Paratyphoid is just about the worse thing that can hit a flock of pigeons. Whilst I dont advocate vaccinating against this I would advise anyone that have brought several pigeons in to give them a 14 day course of treatment against it, especially if they've been bought in from more than one loft. A negative result from a droppings test doesn't guarantee your pigeons a free from paratyphoid, each individual pigeons has to be tested several times as they dont always pass the bacteria in their droppings. No pigeon is immune to worms so I would advice treating against these. Canker: some treat some dont, I'm one of those that dont.