Welcome to YT!!!!

on your new baby!!!!
You will need to let them meet, but stay with them.
It will take time for your Shih Tzu to adjust to a new
furbaby, but they will soon be friends.
About Parvo,
just make very sure you don't let the new baby touch the ground outside
before he/she has all their shots. When we get a new furbaby, I make people step in a pan of bleach before they come in my home. And I don't take them out side on any ground for two weeks after the last shot.
It is much better to be safe.
Good luck to you, please post pictures of your furbabies, we would love to see them.
And again Welcome to YT