Greetings all! Six days ago, one of my 2-year-old Khaki Campbells appears to have picked up an upper respiratory infection. She had a low, hoarse quack. My chickens and ducks live together and we have never had problems, but I know that some illnesses that a duck can shake off easily may kill the chickens. So, removed her immediately and began a round of Tylan-50. She has been silent all week, but last night I finally heard her quack again. She still has a raspy, horse quack. She almost sounds like a drake. If my memory serves, it is a better sounding quack than 6 days ago, but it is still all wrong. Any ideas on how I should proceed? What might be ailing her? I'm clueless. Thanks.