Bladder infection (cystitis) in the dog

What is cystitis?

Cystitis is an inflammation of the urinary bladder. In dogs, a bacterial infection is by far the most common cause — this distinguishes dogs from cats, in whom sterile (idiopathic) cystitis dominates [1]. The bacterium E. coli is most frequently encountered, followed by Enterococcus spp., Staphylococcus and Proteus [1].

Female dogs are more often affected due to their shorter, wider urethra. The risk of a complicated infection increases with kidney stones, anatomical abnormalities, hormonal disorders (such as diabetes mellitus or hypothyroidism), immunosuppression or neurological bladder problems [1].

Recognition

Typical complaints are:

• Difficult or painful urination (dysuria/stranguria)
• Frequent urination of small amounts (pollakiuria)
• Blood in the urine (hematuria)
• Cloudy or strongly smelling urine
• Irritation around the vulva in bitches

Diagnosis

The gold standard is a urine culture with antibiogram [1]. Only then is it known which bacterium is causing the infection and to which antibiotics it is sensitive. Urine cytology (sediment examination) is additionally useful: the presence of intracellular bacteria in the sediment is the strongest independent predictor of a positive culture [2].

Do not wait with a veterinary consultation until the complaints worsen — early diagnosis prevents complications and unnecessary antibiotic use.

Treatment: what the evidence says

Antibiotics — strong evidence

Antibiotics are the proven cornerstone of treatment. The ISCAID 2019 guidelines advise basing the choice on local susceptibility data and — once available — on the culture result [1]. In uncomplicated cystitis, shorter courses have been shown to be effective. Prophylactic antibiotic use without clinical indication must be avoided due to increasing antimicrobial resistance [1].

In recurrent infections, Enterococcus spp. and Pseudomonas are more frequently involved. Polymicrobial infections (e.g. E. coli combined with Enterococcus) are associated with higher resistance rates and worse outcomes than infections with a single bacterial species [3].

Cranberry — insufficient evidence

Cranberry extracts are sometimes recommended in humans as prevention. In dogs, clinical evidence of sufficient quality to label this as effective is lacking. Cranberry cannot replace antibiotic treatment.

Probiotics — insufficient evidence

There are theoretical arguments for the use of probiotics to support the microbiome after an antibiotic course, but controlled clinical research in dogs with cystitis is lacking.

Increased water intake

Drinking plenty of water dilutes the urine and promotes flushing of the bladder. This is a useful supportive measure, but does not resolve a bacterial infection.

Supplementary ≠ replacement

In bacterial cystitis, antibiotics based on a culture are the indicated treatment. Supplementary agents can at most be supportive and must never replace a veterinary diagnosis and treatment. Untreated or inadequately treated cystitis can spread to the kidneys (pyelonephritis) — a serious, life-threatening complication.

Sources

[1] ISCAID guidelines — The Veterinary Journal (2019) [2] Urinary Cytology in Canine UTI — Veterinary Sciences (2022) [3] Polymicrobial UTI retrospective study — JVIM (2022)