Ive watched it for many years and here is what I think.Its a virus with many variants. It goes from ( MILD )not responding to a call to come in for a feed to ( FATAL )falling off the perch dead. Every loft has had it to a degree. Its like saying you have a classroom of kids and have never had any went down with a virus, this is complete nonsense imo. Some people say they haven't had it because they think it reflects on their own management, well this is nonsense as well as the virus cant be avoided im afraid. The best you can hope for is a very mild, short lasting dose of it.The last 2 years ive had it very mild, in fact 99% of fanciers probably wouldn't notice it because it was only a few retaining a very small bit of feed longer than usual. No other signs but I knew it was the YBS because it happens in my loft at around the same time every year. The Adeno VIRUS isn't the killer, its the secondary infection ( usually e coli or circovirus ) that does the damage.ps. If you get full blown Adenovirus then the birds need FIVE to SIX weeks to fully recover, although they start flying around the loft well after only a week, they are not ready for the stress of the race basket.omho