I wouldn't worry about parasites if you feed human quality food. If you feed wild game like rabbit or deer and are concerned, freeze it for a few weeks. Bacteria is also very little risk- more of a risk for you if you don't clean up good. Dogs have very strong digestion and it can kill a lot of stuff- after all, they are known to eat poop and stinky stuff out of the garbage and that rarely does anything to them.
We have 3 dogs on a full raw diet including our Pug. I was concerned about him being able to handle the bones with his short jaw but he does just fine and he's fit as a fiddle. I don't see why a Shih Tzu couldn't do well on this diet.
If you want to go full raw the best thing to do is to just switch them right over. Start with chicken - most likely wings and necks for little guys like yours. Keep them on nothing but chicken for 2 weeks or so to let them adjust. Mine had the runs for a day or so then they were back to normal. After 2 weeks you can gradually start introducing 1 new food at a time, and observe how they react to it. For example, introduce boneless pork or ground turkey as muscle meat. After another week, try something else. Eventually you should get to a ratio of about 65% raw meaty bones (chicken necks, wings, legs, backs and beef short ribs or pork ribs are a good place to start), and 35% muscle meat- boneless pork, chicken breast, beef, turkey, beef heart, etc. You also want to supplement them with some organ meat such as liver as this has some nutrients they can't get elsewhere. Only a small amount is needed- maybe an ounce a day or every other day for a little dog. You can also feed whole raw eggs, shell and all. I give mine an egg every other day. For adult dogs that are mostly house pets (not working etc) you should target about 2% of their bodyweight per day, split into the 65/35 ratio. So if your dog is 15lbs, you'd need about 5-6 ounces of food per day.
Here is a link to a site that has a nice spreadsheet that will help you calculate your dogs needs and give you a way to help them diet or gain weight if needed.
http://www.rawdogranch.com/index.html
I've been doing this for 6 months or so now, and find the preparation time is minimal. I take out several days worth of food at a time, and it takes maybe 10 minutes to weigh out the portions for each dog. After a while you get pretty good at eyeballing it. If I'm feeding a muscle meat like boneless pork, I cube it up so they don't try and swallow a huge hunk of it, but everything else is fed whole. If I'm feeding the pug a chicken drumstick, I do remove the bone as he has a tendency to try and swallow to big of a piece. I still give him the bone but without the meat, he will crunch the bone better. I get my chicken by the case but it's in individual packages inside the case so I take a package at a time out. When I get something like pork on sale in a large hunk, I'll split that into smaller hunks and then take one out and use it til it's gone. We look for things on sale a lot and if there is a good deal, stock up. I try to keep the cost at about $1 per lb total. Since the chicken legs are cheap, if I spend a little more on ground beef or turkey or some other boneless meat, it all works out in the end. I've been tracking my expenses since Sept, and find I'm spending about $100 per month on 3 dogs that are 80+lbs, 65lbs, and 25lbs.
