Is there any mold in the coop from wet bedding or wet feed? Aspergillosis can be a problem with fungal respiratory infection. Also, if the chick could have coccidiosis and be dying, there could be gasping. Have you seen the chick standing around puffed up, not eating, weakness with diarrhea or blood in poops, and ruffled feathers? Corid or amprollium is the treatment for coccidiosis.
If the problem is aspergillosis from mold, there is no treatment except to remove moldy conditions. If you suspect a bacterial respiratory disease such as MG, then Tylan 50 1/4 ml orally daily for 5 days may help. Here is a link to read about common diseases and symptoms: http://edis.ifas.ufl.edu/ps044