When you get a dog, you know you'll probably have to part with it sooner than you'd like. What you don't bargain for is to have to put it down when it's only 5, then face the possibility that you might have killed that trusting little soul with kindness.

That happened to me in early March when I found myself, one snowy morning, standing in a veterinary emergency clinic, praying for the vet to come in and end the too-short life of my beloved 5-year-old pug, Hanna.

After seven days of seizures, hundreds of dollars of treatment and buckets of tears, the time had come to end her life.

She had recently been given a yearly booster shot to protect against distemper and developed what we believe to have been PDE or Pug Dog Encephalitis, which can strike any pug.

Did the shot trigger the onset of the disease? That's something we don't know. But what we do know is that shortly before her death the dog had a shot that was completely unnecessary, according to the scientific protocols taught by many of the finest veterinary teaching institutions.

While statistics say that it is extremely rare for a dog to die from a booster shot, if it's your dog, and you held her in your arms while her life drained away, that statistic means very little.

Should you stop getting your pet booster shots? Certainly not. Diseases such as parvovirus and distemper pose very real threats to the pet population, but the threat of problems, not all of them fatal, from overimmunization is also a real and understudied problem in the pet world, especially in breeds such as pugs, which have problems that may be triggered by shots. Pets that are elderly, in ill health or have seizure disorders should also have limited boosters, according to experts.

So if you do nothing more, question the necessity of yearly boosters and open a dialogue with your vet about the three-year protocols. Think of it as Hanna's legacy.

Dr. Jamie Bush is researching Pug Dog Encephalitis at Colorado State University. PDE is an always-fatal seizure disorder. The illness is poorly understood, poorly documented and widely unknown, even among pug owners. There is no treatment, and all pugs have some risk until about the age of 8. Dr. Bush's research is examining environmental triggers. She is collecting data, which she shares with a colleague who is studying the genetic aspects of the disease at Texas A&M University. The researchers are seeking dogs and specimens from dogs that may have died from PDE. Those with questions on PDE can e-mail Dr. Bush at pugology@lamar.colostate.edu.