A pigeon fancier, Richard, had an outbreak of paratyphoid among his birds. He lost 15 homing pigeons to the disease and managed to cure only 3 of 30 survivors. He noticed the rest have developed a odd symptom, they are twisting their heads. Richard wrote and asked if this was common.
If your birds are sick and you suspect paratyphoid, look for the neck twisting. It is a sure sign that what your racing pigeons are suffering from is in fact, paratyphoid.
Unfortunately, Richard, pigeons can't be cured of paratyphoid once they have it. Your best defense is to vaccinate your young birds while they are still in the nest. As long as you race your pigeons with other people's birds, you cannot prevent your birds from being exposed to the disease. Many people are not scrupulous about vaccinating their little ones.
You can clean your pigeon loft and disinfect it regularly, but it will have limited effect as long as the people with whom you race don't regularly disinfect their lofts as well.
The biggest problem is once a pigeon has paratyphoid disease, it will have it until it dies. They can also pass it on to other birds. The disease can remain dormant in a bird for a time but can be passed on to other birds via droppings. There are really only two ways to protect the rest of your pigeons if one is infected. You can either quarantine the infected bird, or you can cull it. It can be a hard decision to make and I don't enjoy making it, but those are the facts.
There are 28 diseases and 11 parasites that afflict pigeons.