My DIL's Mom was having problems with their older GSD. She is okay, now, but they think it was because of the recalled Glucosamine tablets they have been using for years. Personally, I didn't realize NON FOOD items (such as ear cleaner) could pass on salmonella.
http://www.fda.gov/Safety/Recalls/ucm217999.htm
The list is too long to post, but there are some odd things on there that you might be using...so check it out.