If you lose another chicken, do some research beforehand to find out where you might get testing or a necropsy. They can confirm MG or whatever disease is happening. MG can be passed through the hatching eggs, but not other respiratory diseases. Most make the whole flock carriers for life, but once all birds are gone for several weeks, healthy baby chicks can be purchased from a hatchery to start over. Here is a link you can contact to see if they do necropsies or testing for common respiratory diseases:
https://www.gov.mb.ca/agriculture/a...th/poultry-flock-avian-influenza-program.html
https://www.gov.mb.ca/agriculture/a...th/poultry-flock-avian-influenza-program.html