THANKS FOR ALL THE ADVISE AND TAKING TIME TO WRITE
....And AireScottie is right. I am sure your friend feels for all her animals, but there is something a little wrong with her I think. It is not good for them to be kept like this. To let numerous dogs die of Parvo, for a start, and not to get them all vaccinated, is irresponsible dog-ownership. I'm sorry to have to say that because I am sure she is very attached to them, but something needs to be done.
This is a scenario that has often presented itself to me in the past!!
I have cleaned up peoples' houses where you wouldn't even let a rat go!
It's noble of you to consider this. If you wore gloves, a dust-mask, and showered afterwards YOU would probably be fine.
But the risk is too great for your dog. Parvo virus can remain on surfaces, even outside dirt in the yard, for a very long time. I would say you have to explain this to your friend. Let's hope she understands. Don't do it.
I'm sure you would hate to rat out your friend, but this sounds like a case where you need to call the local Humane Society or animal control; you can call anonimously. Your friend can't properly take care of all those animals. It's very unfair for the animals to have to live in conditions like that. And yes, you could catch something which you bring home to your dogs. The dogs could have worms and any number of other things that could make your dog very ill.