Bird-bird transmission (EDIT: oops, of H5N1) is EXTREMELY easy and requires pretty extreme quarantine protocols. If you track bird shit on your shoes, other birds can catch it from that for like a month unless it is properly cleaned and sanitized. (Source: have friends who work for wildlife rescue organizations that include birds.)
Might be something like that? Or just a long incubation period?
Bird-bird transmission (EDIT: oops, of H5N1) is EXTREMELY easy and requires pretty extreme quarantine protocols. If you track bird shit on your shoes, other birds can catch it from that for like a month unless it is properly cleaned and sanitized. (Source: have friends who work for wildlife rescue organizations that include birds.)
Might be something like that? Or just a long incubation period?