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Companion animal practice
Gastrointestinal disease in rabbits 2. Intestinal diseases
  1. Brigitte Lord

Abstract

Intestinal diseases in rabbits can develop as a result of many causes. Dietrelated problems are a common aetiology of intestinal disorders but infectious (bacterial, viral, parasitic), idiopathic and neoplastic diseases are also seen with relative frequency. This article describes the diagnosis and approach to treatment of intestinal diseases in rabbits. An article in the February issue of In Practice (volume 34, pages 90–96) considered gastric diseases in this species.

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Brigitte Lord graduated from the Royal Veterinary College in 2002. After a period in exotic and small animal practice, she spent time at the Royal (Dick) School of Veterinary Studies in Edinburgh and the University of Bristol/Bristol Zoo, and ran a rabbit and exotics veterinary referral service in south-west England. She returned to Edinburgh in 2008 as a lecturer in rabbit medicine and surgery, and is now head of the university's exotic animal handling facility. She is also the veterinary adviser for the British Rabbit Council. She holds the RCVS certificate in zoological medicine and is currently working towards the diploma in zoological medicine.

Intestinal ileus and obstruction

Caecal stasis is primarily an acquired disorder of decreased motility. Generalised ileus is a common continuation of this condition and may arise from mechanical obstruction or from defective propulsion, as seen with gastric stasis (see Part 1). Obstruction of the small and the large intestine has been reported in rabbits, with the small intestine being more commonly affected (Harcourt-Brown 2007). Foreign bodies were most frequently found in the small intestine and included locust bean seeds from mixed muesli-type rations, carpet fibre and pellets of compressed hair. Post-surgical adhesions, an inguinal hernia and a tapeworm cyst causing strangulating obstructions of both the small and large intestines were seen. Neoplasia was found to cause obstruction in all areas of the gastrointestinal tract.

Rabbits have complex large intestines, which are typical of hindgut fermenter species (Fig 1), in contrast to the simple gastrointestinal tract of cats or dogs.

Fig 1

Normal gastrointestinal tract of a rabbit on postmortem examination. The large caecum (F) is typical of a hindgut fermenter species. A Stomach, B duodenum, C pancreas, D jejunum, E sacculus rotundus, F caecum, G caecal appendix, H proximal colon, I fusus coli, J distal colon, K rectum, L anus

Diagnosis

The history and clinical findings of a firm, dough-like or gas-filled caecum on palpation allow a presumptive diagnosis of caecal stasis and ileus. Non-obstructive and obstructive ileus can usually be differentiated on the basis of the clinical appearance of the rabbit and its response to treatment, although advanced non-obstructive disease may be more challenging to interpret (see Box 1). Non-obstructive ileus can usually be managed medically, while obstructive ileus will require surgical treatment.

Box 1: Diagnosis and management of ileus

Radiography is indicated if obstructive disease is suspected. Dilation of the region proximal to the obstruction is diagnostic for the condition and, in such cases, an emergency laparotomy should be carried out, as described below. Serial radiographs may be useful in some cases to confirm a suspicion of obstruction. In advanced cases of ileus, the stomach often contains ingesta but the large and small intestines are gas-filled (Figs 2, 3).

Fig 2

Dorsoventral abdominal radiograph of a rabbit showing gas distension of the caecum, which has been displaced to the left side of the abdomen

Fig 3

Lateral abdominal radiograph of the same rabbit as pictured in Fig 2, showing the gas-filled caecum. The stomach is full of ingesta, and the small intestine and colon are empty

Treatment and prognosis

Aggressive medical management is required to prevent further deterioration and death in rabbits with intestinal stasis and ileus. The provision of rehydration, analgesia, prokinetics and nutritional support with a high-fibre diet is vital in these cases, as described in Part 1 for gastric stasis and ileus.

