I've read that it has high mortality and very contagious.
I think, from my experience in medical and the articles we've read, it quickly went into septic shock. Gasping, limp, seizure like episodes. Refusing to eat or drink. It was definitely dying. I didn't think it would recover. This duckling is a fighter. I gave him a 0.1 ml shot in his thigh once daily since Sunday, and also sulfamethoxazole solution with niacin in water. Sunday I forced liquids in his throat between gasps. Also some food mush with electrolyte water. I kept him in a hoodie I wore backwards to keep him with me at all times. He started eating mush Monday on his own, and water. The only symptom now (5 days later) is it has almost no balance. I say almost because it had zero up until this morning. He was flat on his back flapping his legs, unable to get his feet under him. But it's getting it's feet back under him today. He's eating, drinking, breathing normally, active, talkative. I'm hopeful he will make a full recovery. He's a silver appleyard from Johnson's. We ordered three. Another one started showing symptoms and I gave it antibiotics immediately. It is not showing symptoms now. I am thinking the batch of appleyards were exposed to the bacteria at the hatchery. No other ducklings we ordered have symptoms. But I gave them all the sulfamethoxazole solution since then. The rest are perfect.