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Canine urinary tract infections

Author : Josey Killner

Categories : RVNs

Date : November 1, 2008

Josey Killner discusses the various causes and symptoms of UTI presented in dogs

THE canine urinary tract is resistant to infection due to the natural voiding process, whichwashes any bacteria from the urinary tract. The mucosal surface of the urinary bladder alsosecretes mucopolysaccharide, which inhibits the adherence of bacteria. Infection may occurwhen there is disruption to this surface and/or the natural voiding of urine is altered. Thehigh osmolarity and pH extremes of urine also make it a poor host for bacteria. Prostaticand vaginal secretions are also thought to have antibacterial properties.

The urinary tract is separated into two sections. The upper urinary tract contains the kidneys andthe ureters. The lower urinary tract contains the urinary bladder and the urethra.

Similar organisms cause both upper and lower urinary tract infections (UTI), with E coli being themost frequently isolated. Other organisms, including species of Proteus, Staphylococcus,Streptococcus, Enterobacter and Pseudomonas, are seen occasionally. It is less common to findmultiple isolates responsible for UTI.

Other causes of UTI are viruses, fungi, algae and yeast. It is often difficult to establish, by bacterialculture alone, which section of the urinary tract is affected.

Pyelonephritis is the presence of inflammation and usually bacteria in the renal pelvis and may beacute or chronic. Little is known about how pyelonephritis occurs, but it is likely that it is due to anobstruction or decrease in urinary flow, allowing bacteria in the lower urinary tract to ascend. Thisobstruction may be a temporary blockage, urinary catheterisation or a reduction in renal blood flow.

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Pyelonephritis is difficult to diagnose. Acute pyelonephritis may be diagnosed by clinical findings,such as acute onset of painful kidneys on palpation, or enlarged kidneys on palpation orradiography, plus the usual findings in lower urinary tract disease, such as bacteriuria. These signsare, unfortunately, not always present. The diagnosis of chronic pyelonephritis is even moredifficult. Treatment of pyelonephritis is aimed at eliminating bacteria from the kidneys. Thisgenerally proves more difficult than eliminating bacteria from the lower urinary tract and mayinitially require intravenous antibiotic therapy and a prolonged course (four to six weeks) ofantibiotics. Long-term monitoring is indicated to ascertain response to treatment and any relapsesthat may occur.

Cystitis is inflammation of the urinary bladder, and in the dog is often associated with UTI, althoughit may be caused by uroliths, with no bacterial presence. Idiopathic cystitis rarely occurs in the dog.Palpation may reveal a thickened bladder, discomfort and/or contraction of the bladder.

Catheterisation

There is a high risk of UTI occurring with catheterisation of the urinary bladder. Bacteria may beintroduced into the bladder by bypassing the host defence mechanisms. This can occur throughtransport of bacteria into the bladder on the catheter, retrograde flow of urine via the catheter fromthe collection bag, or bacteria moving between the catheter and the mucosal lining of the urethra.

Care should always be taken when inserting a urinary catheter to ensure strict asepsis is adheredto, it is lubricated and a soft catheter is used. Dogs with indwelling catheters with a closedcollection system still have a high potential for developing UTI, and this is increased with opencatheterisation. The catheter should be removed as soon as possible to limit the potential ofascending bacteria. Re-catheterisation also increases the risk of infection and should be limited.Due to the high degree of association between urinary catheterisation and UTI, it is wise to performurinary culture and sensitivity after catheter removal.

Female dogs are more predisposed to UTI than males due to their wider, shorter urethra, and theproximity of the external opening to the rectum. Commensal bacteria may travel from the rectumand infiltrate the urinary tract.

There is a range of clinical signs associated with urinary tract infections, including:

• dysuria (difficulty urinating);

• anuria (unable to pass/produce urine);

• polyuria (increased quantity of urine passed);

• pollakiuria (increased frequency of urination);

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• haematuria (blood in the urine);

• dribbling urine;

• licking at vulva or prepuce;

• depression; and

• pain/discomfort/irritation.

Most urinary tract infections ascend from the distal portion of the urethra, which is the only part ofthe urinary tract that is not sterile. Pathogens may pass into the urethra from the perineum, or evenby veterinary intervention from catheterisation.

Diagnosis

Diagnosis of a urinary tract infection can be made from urinary analysis. Urine should be collectedby cystocentesis (via a needle and syringe inserted through the abdominal wall and into thebladder). Urine collected “free flow” when the patient voids urine voluntarily, or even by catheterplacement, may be contaminated with bacteria from the distal section of the urethra, or from thearea around the urethral opening or anus, and therefore does not reflect the content of the bladder.

Cystocentisis can only be performed if the bladder is palpable through the abdominal wall. Manypatients with UTI urinate frequently and so rarely have a large quantity of urine in the bladder.Cystocentisis can be performed on a patient without chemical restraint, but the patient must remainstill to reduce the possibility of damage to the bladder or other abdominal contents. If required, asedative may be given.

