Is it possible that this bull could have been treated to clear up any infection ?
Most likely the answer is yes, but this also points to the UK farms policy of not vaccinating animals against things like this, and foot & mouth disease.
The reason given for this is that to test wether such diseases are present, the current testing system relies on isolating anitbodies to the particular disease.
The problem with this is that vaccinated animals would also show up as positive for the disease based on this method of testing.
It would make it very difficult to track the progression of the disease through to the source, but you could argue that vaccination would obviate the need to do so, as the disease could not spread anyway.
Other countries routinely vaccinate against many of this diseases because there is already a natural reservoir of the disease in those countries, so a large number of farm animals would be exposed anyway and carry the antibodies.
UK farmers blame badgers for carrying Brucellosis, a form of TB that can infect cattle and are unhappy about the current ban on badger killing.
It does strike me that there is some other politics involved here, maybe the bull could have been cured and a certificate issued, but that would then open up a chink in the current system of not vaccinating farm stock.
If you allow farm stock to be immunised, under our current situation, you would have to require this to be done, and enforce it, I doubt that the farming industry would want to pay for such costs.
The farming lobby is an extremely powerful grouping in the UK, this is likely true in most countries in Europe.