and they get directly into their hosts via ingestion of anything contaminated with their eggs.
- Dermatoxys veligera – It common in wild lagomorphs found in the US and has a direct life cycle where the lagomorph ingests the Dermatoxys veligera’s eggs passed out through feces.
Rabbits are their definitive hosts while arthropods are their intermediate host, and these include the following:
- Dirofilaria scapiceps
- Dirofilaria uniformis
- Brugia lepori
The below species have almost a similar lifecycle where they lay eggs inside their hosts, they are passed out through feces, hatch to larvae if there are conducive weather conditions (optimal temperature and humidity). Their first and second larval stage feed on soil and fecal bacteria.
The final infective stage is enclosed in an impermeable sheath that protects it until it is ingested by its definitive host before exsheathment occurs inside the GI (stomach, intestines, etc.). Some that affect rabbits include the following:
- Trichostrongylus calcaratus
- Trichostrongylus sp.
- Obeliscoides cuniculi (stomach worms)
- Nematodirus leporus
- Graphidium strigosum
- Strongyloïdes sp.
Trichuris leporis or whipworms
Trichuris leporis or whipworm in rabbits belong to the family Trichuridae. Their lifecycle involves the egg being ingested and hatches in the duodenum before the larvae moving to the cecum where they feed on blood before moving from the cecum and begin laying eggs in the small intestines.
Also known as lungworms in rabbits, they belong to the family Metastrongyloidea. Their adults live in the lungs of lagomorphs where eggs are hatched. The larvae move to the bronchi where they are coughed out and swallowed and passed out through feces.
Their intermediate hosts are the small snails found on land where they develop into infective stage. Should these snails be swallowed, the infective larvae enter back into lagomorphs.
Clinical signs and diagnosis
The expected clinical signs will be influenced by the specific species of roundworms since different species may show slightly different clinical signs.
Things such as the presence of their eggs in feces, some worms being found in rabbit poop or fecal pellets may indicate their presence. However, the presence of live worms in rabbit cages may indicate something else as these could larvae stages of blowflies in case of flystrike, earthworms especially in their soiled littering tray if not replaced and so on.
Those that affect the GI may cause diarrhea, pain (in case of blockage due to their high population), cecal compaction, gas, stasis, and so on if they are in large numbers (both the dead and live ones). Emaciation, extreme weakness, necropsy, among other symptoms may also be noted. Sudden death may occur but in very rare cases.
Diagnosis is often by fecal floatation test but this test is not conclusive even in heavy infestations. The presence of their eggs in fecal matter, as well as live worms, may also be used for diagnosis.
Treatment of roundworms
Intestinal cases may be treated using benzimidazoles such as fenbendazole and thiabendazole. Alternatively, you can use piperazine which is efficient too.
Due to the different types, proper diagnosis by a qualified vet is necessary as well as a prescription of the right medications.
Prevention will revolve around get rid of any intermediary hosts such as arthropods, insects or other organisms as well as getting rid of or controlling transmission from their definitive hosts if rabbits are only intermediary hosts. Some of the measures to consider include:
- Washing fresh greens and vegetables under running water to get rid of their larvae or eggs.
- Preventing cats, dogs, or other rodents from accessing their foraging areas or do not gather forage from areas where these animals can access.
- Use hay feeder racks if you give them hay that they cannot finish and get rid of any soiled one.
- Clean littering boxes and change their bedding regularly as well as any other items inside the hutch or rabbit run. Use hot water, chlorine, and acetic acid while cleaning. Also, vacuum blankets, carpets, etc., regularly.