The patient should be held in lateral recumbency or standing. A 20ml syringe and a 23g needleshould be prepared. A smaller syringe can be used, especially if the bladder is small, but a boricacid urinary container, which should be selected for culture and sensitivity tests, requires 20ml ofurine and should never be under-filled as this reduces the effectiveness. Once the urine has beencollected it can be placed in a sterile container. If this is less than the volume required to fill a boricacid pot it should be placed in a plain, sterile container and labelled with the patient and client’sname and the date. This can then be wrapped in cotton wool and placed in a sealable plastic bagto prevent spillage and contamination in transit. A laboratory form should be filled out and placedwith the sample. This can then be placed in a jiffy bag or container provided by the externallaboratory for dispatch. If the sample is not to be collected or posted until the following day then itshould be placed in a refrigerator.

Tests

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Urinary tests that can be performed in-house are a urinary dipstick, specific gravity, andmicroscopy. Urinary dipsticks will usually give indications as to the pH, protein, blood content,blood glucose and ketones of urine. The specific gravity on dipsticks is not reliable. None of thesetests are diagnostic for UTI but may give some indication that one is present or that the patient hasother problems.

Before opening the dipstick pot, check it is still in date. Wearing gloves, remove a stick from the potand immediately replace the lid to avoid contamination of the remainder of the sticks. Place thestick on a clean tissue on the laboratory work surface. Urine can be dripped onto each part of thestick via a syringe or pipette. Each stick or section on the stick can be read after a specific length oftime, usually between 15 and 60 seconds. The results should then be recorded.

A refractometer should be used for reading the specific gravity of urine. This provides theconcentration of the urine. The refractometer should first be calibrated by placing a drop of wateron the viewing lens. Looking through the eyepiece it should read zero. Dry this off using a softtissue and replace it with a drop of urine. Looking through the eyepiece will give the specific gravityreading for the patient’s urine. The specific gravity of a dog’s urine should be between 1.035 and1.055. If the specific gravity is below 1.035 the urine is dilute; if it is above the higher referencerange the urine is concentrated.

Examination of the urine sample under a microscope requires careful preparation. The urine shouldbe placed, aseptically, into two bullet tubes. They should be balanced in a centrifuge and spun at1-2,000 rpm (depending on the radius of the centrifuge) for three to five minutes. Once thecentrifuge has stopped the supernatant should be disposed of and the sediment resuspended byflicking the tube gently. Using a small pipette, withdraw a drop of urine from the remaining sampleand place it on a clean, dry microscope slide. Place a cover slip on top of the sample and wait untilit settles. Using a magnification of x10 and, subsequently, x40, examine the sample under amicroscope. If the urine is infected you may be able to identify bacteria and white blood cells. If aninfection is present the urine may also contain red blood cells and epithelial cells.

Damage may be inflicted on the mucous membrane of the urinary bladder or urethra by uroliths(stones) or crystals, which have rough surfaces. Minerals found in the urinary tract adhere andcrystals are formed. These crystals may consequently adhere to each other and form uroliths. Thequantity of minerals in the urinary tract may have increased due to a poor diet (high in magnesium,phosphorus, calcium or protein), reduction in water intake or reduced ability or inability to voidurine. They may also form when the pH is alkaline (greater than 7.4) or acidic (lower than 6.8).Infection may then occur due to a lowered resistance from the damaged mucous membrane.

Dogs with crystalluria and urolithiasis do not always develop a concurrent infection and, therefore,may not require antibiosis. Struvite uroliths may be formed as a result of a UTI due to the elevationin concentrations of ammonium and carbonate in an alkaline environment, caused by the infection.Treatment is then aimed at eradication of the UTI by culture and sensitivity-based antibiotic

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treatment and dissolution of the struvite by feeding a calculolytic diet (for example, Hill’s S/D) or asupasaturation diet (for example, Royal Canin urinary tract). Once the struvite has been dissolvedand the UTI successfully treated, a normal diet may be introduced.

Glucocorticoids may predispose a dog to UTI. This may be due to the reduced antibacterialproperties of urine. Dogs suffering from hypercortisolism are also at risk and routine urine culturefrom these patients is indicated.

Patients with a suppressed immune system are predisposed to develop other diseases, includingUTI. These include diabetics, patients on chemotherapy, and hospitalised patients with otherdebilitating diseases, the very young and the elderly. Glucosuria and polyuria, as found in thediabetic, may also predispose the dog to UTI. As a nurse caring for these patients it is importantthat we are aware of the potential problems.

Haematuria is among the signs that a dog may have a UTI.

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A pyelonephrotic kidney. Pyelonephritis is the presence of inflammation and usually bacteria in therenal pelvis, and it may be acute or chronic.

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A distended bladder in a dog.

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Contrast radiographs of the urinary system.

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Contrast radiographs of the urinary system.

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Left: Performing cystocentesis cranial to the left, caudal to the right.

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Right: Microscopic view of urine sediment showing bacteria and white blood cells, which canindicate a urinary tract infection.

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