If obstructive disease is suspected or diagnosed on radiography, an exploratory laparotomy is indicated. These patients are likely to be critically ill, so care must be taken in the perioperative period. The anaesthesia protocol described in Part 1 for gastrotomy procedures is recommended. A routine laparotomy incision should be made as described for a gastrotomy (see Part 1) and the entire gastrointestinal tract should be explored. The area of affected bowel should be exteriorised (Fig 4) and the abdomen packed off adequately to prevent contamination. An assistant's fingers or atraumatic forceps should be used to prevent ingesta contaminating the surgical field. Ideally, an incision should be made in a healthy portion of intestine, and the foreign body can then be ‘milked’ into the incision. Milking a small intestinal foreign body into the caecum for removal, where possible, may reduce the likelihood of mortality. For firmly attached obstructions, an incision should be made just next to the lesion. If the cause of obstruction is a foreign body, it should be removed or, in the case of a neoplasm, an enterectomy and histopathology of the excised tissue should be considered.

Fig 4

Exploratory laparotomy can be made a lot easier by using a retractor. The large caecum is present just below the abdominal muscle layer, so care must be taken on entering the abdomen to make sure the caecum is not lacerated

If no intestine is removed, the incision can be closed with a simple interrupted suture pattern using syn- thetic absorbable monofilament material (eg, polydioxanone [PDS II; Ethicon]). If the incision was made in the caecum, a second layer of inverting sutures should be placed. It is important to use a small needle to prevent leakage of the caecal contents or tearing through this very thin-walled structure. Omentum can be tacked around the incision site. The abdomen is then closed as described for gastrotomy (see Part 1).

Perioperative mortality can be high in rabbits with intestinal obstructions, but with excellent perioperative care a good outcome can be achieved. The prognosis is grave for rabbits with an obstructing neoplasm, and euthanasia should be considered in such cases.

Parasitic enteritis

Nematodes and cestodes

Passalurus ambiguus, the pinworm, is common in domestic rabbits and widespread in wild rabbits. Embryonated P ambiguus ova are transmitted by the faeco-oral route. Adult worms, which are 2 to 11 mm long, inhabit the caecum and colon, and are often seen when they are passed in fresh faeces. Graphidium stringosum, Trichostrongylus retortaeformis and Trichostrongylus calcaratus are nematodes found commonly in wild rabbits in Europe, and domestic rabbits allowed to graze infected pasture may acquire these infections (Allan and others 1999).

Rabbits are the intermediate host for several tapeworms that affect dogs and foxes, including:

  • The larval stage of Taenia pisiformis (sometimes known as Cysticercus pisiformis);

  • The larval stage of Taenia serialis (sometimes called Coenurus serialis);

  • Echinococcus granulosus.

Transmission of these species is by the ingestion of eggs shed in the faeces of carnivore hosts. The larvae migrate from the intestines to their predilection sites: the liver, lung, lymph nodes, intermuscular connective tissue and, occasionally, the orbit or brain.

Rabbits are one of the primary hosts for Cittotaenia variabilis. Oribatid mites may be the intermediate host of this species.

Generally, P ambiguus is considered to be non-pathogenic, although rabbits with heavy infections may show perianal pruritus. Cestode infections are usually asymptomatic, but abdominal distension, lethargy and weight loss may be seen in cases of heavy infection. T serialis usually forms subcutaneous cysts, which can be palpated as soft tissue swellings (Bethell and Truszkowska 2010). The clinical signs will depend on the site and extent of the space-occupying lesion.

Diagnosis

P ambiguus ova can be observed on faecal flotation or by examination of fresh faecal smears. A definitive diagnosis of tapeworm infection can be made on examination of a tissue biopsy or fluid aspirated from cysts.

Treatment and prognosis

Anthelmintics that can be used to treat nematode or cestode infections in rabbits are listed in Table 1. T serialis cysts should ideally be surgically excised or drained by aspiration. The prognosis for recovery is good, unless the animal is severely affected by the space-occupying lesion or shows severe liver pathology. Prevention of worm infections in rabbits can be achieved by ensuring that they do not have access to grass contaminated with carnivore faeces.

