You cannot see gapeworms without dissecting the trachea (airway) when doing a necropsy. A vet can do a fecal float though, and see the worm larvae in the droppings under a microscope.
I have dealt with infectious bronchitis. Mine only had sneezing and a little dirt around nostrils, and it lasts about 4 weeks. MG will cause the eye bubbles/foam, and more symptoms such as wheezing, gasping, and rales/crackles. Zoologix lab in TX will do PCR testing for 8 respiratory diseases by having you collect the swabs on a sick bird with symptoms at home for around $40-50. They are private, and here is a link:
https://www.zoologix.com/avian/Datasheets/PoultryRespiratoryPanel.htm
I have dealt with infectious bronchitis. Mine only had sneezing and a little dirt around nostrils, and it lasts about 4 weeks. MG will cause the eye bubbles/foam, and more symptoms such as wheezing, gasping, and rales/crackles. Zoologix lab in TX will do PCR testing for 8 respiratory diseases by having you collect the swabs on a sick bird with symptoms at home for around $40-50. They are private, and here is a link:
https://www.zoologix.com/avian/Datasheets/PoultryRespiratoryPanel.htm