Urinary tract disease is a common presentation in companion rabbits and guinea pigs. While some presentations such as haematuria can be associated with the reproductive tract, this article focuses on the urinary tract in particular.
Any rabbit or guinea pig presenting with urinary abnormalities should have a diagnostic work-up similar to that of our cat and dog patients. A urinalysis should be performed as a minimum, ideally with urine sediment cytology as well, to assess for any evidence of bacterial infection or true haematuria. This is particularly important in rabbits as they are able to excrete porphyrin in their urine which can cause a colour change ranging from red to dark brown or orange (Di Girolamo and Selleri, 2020). Porphyrinuria is a benign condition usually caused by pigments in the diet and self-resolves within three to four days. Gentle centrifugation can also help determine porphyrinuria from haematuria: centrifuging a sample of urine with porphyrinuria will result in no colour change, whereas in cases of true haematuria, gentle centrifugation will separate a layer of erythrocytes from clear urine.
A urinalysis should be performed as a minimum, ideally with urine sediment cytology as well, to assess for any evidence of bacterial infection or true haematuria
A free-catch urine sample can be obtained from rabbits and guinea pigs via gentle manual expression of the bladder, or ideally an ultrasound-guided cystocentesis sample can be taken under sedation or general anaesthesia.
Further diagnostics can involve ultrasonography of the bladder to assess for changes to the bladder wall, presence of uroliths or “sludge” within the bladder lumen or evidence of hydroureter. Radiographs can be useful to identify the presence of uroliths; however, care must be taken to adequately sedate the patient and extend the hindlimbs in both rabbits and guinea pigs, as sesamoid bones of the stifle joints can be mistaken for urolithiasis when the legs are superimposed over the caudal abdomen.
Hypercalciuria, bladder “sludge” or bladder “sand” is a common presentation in rabbits. These rabbits will pass turbid urine that dries as a white or beige smear; however, on manual bladder expression, they often pass thick, sludgy urine (Figure 1). Affected rabbits may be asymptomatic or show signs of anorexia, dysuria, stranguria, weight loss, tooth grinding and lethargy. Most affected rabbits are overweight, have limited exercise and are fed diets with large amounts of pellets, calcium-rich vegetables and hay high in calcium (Di Girolamo and Selleri, 2020).
An evaluation of diet is very important, as rabbits have a unique calcium metabolism that increases their risk of hypercalciuria. Rabbits passively absorb calcium from the intestines via a concentration gradient between the intestines and blood, independent of Vitamin D3 regulation (Eckermann-Ross, 2008). Increased intestinal calcium absorption increases calcium excretion via the kidneys, and fractional excretion of calcium of between 45 and 60 percent has been reported (Di Girolamo and Selleri, 2020). When the kidneys’ resorption capacity is exceeded, calcium precipitates in the urine as calcium carbonate, which builds up over time within the bladder lumen.
Radiographs of the caudal abdomen are a useful diagnostic tool, as the calcium carbonate “sludge” sits as a radiopaque shadow in the gravity-dependent area of the bladder lumen
Radiographs of the caudal abdomen are a useful diagnostic tool, as the calcium carbonate “sludge” sits as a radiopaque shadow in the gravity-dependent area of the bladder lumen (Figure 2). Ultrasonography should be used to confirm the presence of bladder “sludge”, which often appears as heterogenous swirling material within the bladder lumen, as well as to identify if any uroliths are present within the “sludge” itself. Urinalysis will show crystalluria, often accompanied by proteinuria and haematuria (Di Girolamo and Selleri, 2020). This can also help to identify the presence of bacteria; however, this should be interpreted with caution in free-catch samples.
Urethral catheterisation under sedation or general anaesthesia to perform gentle bladder lavage with warmed sterile saline can be utilised to flush the bladder of the “sludge” (Mancinelli and Lord, 2014). Bladder lavage should be continued until the urine is clear (Figure 3). Following this, husbandry changes should be implemented to prevent recurrence. These include reducing but not completely removing calcium levels in the diet, increasing water intake, encouraging weight loss in overweight rabbits and assessing the need for analgesia in older rabbits that may have degenerative joint disease preventing them from exercising (Di Girolamo and Selleri, 2020).