Table 1

Drugs used in the treatment of intestinal disease in rabbits

Cryptosporidiosis

Rabbits become infected with Cryptosporidium parvum when they ingest sporulated oocysts. These are shed in wild or domestic rabbit or rodent faeces, but may also be transmitted in water, fomites or contaminated feed. The prepatent period is three to 21 days. Adult rabbits tend to be subclinically infected and show no clinical signs unless they are immunocompromised. Infected neonatal or young rabbits may show lethargy, poor body condition, poor coat quality, decreased appetite, dehydration, weight loss and pasty, unformed faeces or diarrhoea lasting for three to five days.

Diagnosis

The diagnosis of cryptosporidiosis requires finding the oocysts on faecal examination (see Part 1).

Treatment and prognosis

Currently, there are no treatments known to be reliable for cryptosporidiosis in rabbits. The prognosis for recovery is guarded to good, depending on the severity of infection and the degree of villous blunting in the intestine. Young rabbits with severe stunting may never attain their anticipated body size.

Intestinal coccidiosis

Many different species of Eimeria have been identified in rabbits. Eimeria perforans, Eimeria media and Eimeria magna are widespread in breeding colonies of domestic rabbits, while E perforans is the most common species in wild rabbits. Transmission is via ingestion of sporulated oocysts. The prepatent period for Eimeria species ranges from two to 10 days, and, at a temperature of 20°C, sporulation requires 22 hours for E perforans and 70 hours for Eimeria piriformis.

Intestinal coccidiosis is most often a subclinical disease in immunocompetent adult rabbits. The factors predisposing to clinical disease are:

  • Coinfection with other enteropathogens;

  • Immunosuppression or a naive immune system;

  • The dose of infection present;

  • The species of Eimeria involved. E perforans affects the small intestine and, although it is associated with only slight pathogenicity, is the predominant species. E magna and Eimeria irresidua are the most pathogenic intestinal Eimeria species found in rabbits, and also affect the small intestine.

The clinical signs include weight loss, mild to severe intermittent or continuous haemorrhagic diarrhoea, dehydration and, occasionally, intestinal intussusception. Death is usually associated with secondary bacterial enteritis and dehydration (Fig 5).

Fig 5

(a) Perineal faecal staining in a rabbit with acute-onset diarrhoea. (b) Postmortem examination of the rabbit revealed a fluid- and gas-filled colon. Large numbers of coccidial oocysts were found on cytology

Diagnosis

Coccidiosis is presumptively diagnosed by finding oocysts on faecal flotation. Even repeated faecal examination may reveal only small numbers of oocysts, but it is important to remember that the amount of oocysts does not correlate directly with their clinical significance (ie, the presence of even a few oocysts can cause significant clinical disease). A definitive diagnosis requires histopathological examination of the ileum and/or jejunum, where coccidia may be identified within parasitised epithelial cells. These cells often die, which may lead to ulceration and a mixed polymorphonuclear and mononuclear exudate.

Treatment and prognosis

Treatments for coccidiosis are listed in Table 1. In mild cases, the prognosis is good and the rabbit may develop lifelong immunity.

Bacterial enteritis

Clostridiosis and dysbiosis

The bacteria Clostridium spiroforme, Clostridium difficile and Clostridium perfringens are associated with enteritis and enterotoxaemia in rabbits. Tyzzer's disease is caused by Clostridium piliforme. Clostridium species are widespread pathogenic bacteria but also inhabit the gastrointestinal tract of adult rabbits as part of the normal intestinal flora, along with Bacteroides, Enterococcus, Staphylococcus and Enterobacter species and Escherichia coli.

Disease in adult rabbits may develop as a result of dysbiosis. The predisposing factors involved in caecal dysbiosis include:

  • A sudden change in diet altering the caecal pH and motility;

  • Stress, causing immunosuppression and decreased gastrointestinal tract motility;

  • Administration of antibiotics, causing suppression of the normal microbial flora. The PLACE mnemonic (see Box 2) can be used to remember which antibiotics to avoid in rabbits, as they can be associated with fatal enterotoxaemia, especially if given orally.

Box 2: PLACE mnemonic for antibiotics to avoid in rabbits

P: Penicillins

L: Lincosamides

A: Aminoglycosides

C: Cephalosporins

E: Erythromycin

Bacteria such as Bacteroides species normally exert an inhibitory effect on potentially pathogenic bacteria including Clostridium species and coliforms.

