Yersinia pestis (yellow bacteria with rod-like shape) is the causative agent of the systemic invasive infectious disease often referred to as the plague – or simply the ‘Black Death’. Y. pestis are Gram-negative and can infect humans and other animals. Human Y. pestis infection takes three main forms: pneumonic, septicemic, and the notorious bubonic plagues which has had devastating effects on the human population in Europe throughout history, killing over 75 million, in the 14th century.

The oriental Rat flea (Xenopsylla cheopis) is best known as the vector for the bacteria Yersinia pestis from rats to humans, and for spreading the resulting plague (black death) across Asia and Europe in the middle ages. In the 14th century (between 1347 and 1352), the disease killed 25 million in Europe and between 75 to 100 million worldwide, within five years. Today, the plague is still not wiped out completely and the WHO registers annually between 1’000-3’000 cases worldwide.

Credit: © Martin Oeggerli / Micronaut 2013, supported by Institute of Veterinary Bacteriology, University of Berne, Pathology, University Hospital Basel, School of Life Sciences, FHNW.