Dog Bites

So this last Friday, my brother was bitten by a stray dog. He was out walking our dog, Dante, and the stray wanted to attack. Unfortunately, Tony was stuck in the middle and the stray did some serious damage to his arm with more than 10 large puncture and tear sites along with a fractured wrist. As the over protective brother of a special needs man I reacted rather quickly in getting this animal away. The whole incident lasted about 20 seconds. In thinking about it initially, I started to wonder what did I do wrong? What could I have done differently? Well now that I'm more rational and he's been treated by the hospital and is on his way to healing I have to wonder how did stray dogs become so prevalent lately? (Both of my brothers and my mother have been attacked in different locations by a stray dog in the last 2 years). This seems to be a growing problem and I'm at a loss as to how to begin working on it. Suggestions?