Ornithosis is a bacterial infection of the respiratory tract caused by the Chlamydophila psittaci bacteria. This disease is one of the biggest wrongdoers in the pigeon sport. In general the Chlamydophila psittaci bacteria only causes an infection of the upper respiratory tract but in extreme cases it can also damage the internal organs (liver, lungs and spleen).
Direct contact with other contaminated pigeons (e.g. in the baskets) is the infection way by which the affection is being transmitted. There is also vertical transmission from parent to young through the egg. Ornithosis is more often present in poorly aired lofts (draught, bad ventilation, overpopulation).