What... like... the remains of 10 hens? Buried in the litter?
If nothing else you've got some great compost material there. It might be a good idea to put the rest of the hens down as well. Respiratory infections in chickens are like cold sores. Once you've got the virus, it isn't going away, even if there are currently no symptoms.
How is the coop put together? You might be able to take off a few of the boards without having to remove too many layers of wood, and that would let a lot more air and light in.