There are many conditions which can affect the urinary tract including urinary tract infections (UTIs), urinary incontinence, bladder or urethral stones, cystitis, cancer or trauma to the urinary tract. In some cases, particularly if your pet is straining to urinate or crying in pain, urgent medical attention is advised as can life-threatening if left untreated.
Bacterial UTIs are one of the most common infectious diseases and can affect up to 14% of all dogs during their lifetime. Pathogenic, or disease-causing, bacteria are most commonly derived from faecal flora from contamination, but may also result from skin flora and most commonly gain access by colonisation of skin around the anus and external genitalia resulting in ascending infection. While the kidneys, bladder and proximal urethra are normally sterile, the distal urethra and external genitalia normally have commensal bacterial flora. The risk of infection is related to an imbalance between host defences and ability of bacteria to enter the URT and multiply.
The urinary tract has several host defence mechanisms in place to prevent infections. Mucosal (the lining of the urinary tract) defensive barriers include antibody production, surface glycosaminoglycan layer, intrinsic antimicrobial properties and bacterial commensal population which compete with other potential pathogens. Exfoliation of cells in the lining of the urinary tract also helps prevent colonisation.
In terms of sex predisposition, female dogs tend to be more susceptible to urinary tract infections due to their inherent anatomical design; the female urethra is short and wider allowing bacteria to more easily ascend and cause infection.
Urinary tract infections can occur within the upper urinary tract, consisting of the kidneys and ureters and the lower urinary tract, comprised of the bladder and urethra. Both can present with a different set of clinical signs which will be investigated by your veterinarian.
The table below indicates the clinical signs consistent with both upper and lower urinary tract conditions
Abnormal renal palpation or renal/lumbar pain
Lower Urinary Tract
Your veterinarian is likely to suggest submitting a urine sample from your pet, ideally first urination in the morning as this will be the most concentrated and hopefully a sufficient volume to be analysed. Your vet is likely to recommend a full urinalysis including a dipstick to measure glucose, bilirubin and white blood cells amongst other parameters to aid diagnosis and to help rule out other confounding factors such as diabetes.
Taking a urine specific gravity gives an indication of kidney function by assessing the ability to of the kidneys to concentrate the urine. Examination of sediment in the urine is also complementary and helps to indicate if infection is present.
Examination of the sediment under the microscope is often undertaken to identify excess white blood cells, and in particular, those that have engulfed bacteria and are therefore present within the white blood cells. This is often indicative of active infection but does not necessarily confirm the source of infection.
Based on staining of bacteria and pattern it might be possible to interpret a likely causative agent and thus empirical treatment can be implemented. In some cases, this may be difficult to determine as contamination from the external genitalia and skin within the free catch sample can misinterpreted.
Gold standard is a cystocentesis sample (most often conscious) which can be performed with ultrasound to guide the needle attached to a syringe into the bladder to obtain a more sterile sample. In some cases, it can be possible to take a sample based on palpation of the bladder alone, especially when full. This has the main advantage in that a bladder scan can also be performed to rule out other causes such as bladder stones or whether there is a mass present.
Another alternative would be placing a urinary catheter but this tends to have to be placed under general anaesthetic as not usually tolerated.
After achieving a diagnosis that your dog has a urinary tract infection, your veterinarian is likely to prescribe a short course (typically 10-14 days) of broad-spectrum antibiotics.
Should no response be observed in 7 days then your vet may recommend an alternative antibiotic guided by culture and sensitivity of a urine sample.
If your pet develops recurrent UTI then a blood sample may be recommended to check for any underlying disease that may predispose your pet to a UTI, this can include conditions such as diabetes where there is increased glucose in the urine as well as immunosuppressive disorders such as Cushing’s disease which can compromise host immune defences.
References: (1) BSAVA manual of nephrology and urology | (2) MSD MANUAL Veterinary Manual | (3) FETCH by WebMD
