Ever since I was a toddler I have been drawn to animals. My Mum had to teach me at a very young age how to interact with dogs and horses without terrifying them, because she couldn't walk me past a dog on the street without me insisting on saying hello to it.
Not much has changed, I still feel the intense urge to say hello to every doggy I come across on a daily basis. I'm that annoying person making everyone watch an animal related video on Facebook, and secretly crying when the video shows them hurt/ abused or rescued.
I guess that pretty much sums up a passion for animals, which I believe is the most important thing you need when doing this kind of job. I will love your pet as if it were my own, and treat it and care for it exactly to your requirements and wishes. After all.... what's better than making new animal friends!!