Is a disease not only of our pigeons but Humans as well. It has been found in cats, dog, rabbits, rodents and many other species.
This protozoan will cause shortness of breath and, diarrhea. If you birds are showing signs of weight loss or if the pigeons appear anaemic toxoplasma may be the problem.
Treatment with antibiotics or sulphur based drugs will help.
You may want to have a vet confirm this is the problem and get the newest drugs to treat the problem.
Keeping it out of your loft will not be easy because it is believed biting insects are the mode of transmission.
If you can keep the problem down your pigeons will race faster on race day.