Parasitic worms of the digestive tract

Generalities

Esther van Praag, Ph.D.

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Warning: this file contains pictures that may be distressing for some persons.

The digestive tracts of rabbits, hares, and cottontails can be home to dozens of different parasites. Some are very rare, some are pathogenic only under exceptional circumstances, and others have barely been studied. In this article, we will be discussing the most commonly found parasitic worms of house rabbits.

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Worm infestation is possible after ingestion of contaminated hay

Wild rabbits, as well as healthy house and pet rabbits living in clean conditions, can be infested by gastrointestinal parasites. In the case of pet rabbits, the life cycle of the parasites is often disrupted when the appropriate conditions for the development of the larval stages (L1, L2, and sometimes L3) are not met indoors.

Many parasites are heteroxenous (multihost), meaning they must complete intermediary stages in several hosts before reaching the final host for reproduction. For instance, the different juvenile forms of the liver fluke (Fasciola hepatica) are found in certain snails in the grass of marshy areas before entering the rabbit digestive tract. The little fluke larvae (Dicrocoelium lanceolatum) must live in snails and ants before becoming infective in rabbits. Such parasites are rarely found in indoor-dwelling rabbits due to the disruption of their life cycle caused by the absence of intermediate hosts in the home environment. Other parasites are monoxenous, meaning they live and reproduce on a single host. Their larval stages are typically found in wet grassland, stagnant water, or hay before being ingested by the unique and final host, the rabbit. Such worms are more frequently observed in domestic rabbits.

In order to prevent worm invasion in a house rabbit, it is essential that:

· Forage should not be gathered in areas where there are numerous dogs, cats, or rodents;

· Fresh greens and vegetables be washed carefully with running water;

· Hay and straw used as litter be changed regularly (this avoids attracting flies too);

· Hay that cannot be changed daily should be provided in feed rack, where it cannot be soiled with feces or urine;

· Litter boxes be cleaned daily, using hot running water, vinegar, or chlorine;

If a worm infestation does occur in a house rabbit, it can be effectively treated with the proper medication. It is essential to consult a veterinarian prior to treatment to determine the type of worms present. It is essential that the prescribed timing for the medication be strictly adhered to.

Nematode parasitic worms

The term "nematode" is derived from the Greek words "nematos" (thread) and "eidos" (form), which refer to their filariform shape. Nematode worms are among the most abundant multicellular animals on Earth.

An adult worm consists of approximately one thousand cells, of which a hundred are involved in reproduction. Other cells have specialized digestive, nervous, or excretory functions. These parasitic worms are devoid of both circulatory and respiratory systems. Their structure is simple, consisting basically of "a tube within a tube," with an alimentary canal extending from the poorly developed buccal part to the posterior anus. Parasitic nematodes (pinworms and oxyurid) are commensal, little- or non-pathogenic, bacteria-feeding roundworms that generally inhabit the lower portion of the intestine. Although they are prevalent among vertebrate hosts, they typically exhibit host specificity, infecting primarily cattle and rabbits. However, there have been documented cases of cross-transmission.

Nematodes are more prevalent in lagomorphs with compromised immune systems. The population of worms is subject to variation based on factors such as the age and sex of the host, as well as the intestinal bacterial flora of the host. Male rabbits are more susceptible to infestations of pinworms than females. A high-fiber diet has been shown to reduce the population of worms. Pinworms are a cosmopolitan, with some species exhibiting higher prevalence in certain regions. The population of worms fluctuates according to its life cycle in the host.

Samuel Boucher and Loïc Nouaille Cecum and intestine of a healthy rabbit, devoid of parasitic nematode parasites

Samuel Boucher and Loïc Nouaille Damaged cecum of a rabbit with a severe infestation of Passalurus sp.

At this stage, the worms will be shed and can be observed in the dropping of the rabbit. In certain instances, an overpopulation of parasitic worms in the intestine can result in intestinal stasis and severe discomfort and pain.

Simone van der Meij Fresh droppings with hair (fine white filament) and worms (thick translucent threads)

Simone van der Meij Fresh dropping with hay fiber (short yellowish stalks) and live roundworm

After being expelled, the surviving worms begin a new cycle of growth in the cecum. During this cycle, the worms shed eggs that may be reingested and reinfect the rabbit.

Nematode parasitic worms of the domestic rabbit

Parasitic nematodes most frequently found in the gastrointestinal system of rabbits are:

Oxyuridae	Passalurus ambiguus
	Dermatoxys veligera
.
Trichostrongylidae	Trichostrongylus calcaratus Trichostrongylus sp.
	Obeliscoides cuniculi
	Nematodirus leporus
	Graphidium strigosum
	Strongyloïdes sp.
.
Trichuridae	Trichuris leporis
.
Filarioidideae	Dirofilaria scapiceps
	Dirofilaria uniformis
	Brugia lepori
.
Metastrongyloidea	Protostrongylus boughtoni
.
Ascaroidea	Bayliascaris procyonis
	Bayliascaris columnaris
	Toxocara canis

Clinical features and diagnosis

The presence of threads of brown mucus in the droppings may indicate the presence of intestinal worms. When reaching a peak number, they can cause pain, and the mass of live and dead adult worms may lead to cecal impaction, accompanied by stasis, severe pain, and gas formation. This is not related to the type of worm present in rabbits, whether it is a pinworm or a tapeworm.

www.powhatananimalhospital.com/disease/roundworminfect.jpg

Small intestine infested by roundworms

In rare instances, sudden death may occur in the absence of prior clinical symptoms of disease or indications of parasitic worms detected during previous fecal flotation tests. During the necropsy, the cecum was found to be heavily infected with pinworms. The site of the worms' location showed signs of inflammation and presented dystrophic modifications.

The presence of intestinal parasites is determined by a fecal flotation test. In rare cases, the fecal flotation test result of heavily infested rabbits can return negative. If left untreated, the presence of worms will be observed in the droppings.

Treatment

The presence of parasitic intestinal nematodes must be treated with benzimidazoles, specifically fenbendazole or thiabendazole. Piperazine has proven effective, while ivermectin has been observed to be ineffective against certain roundworm species (e.g., Passalurus sp.). Praziquantel is the recommended treatment for tapeworm infestations in rabbits.

For more in-depth information and treatment options, please refer to the texts related to the particular worms.

Acknowledgement

Thanks are due to thank Simone van der Meij, and her rabbit Jasper, for the pictures or worm-infested droppings, and to Arie van Praag, for the picture of Flora.

Further information

1. G. M. Urquhart, J. Armour, J. L. Duncan, F. W. Jennings, A. M. Dunn (1996) Veterinary Parasitology, Blackwell Science Inc; p. 307.

2. J.E. Harkness, J.E. Wagner (1995) The Biology and Medicine of Rabbits and Rodents, Williams and Wilkins. p. 372.

3. S. Boucher, L. Nouaille (2002) Maladies des Lapins. Editions France Agricole, p. 122-135

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