Dear Christopher Cat: I recently adopted a kitten who sneezes and has a runny nose. Her veterinarian diagnosed an upper respiratory infection but said an antibiotic wasn’t needed. I thought antibiotics cured infections. Why didn’t he prescribe one?

Christopher Responds: Almost all kitten upper respiratory infections (URIs), essentially head colds, result from feline herpes and calici viruses. Antibiotics have no effect on viruses, and sometimes they cause unpleasant side effects, such as loss of appetite, diarrhea and vomiting.

If you ask, your veterinarian probably will tell you he didn’t prescribe an antibiotic for those reasons.

Your kitten’s immune system likely will overcome the viruses, just as your human immune system kills the viruses that cause your colds.

Sometimes, though, URI viruses damage the respiratory tract enough that underlying bacteria thrive. In that situation, antibiotics may be helpful in treating clinical signs involving the nose, sinuses, eyes and mouth. Your veterinarian knows best whether an antibiotic is warranted.

Upper respiratory infections can be prevented by periodically vaccinating all kittens and adult cats.