The correct option is A Yersinia pestis
In 1000AD, a bacteria called Yersinia pestis caused the bubonic plague. It was transmitted by an infected flea. Infected people showed common symptoms like buboes, chills, nausea, fever, seizures, etc. It affected the lymphatic system. The lymph nodes turned black and swell post infection. This is why, this disease was termed black dealth. As the causative reasons were unknown and there was a lag in the treatment and became a global epidemic. It caused a huge dip in the world population.