Corszya is a bacterial infection. The birds become carriers. Just like we can become carriers of strep or MRSA. We were exposed to it, had it, and it became part of our normal flora. It is no longer pathogenic (disease causing for us) but we can pass the bacteria to someone or something else who has no immunity and it becomes pathogenic or disease causing for them. Which can result in significant illness or death for them or they can fight if off too, survive and now become carriers....and on and on and on!!!!!!!!!!!!!!