Disease in neonatal rabbits and weanlings may be associated with a high gastric pH of 5 to 6·5, which allows clostridial proliferation and an underdeveloped population of normal gastrointestinal microbial flora. In young rabbits aged one to two months, diversification of the antibody repertoire has been shown to rely on interactions between the gut-associated lymphoid tissue and specific members of the normal gastrointestinal microflora. Tyzzer's disease has been associated with the stress of overcrowding, unsanitary conditions and concurrent disease.

Rabbits with dysbiosis may show:

  • Anorexia;

  • Depression;

  • Dehydration;

  • Hypothermia;

  • Intermittent or continuous diarrhoea with haematochezia and mucus.

In acute cases, enterotoxic shock and death can occur within 24 to 48 hours. Chronic cases are occasionally seen, and are characterised by intermittent diarrhoea and weight loss.

Diagnosis

A presumptive diagnosis of dysbiosis can be made based on a history of recent antibiotic administration, a change of diet or stress.

Treatment and prognosis

Aggressive fluid and supportive therapy are essential in rabbits with dysbiosis, which are likely to be in a critical condition. Cholestyramine has been shown to bind to bacterial toxins, including clostridial cytotoxin and endotoxin, in humans. Loperamide hydrochloride and a high-fibre diet can improve the recovery.

The role of probiotics in these cases is still being studied, but transfaunation by administering fresh caecotrophs from healthy rabbits can provide the appropriate microflora to help re-establish caecal homeostasis (see Box 3). The prognosis for recovery of mild cases, which can be treated with dietary adjustments, can be good, but severe cases have a poor prognosis.

Box 3: Transfaunation

  • Place an Elizabethan collar on a donor rabbit overnight to prevent coprophagy

  • Collect the caecotrophs produced by the donor and place them directly into the diastema of the mouth of the sick rabbit

  • If the rabbit refuses them, mix the fresh caecotrophs with a small amount of water and administer the suspension orally by syringe

  • Administer a small number of caecotrophs (five to 10) every three hours

Colibacillosis

The presentation of colibacillosis in rabbits is variable and depends on the particular strain of E coli, as well as on the presence of concurrent infectious agents. The rabbit enteropathogenic E coli (rabbit EPEC or RDEC-1) strain is the most common cause of bacterial enteritis in this species. Transmission is by the faeco-oral route. Neonatal rabbits aged one to 14 days, or young animals between two and four months, that are stressed by weaning, transport or overcrowding, are most likely to be clinically affected. The clinical signs include acute weight loss and diarrhoea, intussusception and rectal prolapse. Mortality ranges between 50 and 100 per cent.

Salmonella species, Pseudomonas aeruginosa, Yersinia pseudotuberculosis and Lawsonia intracellularis can also cause acute or chronic enterocolitis in rabbits. Neonates and weanlings are most severely affected, and the morbidity and mortality can vary. Transmission is by the faeco-oral route or via contaminated feed or water. It is important to be aware that such infections have zoonotic potential.

Diagnosis

Colibacillosis can be diagnosed presumptively by isolating E coli in the faeces of affected animals, although dysbiosis often causes the proliferation of non- pathogenic E coli. A definitive diagnosis is based on histopathological identification of E coli attachment to enterocytes.

In cases where Salmonella species, P aeruginosa, Y pseudotuberculosis or L intracellularis are suspected, the diagnostic laboratory must be informed, as specific enrichment and selection procedures are recommended for faecal bacterial culture and sensitivity testing of these organisms.

Treatment and prognosis

Affected animals should be treated with broad- spectrum antibiotics while the results of bacterial culture and sensitivity testing are pending. Early, aggressive fluid and supportive therapy, including the administration of loperamide hydrochloride, is essential to increase the chances of a successful outcome. The prognosis is guarded to poor but will depend on the strain of bacteria involved, the immunocompetence of the patient and the presence of synergistic copathogens, such as rotavirus.

