Hygiene and Birds (including Great Tits)
According to the BBC NEWS website (today, 22.11.2012 in the Environment section), our garden birds are being affected by an avian pox that leaves the creatures with swollen lesions.
Spread from bird to bird (originally from insects coming to the UK), it is advised that WE can HELP by cleaning bird feeders, boxes (check for tenants first!) and bird-baths with soapy-water. It may help.