The plague is called by a bacterium called Yersinia pestis which is still around so yes it could spread again and there are even a few cases a year!
However, if identified (doctors wouldn’t typically assume illness was the plague), then it’s easily treatable!
The worry is that it develops resistance to the antibiotics that, in modern times, easily kill it! Another worry is that of bioterrorism, if it was engineered to be drug resistant and spread around.
One of the earliest documented uses of bioweapons was in 1340 as dead horses and people infected with plague were flung over the castle walls in Crimea. This is thought to have furthered the second major outbreak in Europe!
The plague was caused by a huge growth in the number of black rats living close to man. Infection was spread to man through bites from rat fleasThese rats were infected with a bacterium called Yersinia pestis, which still exists today and actually caused 108 deaths in 1992.
However, if the plague was re-introduced into the UK, it is now treatable as we have antibiotics. Also there is now a vaccine against the plague.
However, very common infections that we consider minor, like bladder infections, could soon become killers if the bacteria become resistant to our antibiotics. This has already started to happen and scientists are currently developing new ways to try and treat bacterial infections.