Viral enteritis

Viral enteritis is primarily seen in young weanling rabbits. Coronavirus has been reported to affect animals 21 to 70 days of age, and rotavirus is most common in rabbits aged 30 to 80 days. These pathogens are transmitted by the airborne and faeco-oral routes. Viral infection causes villous atrophy with lymphocytic inflammation, particularly in the ileum, and intestinal distension.

Maternal antibody to rotavirus can provide some protection in young rabbits, resulting in subclinical shedding of virus for about three days. Soft to diarrhoeic faeces are often the main clinical sign of rotavirus infection. Coinfection with rotavirus and E coli has been shown to result in an increased mortality of 50 to 80 per cent due to diarrhoeal disease (Thouless and others 1996). Coronavirus infections are associated with high morbidity and mortality.

Diagnosis

Rotavirus infection can be diagnosed on virus isolation, the detection of specific antibodies or histopathology. A definitive diagnosis of coronavirus can be made on histopathology or isolation of virus in the faeces. However, both rotavirus and coronavirus can be found in clinically normal adult rabbits.

Treatment and prognosis

Supportive treatment of rotavirus infection is usually successful, except in cases of simultaneous coinfection with another enteropathogen, which carries a guarded prognosis. Coronavirus enteritis has a guarded to poor prognosis.

Mucoid enteropathy

Mucoid enteropathy (also called rabbit epizootic enteropathy) is an idiopathic condition that results in goblet cell hyperplasia and excessive mucus production within the intestinal tract. The condition is mainly seen in young rabbits aged from four to 14 weeks, although there have been reports of cases in older animals. It may occur concurrently with other enteropathies. Lesions of mucoid enteropathy have been found in association with caecal hyperacidity due to abnormal volatile fatty-acid production or absorption, dysbiosis, a fibre-deficient diet and dysautonomia.

The clinical signs that have been reported in cases of mucoid enteropathy include:

  • Anorexia;

  • Depression;

  • Abdominal pain and distension;

  • Weight loss;

  • Dehydration;

  • Hypothermia;

  • Diarrhoea initially, progressing to mucus excretion; or

  • Constipation and palpation of a firm, dough-like, large caecum.

Acute mortality can occur within one to three days, reaching rates of 30 to 80 per cent. In chronic disease, mortality may occur within seven to nine days.

Diagnosis

A presumptive diagnosis of mucoid enteropathy can be made on the history and clinical signs, although the condition can mimic other enteropathies. Radiography may reveal evidence of caecal impaction and, in more advanced cases, evidence of gastric and intestinal stasis. A definitive diagnosis is made on postmortem findings of copious intestinal mucus and goblet cell hyperplasia.

Treatment and prognosis

Non-specific supportive treatment is recommended for affected animals, but the prognosis is poor. Feeding a high-fibre and low-carbohydrate diet can help to prevent mucoid enteropathy from developing.

Dysautonomia and caecal impaction

Dysautonomia in rabbits is an idiopathic condition that causes a loss of function of the autonomic nervous system. The condition is associated with signs of gastrointestinal stasis and autonomic nerve deficits. Clinical signs include:

  • Dry mucous membranes and conjunctiva;

  • Dilated pupils;

  • Bradycardia;

  • Urine retention and overflow incontinence;

  • A dilated, firm, impacted colon;

  • Proprioceptive deficits;

  • Loss of anal tone.

Accumulation of food in the mouth, dysphagia and evidence of lower respiratory disease due to aspiration pneumonia, secondary to dysphagia and megaoesophagus, may also be seen. As in other species, such as hares and horses, dysautonomia in rabbits is associated with high mortality.

Diagnosis

Dysautonomia can be diagnosed presumptively based on the clinical signs. Radiography of the thorax and abdomen may reveal evidence of aspiration pneumonia, megaoesophagus, an impacted colon and a large bladder. The absence of tear production can be demonstrated using a Schirmer tear test; the average tear production in healthy rabbits is 5 ± 2·4 mm/minute (Abrams and others 1990). A definitive diagnosis requires postmortem histology and electron microscopy.

Treatment and prognosis

Rabbits with dysautonomia should receive supportive treatment, including fluid therapy, force-feeding, lubricating the eyes, the use of enemas and emptying the bladder. The prognosis in rabbits is poor, although some animals of other species have spontaneously recovered.

