I wrote this a couple years ago, I should add a couple things, but this will get you pointed in the right direction. Best wishes James Gratz.

This is not a simple disease but a complex of things. Chalamydia, Mycoplasma and herpes virus all can be involved together or separately. Other bugs can also play a role from time to time. One eye cold is a separate disease which usually responds to ointment in the eye.

Chlamydia causes ornithosis a disease of parrot type birds and also can spread to people. Ornithosis can cause severe disease in young pigeons just out of the nest. Typical signs are depression, mild to severe respiratory signs, diarrhea, total lack of food intake, and a striking increase in water intake. The birds die after 1-2 weeks if untreated. This form of the disease is a septicemia, and infection that has spread throughout the body. Chlamydia multiplies in the internal organs causing the liver and spleen to be greatly enlarged at necropsy. The second form of the disease is a chronic infection that can be life long. The bird can look healthy but relapse under stress. These carriers can serve as a source of infection. In ornithosis both the eye and nostril will be infected having a watery to mucus drainage. Spread occurs in water fountains, through direct contact, and by inhaling infected dust. Fecal material can be infective for several weeks.

Mycoplasma is the second disease in this group and is also common. Different types of Mycoplasma affect all types of birds and animals. It tends to be specific and not spread between species. Most pigeons have been infected with Mycoplasma. Stress of some type can turn this hidden infection into an outbreak. Mycoplasma does not cause a discharge from the eye. Only a nasal discharge is observed. A rattle or wheeze is often noticed as well, especially at night. Death is unlikely unless Mycoplasma opens up the door for other diseases. Spread is much the same as for Chalamydia. Mycoplasma is probably impossible. Good health will keep it at a low level. In other species a vaccine is available, but I wouldn't expect it to work unless it was made specifically for pigeons.

Herpes virus and other viruses can spread rapidly from bird to bird causing an irritation of the respiratory tract and giving one or both of the above the opportunity to get started. The only weapon we have here it to keep new or returning birds isolated for a time. Ideally 4-6 weeks. This is a good idea for many diseases, but impractical for racing birds.