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What is Pyelonephritis? Symptoms Diagnosis Treatments Links Harpsie's Experiences



What is It?

Pyelonephritis is a bacterial infection of the kidneys. The cat may also have a lower urinary tract infection (UTI) -  in some cases, untreated lower urinary tract infections rise into the kidneys causing pyelonephritis - but not always.  



Since the infection is in the kidneys rather than lower down the urinary tract, if the cat does not also have a UTI, then you may not see the more common signs of a cat straining to urinate, or urinating blood.


With Harpsie's first kidney infection, which came on very suddenly, it was very dramatic so it was obvious that he was ill. He went from being fine in the morning to screaming when I touched him in the afternoon, and his breathing suddenly became laboured.


With the later attacks, the signs were much more subtle, but fortunately I became adept at spotting them. Harpsie would become a little quieter, and sleep more, and sometimes go off his food a little. We would take him to the vet, and nothing would ever grow in a urine culture but Harpsie would always be anaemic.


After a few episodes, Harpsie began to exhibit an unmistakeable symptom whenever he had a kidney infection: he would become incontinent. He would literally pee where he lay. Whilst inconvenient, at least this enabled us to nip the infection in the bud. However, not every cat with a kidney infection will do this.



A urine culture and sensitivity will be taken, though it is relatively common for nothing to grow in a culture if the cat has a kidney infection rather than a lower urinary tract infection. Even with urinary tract infections, nothing may show in a culture: one human study, Establishment of a persistent Escherichia coli reservoir during the acute phase of a bladder infection (2001) Mulvey MA, Schilling JD & Hultgren SJ Infection and Immunity 69(7) pp 4572-9 found that in some cases the bacteria that cause urinary tract infections can burrow so deep into the bladder lining that they cannot be detected in the usual tests. In a later (2004) study reported by Science Daily, researchers found that the bacteria commonly involved in UTIs pass through four distinct developmental stages, including a dormant stage in some cases which may help explain why UTIs often recur.


Ultrasound may be helpful in diagnosing the existence of pyelonephritis, though this can be of limited value in cats with PKD, like Harpsie, whose kidneys already look abnormal.


If your cat has chronic renal failure, pyelonephritis may make the CRF bloodwork look worse whilst it is present. You need to cure the infection before you can know accurately how severe the renal failure is.



If your cat is acutely ill, s/he may need to be hospitalised and placed on intravenous fluids and antibiotics.


In order to be sure that the bacteria are completely eradicated and the infection completely cured, cats with kidney infections require a prolonged course of antibiotics, for four to six weeks or longer. This is because blood flow to the site of most kidney infections is poor, so it can take a while for the antibiotics to reach and kill the bacteria. 


The only antibiotic which worked for Harpsie was Baytril, but it depends upon which bacteria are causing the infection. There is information about various antibiotics here.




Washington State University mentions that antibiotic treatment should continue for at least six weeks in the case of pyelonephritis.

Urinary tract infection (UTI): how to diagnose correctly and treat (2003) is a presentation by Dr C Brovida to the 28th World Congress of the World Small Animal Veterinary Association, and includes information on pyelonephritis.


Harpsie's Experiences


Harpsie developed his first kidney infection (pyelonephritis) in August 2001. He had a history of struvite crystals and feline lower urinary tract disease (FLUTD) which are not necessarily the same as a urinary tract infection, but it is possible that a urinary tract infection rose into his kidneys.


Harpsie was incredibly ill. He had a fever of 106 degrees fahrenheit (over 41 Celsius), which was as high as the thermometer could read, and was so hot that he had to have a fan blowing on him constantly, plus the vet nurses had to sponge him down with cold water every hour. At one point, they thought they would have to shave him in order to get his temperature down properly, but fortunately this was not necessary. He was on IV fluids (a drip)  and IV antibiotics at the vet for four days, and he still had a fever when he came home, though it was lower than it had been. He had lost 20% of his body weight, and was very weak. He was also anaemic - it is relatively common in cats to become anaemic when they have an infection or inflammation. He had little appetite, and growled when touched near his kidneys.


The vet was unable to detect any bacteria in Harpsie's urine, so treating the infection was hit and miss. He would seem to improve when we began a new antibiotic and his fever would reduce, then it would flare up again. We tried three different types of antibiotics before we finally found the one that worked for Harpsie and actually got rid of the infection, Baytril. Baytril is a very effective drug which saved Harpsie's life, and he never had any problems with it, but used at high doses it may cause blindness in some cats. There is more information on safe dosages here


Harpsie proceeded to have several bouts of pyelonephritis over the coming years, whilst at the same time his FLUTD attacks virtually disappeared. It was as if the upper end of the urinary tract - the kidneys - were now having problems rather than the lower end. This was partly because he had PKD, and cats with PKD are particularly prone to pyelonephritis, since the bacteria can burrow deep into the cysts. This burrowing can also make the infection hard to get rid of.


With the later attacks, it was much less obvious that Harpsie was developing an infection, but fortunately I became adept at spotting those subtle early signs. Harpsie would become a little quieter, and sleep more, and sometimes go off his food a little.


After a few episodes, Harpsie began to exhibit an unmistakeable symptom whenever he had a kidney infection: he would become incontinent. He would literally pee where he lay. I had an emergency supply of Baytril which I would start immediately if it was out of normal business hours. We would go to the vet as soon as we could, where, as ever, nothing would ever grow in a urine culture but Harpsie would always be anaemic. Harpsie usually had a four week course of Baytril, but sometimes he needed six weeks worth, and on one occasion he needed an eight week course. It was quite simple in his case to tell if he needed a longer course: if he became incontinent when we stopped the Baytril, we knew he needed it for longer. Of course, we did not give it unless it was necessary though, because we did not want Harpsie to develop resistance to it.


In his last year of life, Harpsie did not have any kidney infections, for which we were grateful. He never did develop resistance to Baytril.





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This page last updated: 9 February 2008


Links on this page last checked: 31 July 2008


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