Intestinal neoplasia

Anorectal papillomas are well-differentiated benign tumours and are not related to viral papillomas of the skin and oral cavity. They are small, friable, fungating masses that originate from the rectal squamous columnar epithelium at the anorectal junction. The clinical signs include constipation, discomfort, haemorrhage from the anus and, in severe cases, rectal prolapse; some affected rabbits may be asymptomatic.

Neoplastic infiltrations, including lymphomas, adenocarcinomas, leiomyosarcomas and metastatic haemangiosarcomas, have been reported as spontaneous neoplasms of the intestinal tract in several breeds of rabbit. Metastasis of uterine adenocarcinomas across the peritoneal cavity has also been reported. Some rabbits may show no clinical signs until the disease is advanced and sudden death occurs. Clinical signs that may be seen in animals with intestinal tumours include:

  • Diarrhoea;

  • Gastrointestinal ileus or obstruction;

  • Anorexia;

  • Ascites;

  • Emaciation;

  • Depression;

  • Pallor;

  • Cutaneous nodules (in cases of lymphoma);

  • Peripheral lymphadenopathy.

Enlarged abdominal lymph nodes causing compression of the intestines may also be seen in rabbits with lymphomas.

Diagnosis and treatment

Anorectal papillomas are usually presumptively diagnosed based on the clinical features, but excisional biopsy and histopathology are required for a definitive diagnosis. Surgical excision of anorectal papillomas is curative, provided all of the abnormal tissue is removed. In asymptomatic cases, spontaneous regression can occur. The prognosis for a full recovery is good.

Infiltrative neoplasias may require more extensive diagnostic investigation. Lymphocytosis may be seen on routine haematology and, in such cases, lymphoma should be suspected. Thoracic and abdominal radiographs may reveal a primary tumour or metastasis. Barium enemas may aid the diagnosis of a space-occupying lesion in the colon. Ultrasonography can be used to demonstrate the normal layering and thickness of the intestines, provided there is not too much gas in the intestines causing shadowing. Prominent mesenteric lymph nodes and regional abnormalities, and small peritoneal effusions, suggesting infiltrative disease, may also be found on ultrasonography. Biopsy and histopathology is required for a definitive diagnosis. Biopsies may be obtained endoscopically from the distal colon. Laparotomy or laparoscopy will be required to obtain biopsies from the small intestine, caecum or proximal colon (Fig 6).

Fig 6

Image of the abdomen of a rabbit taken using a laparoscopic camera, showing the duodenum (D), pancreas (P) and caecum (C)

Cases of infiltrative neoplasia could be treated by chemotherapy, extrapolating the protocols used in cats and dogs. As with gastric neoplasias (see Part 1), the prognosis will depend on the stage of the disease when it is diagnosed and the response to treatment.

Summary

Appropriate investigation of the clinical signs of intestinal disease in rabbits, and specific treatment of the underlying cause, is vital to achieving an optimum outcome in these animals, which, as with all prey species, will actively hide signs of disease.

Self-assessment test: Intestinal diseases in rabbits

  1. Which nematode that is considered to be non-pathogenic is commonly seen in rabbits?

  2. What are the common species of intestinal coccidia in domestic rabbits?

  3. What are the common predisposing factors involved in caecal dysbiosis?

  4. List the antibiotics that should be avoided in rabbits, as they can be associated with fatal enterotoxaemia, especially if given orally.

  5. List the types of neoplasia that have been seen in the intestines of rabbits.

Answers

  1. Passalurus ambiguus

  2. Eimeria perforans, Eimeria media and Eimeria magna

  3. A sudden diet change altering pH and gastrointestinal motility, stress causing immunosuppression and decreased gastrointestinal motility, or antibiotic administration causing suppression of the normal microbial flora

  4. Penicillins, lincosamides, aminoglycosides, cephalosporins and erythromycin

  5. Anorectal papillomas, lymphomas, adenocarcinomas, leiomyosarcomas and metastatic haemangiosarcomas

References

Further reading

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Footnotes

  • Provenance Commissioned and peer-reviewed

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