While all plague is bad, the bubonic syndrome is the least worst. From there it can go into the blood (septicemic) and from there it can get into a lung (pneumonic), after which the patient can spread an aerosol of the bacteria. That can spread from person to person like wildfire, and is of course very very lethal.

Back when I was playing the biology game, there were stories of e.g. a researcher opening a flack of salmonella that he didn't realize was under pressure, breathing in an aerosol of it, and dying before his doctors realized what was going on.

This is why anthrax as a weapon is so bad (although hard to spread), so much lung tissue gets exposed, there's a lot of surface area, so there's a quick and all too soon massive infection. Use a bactericidal antibiotic too late and all the toxins in the bacterial are released when they blow up, which will kill the patient. The window to diagnose and successfully treat pulmonary anthrax is measured in hours, as I recall, an Air Force flight surgeon's manual said something to the effect that "the first sign a patient has pulmonary anthrax is his sudden death".

Cat bites alone can be pretty bad. I had a neighbor who had a cat bite and ended up having to wear an IV tube at home and go into the doctor's office for his daily IV antibiotics for a week.