Urolithiasis is seen in companion rabbits but is a more common problem in guinea pigs. Guinea pigs presenting with uroliths are often over two years of age and are evenly represented between sexes (Pignon and Mayer, 2021). The majority (90 percent) of uroliths in guinea pigs are composed of calcium carbonate (Hawkins et al., 2009), compared to 65 percent of uroliths in rabbits (Reavill and Lennox, 2020). Most urinary stones in guinea pigs are seen in the bladder or urethra and often lodge in the bladder neck in male guinea pigs (Pignon and Mayer, 2021). Clinical signs depend on the location of the urolith and include dysuria, stranguria, haematuria, anorexia and a hunched posture with bladder and urethral stones. However, uroliths higher in the urinary tract, such as in the renal pelvis and ureter, often have more vague clinical signs including anorexia, weight loss and abdominal pain, although micturition abnormalities have also been reported.
Because the majority of uroliths in guinea pigs are composed of calcium carbonate, radiographs are ideal to assess for uroliths within the urinary tract (Figure 4). Radiographs are especially important to assess for any smaller uroliths within the urethra if a larger stone is identified within the bladder lumen.
Medical treatment is often unsuccessful, with cystotomy to remove the bladder stone currently the recommended treatment for larger cystoliths, although cystoscopic removal has been reported for smaller cystoliths in females (Pignon and Mayer, 2021). Unfortunately, recurrence rates for guinea pig uroliths are high, with the author observing recurrence as early as eight weeks post-operatively, and owners should be informed of this risk prior to surgery. Bacterial cystitis has been associated with urolithiasis in guinea pigs, so the author recommends culture of the urolith and a sample of urine taken at the time of surgery for appropriate antibiosis if required. Following surgical removal, dietary modification should be implemented as described above for rabbits, to reduce the calcium content of the diet. Potassium citrate has been described to prevent precipitation of calcium within the bladder and increase the pH of urine (Hoefer and Latney, 2009); however, its efficacy is unclear given that guinea pigs have naturally alkaline urine.
Encephalitozoon cuniculi is a common protozoan parasite infection, transmitted in rabbits by the urine-oral route, usually from doe to kits (Di Girolamo and Selleri, 2020). Disease states range from sub-clinical to ocular signs, neurological signs and/or urinary signs. Spores migrating to the kidneys result in non-suppurative granulomatous nephritis which can progress to interstitial fibrosis with chronic infections; however, clinical signs of urinary incontinence are associated with spinal lesions rather than renal lesions (Di Girolamo and Selleri, 2020).
Paired serological titres are recommended to assess for exposure to the parasite, as elevated IgM has been shown to be an indicator of early infection, and rising IgM and IgG titres are indicative of an active infection
Paired serological titres are recommended to assess for exposure to the parasite, as elevated IgM has been shown to be an indicator of early infection, and rising IgM and IgG titres are indicative of an active infection (Keeble, 2014). Serological sampling should be repeated following a 28-day course of fenbendazole to assess antibody response and further treatment and serological monitoring performed as required (Keeble, 2014).
Other causes of urinary incontinence or urine scalding include spinal lesions, intervertebral disc disease, spinal fractures or dislocations, or toxoplasmosis (Di Girolamo and Selleri, 2020). Diagnostic imaging and Toxoplasma serology can be useful to determine the cause of urinary incontinence if E. cuniculi has been ruled out.
Investigation of urinary disease in rabbits and guinea pigs should follow a similar diagnostic investigation to that of our companion dogs and cats. Urinalysis with urine sediment cytology is an excellent initial tool, with diagnostic imaging being a useful follow-up if there is suspicion of hypercalciuria or urolithiasis. Urinary disease of rabbits and guinea pigs is often diet and husbandry related and, following diagnosis of urinary disease, a thorough husbandry review should be assessed and any dietary changes should be implemented if required.