I have an adult hen, at least 3 years old, who has been having increasingly worse respiratory distress for several days. - I noticed her mouth gaping open when she breathed but she was otherwise behaving normally. No visible evidence of gapeworm so I treated with Duramycin-10 which she has been on for 3 days (dissolved in her water which she is drinking ample amounts of). - She seemed to get better and started vocalizing again, but her voice was hoarse. I came home today and she was gaping again so I bathed her and examined her. - No sign of external mites in her or any of my other chickens but I noticed that after her bath and being handled her breathing was much worse. - Her tail is bobbing, her breathing is audible. - She has no nasal crust, swelling or discharge - She has no eye symptoms - She is not coughing or sneezing - I cannot see anything in her mouth/throat. - Her appetite is good and her poop is normal. I am leaning toward the diagosis of air sac mites. I have injectible ivermectin on hand and am not sure if that is appropriate treatment or if it is how to administer it. Please advise.