URINARY TRACT BACTERIAL INFECTIONS IN HORSES

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Causative Agent(s)

Usually, urinary tract infections (UTI) are ascending secondary infections due to multiple bacterial organisms such as Escherichia coli, Klebsiella spp., Proteus spp., Enterobacter, Pseudomonas spp., Staphylococcus spp., and Streptococcus spp. Most often, UTI sequels mechanical obstructions and/or impairment of normal urine flow. Consequently, there is the need to also address the underlying cause of this disease.

Clinical Presentation and Epidemiology

Common clinical conditions associated with UTI in horses are cystitis, pyelonephritis, and interstitial nephritis. General clinical presentation are haematuria and lack of control over urination resulting to frequent and/or excessive urination, urine dribbling, and scalding. In addition, horses with pyelonephritis could develop fever and experience pains around the kidneys resulting to straining while urinating. Pyuria is considered as one of the diagnostic biomarkers pathognomonic of UTI; however, presence of many leucocytes in urine of mares that have recently foaled is not uncommon. Urinary tract infections (UTI) are infrequent in horses, but then when they occur, bacterial organisms are mainly the implicated infectious agents. Mares are more predisposed to UTI as compared to stallions because the former have a shorter urethra and potential for faecal contamination from poor perinea conformation.

Diagnostic Considerations

As a guiding principle, antibacterial selection for treating suspected cases of UTI should be based on results from bacterial culture of urine samples obtained by cystocentesis (catheterisation) and bacterial susceptibility tests.

Management and Treatment

Empirical antibacterial treatment with potentiated sulphonamide (trimethoprim/sulphamethoxazole) is recommended in a ratio of 1/5 (trimethoprim/sulphonamide) when the clinical condition is not life threatening. Also, the choice of antibacterial drug should be based on its pharmacokinetic properties, e.g., antibacterial drugs that would present a high concentration in the urine or mainly eliminated through the urine are recommended for treating cystitis and other forms of UTI. But in a situation where the bladder wall and/or tissues of the kidneys are involved (e.g., pyelonephritis), drugs that are well distributed into kidney tissues should be considered. It is worth nothing that sulphonamides are not effective in the presence of purulent materials because of the freely available para-aminobenzoic acid from dead neutrophils. Consequently, it is contraindicated in UTI presented with pus discharges.

Trimethoprim/Sulphamethoxazole: 30mg/kg, q12h x 14 days, PO. or

15mg/kg, q12h x 7 days, slow IV infusion.

Trimethoprim/Sulphadoxine: 20mg/kg, q12h x 14 days, IM.

Gentamicin sulphate: 6mg/kg, q24h x 5 days, IM; or 4mg/kg, q24h X 5 days, IV. Nitrofurantoin: 10mg/kg, q12h x 5 days, PO.