For the sake of discussion let's just say this virus makes people more prone to Obesity (certainly there is a lot of correlation)... It would be interesting to test if the damage and/or mechanism of this virus is a one time event or ongoing issue. What would happen if the people and/or chickens were given anti-viral meds... or took lots of vitamin C? Is the effect reversed? I have no idea what would happen but I'd be very interested to see. HIV patients given antiviral drugs sometimes experience lipodystrophy, which may somehow be related but that's just a wild guess.

Also, if I'm a ruthless chicken farmer wouldn't I want all my chickens to have this since it makes them heavier based on the same food intake?

Finally, what's going on with the people who have the antibody but haven't gained weight? What's different about their immune function, diet and/or lifestyle.