It is not unusual for pigeons to develop one eye colds caused by Chlamydia. Symptoms include unilateral swelling of the membrane (conjunctiva) of the skin around the eye. The swelling of conjunctiva progresses to full blown infection with bulging of the eye membranes (skin around the eye). Eye infections may progress to infections of sinuses and lungs with pneumonia and death. Poor fertility or early death in babies in the egg or shortly after hatching may occur. Ornithosis is a true carrier of disease. Transmission is direct from pigeon to pigeon or via infected utensils or clothing. Prevention includes no new birds of any kind in the loft. Do not over crowd your pigeons and try to reduce stress of any kind. Use as much good ventilation as possible. In cases of confirmed Ornithosis, by a vet, 21 consecutive days of Doxycycline is a must. Be sure to use the proper dosage that should be on the container. Remove all grit during treatment and follow with a probiotic for three days.