One loft races certainly have problems with illness. This year the NCC in Ireland admitted to having a viral problem with several fatalities and, I believe , they involved a vet. When they started training returns were poor. However all credit to them for being transparent. The latest disaster (the Midlands National one loft race) with no birds in race time and this was into the second day certainly indicated that they had a problem especially when national returns were acceptable with only a 15 minute gap in liberation times. Several years ago Kenny Bald started a single loft at Edinburgh. He had big problems due to Circo Virus ( which attacks the immune system ) . I believe this turned the venture into a disaster and he closed down in the first year.