Dr. Christine Merle, a veterinarian at the University of Illinois College of Veterinary Medicine in Urbana, says, "While dogs do get urinary tract infections, cats are much more susceptible." Female cats are also more susceptible than male cats. This may be because the urethra (opening from the bladder to the outside world) is very short in female cats, and it is close to the rectum, where there is a large amount of bacteria. In addition, cats do more grooming than dogs, which can spread bacteria.
Dogs are usually housebroken, and because they go outside, there is more opportunity for an owner to notice when there is a problem.
The owner may notice straining or blood in the urine sooner. Infections often go unnoticed in cats because the owner may not see the cat using the litter box. Often, cat owners don't notice there is a problem until their pet stops using the box. Dr. Merle says, "While some cats stop using the litter box for behavioral reasons, it is important to rule out a medical problem before assuming that the cause is behavioral."
Since urinary tract infections can be caused by a multitude of factors, it is often difficult to discover the cause. The origin of an infection could be as simple as an overgrowth of bacteria or as complicated as bladder stones.