If your flock was heavily infested you will see such symptoms after a large die-off. Chickens will develop respiratory symptoms that may resolve on their own or require further treatment. If your chickens were already harboring a respiratory infection, the added burden of dead tissue bombarding their lungs and air sacs can cause illness. Unfortunately, scar tissue can form and, while symptoms may improve, the chicken may never be 'normal'. Observe your flock closely and if they remain alert, active, and eating well, do nothing. However, if they are not doing well you can consult a veterinarian who may suggest the appropriate antibiotic.