Or, how many germs can one dog BRING into a home? It seems like we go through up and down cycles of dogs coming into rescue with nasty upper respiratory infections, commonly called kennel cough. People who have fostered for a while know that this is the equivalent of the common cold for dogs and will, generally, run its course without any intervention. Sort of like a cold! In general, a by keeping the dogs separated vet will put a dog with kennel cough on a course of antibiotics to prevent any chance of the illness progressing into pneumonia (it happens, not frequently though!)
If your foster is coughing or has a runny nose when he arrives at your house it makes sense to do your best to try to isolate him until his cold has run it's course. I know this is easier said than done but remember the dog is in a better place in a crate at your house than he or she was in a shelter. If you are concerned that the dog seems to be getting worse or not improving after a few days please let me know. The rescue does have antibiotics available to send to you and we'll get them out to you as soon as possible.
Here's hoping that by keeping the dogs separated that the dogs that live in your home ALL the time will avoid the whole bug that's come in but if they don't we are more than willing to provide antibiotics for them too. (Don't forget this usually does go away on it's own without any intervention. Sort of like the saying "if you take cold medicine your cold will be gone in 7 days, if you don't it'll be gone in a week.") The antibiotics are primarily to keep it from progressing to something worse.
Less likely is that your foster will come to you with some type of parasite that could be passed along to your dog. If you keep your yard clear of waste that's less likely, the rescue does encourage you to get your foster in for a visit to the vet soon after their arrival so that any parasite load can be treated as soon as possible.
The last possibility that comes to mind is a dog with sarcoptic mange. There are two types of mange - demodectic is found frequently in puppies but also in dogs that have weakened immune systems due to stress, think how stressed your shelter dog is. . . but it is not contagious and does not make the dog uncomfortable, as in no itching, no redness, usually you'll see small bald patches appear on the dog. A quick skin scraping will confirm that the demodex mite, that is usually kept in check on a dogs skin by their natural immunities has multiplied and needs treatment, usually in the form of an ointment or injection. If it's a particularly stubborn case dips may be prescribed. Anything you can offer your dog to boost their immune system when they've been diagnosed with demodex will be a big help to them.
The other mange, the one you don't want to hear about is sarcoptic. Sarcoptic mange is contagious to both dogs and humans (in humans it's called scabies and the good news is that the mites cannot reproduce on humans so it's a short lived deal.) With dogs however it makes them itch and will spread to include hairloss, scabs and can, if left untreated, kill the dog. Sarcoptic mange is treated in much the same way demodectic is - ivermectin injections or dips. If you suspect your foster may have sarcoptic mange please keep him totally isolated from the other dogs in your home and limit your contact (especially hugging and cuddling) - the treatment is simple and fairly inexpensive. It's also, fortunately, not anywhere near as common as demodex. Please let me know if you are concerned your foster might have sarcoptic mange (believe me, if they have it, you'll know. . . ).
I'm sure there a lots of other things that could be traveling with your foster dogs but these are the big ones. I'm here to help all the foster homes (as is Kim as foster mentor) and all the other directors too! Ask any questions you have, let us know any concerns that you come across, we don't want you to wonder or worry - we want you to be comfortable with any dog we send you!