Vent Gleet

Vent gleet is essentially an inflammation of the cloaca, another name for a hen’s vent. It present similarly to thrush and is caused by Candida albicans, though it can also be linked to the herpes virus. 

https://www.bhwt.org.uk/blog/health-welfare/everything-you-need-to-know-about-vent-gleet/#:~:text=If%20you've%20noticed%20a,unpleasant%20–%20we%20did%20warn%20you!