History of Plague
The history of plague has had a huge impact on society for centuries. Numerous references in art, literature, and monuments attest to the horrors and devastation of past plague epidemics. The history of plague research includes the fundamental but separate works by Yersin and Kitasato, in 1894, on the discovery of plague's connection with rats, as well as Simond's research in 1898 on transmission methods.
Plague has a remarkable place in history. For centuries, plague represented disaster for those living in Asia, Africa, and Europe, where, it has been said, populations were so affected that sometimes there were not enough people left alive to bury the dead.
Since the cause of plague was unknown, plague outbreaks contributed to massive panic in cities and countries where it appeared. The disease was believed to be delivered upon the people by the displeasure of the gods, by other supernatural powers, or by heavenly disturbances. Innocent groups of people were blamed for spreading plague and were persecuted by the panicked masses.
Numerous references in art, literature, and monuments attest to the horrors and devastation of past plague epidemics. So imprinted in our minds is the fear of plague that, even now, in the 21st century, a suspected plague outbreak can incite mass panic and bring much of the world's economy to a temporary standstill. The number of human plague infections is low when compared to diseases caused by other agents, yet plague invokes an intense, irrational fear, disproportionate to its transmission potential in the post-antibiotic/vaccination era.
The fundamental but separate works by Yersin and Kitasato, in 1894, on the discovery of the etiologic (disease-causing) agent of plague in Hong Kong, opened the way for investigating the disease and how it is spread. Kitasato and Yersin described, within days of each other's findings, the presence of bipolar staining organisms in the swollen lymph node (bubo), blood, lungs, liver, and spleen of dead patients. Cultures isolated from patient specimens were inoculated (injected) into a variety of laboratory animals, including mice. These animals died within days after injection, and the same bacilli (disease-producing bacteria) as those found in patient specimens were present in the animals' organs.
Though both investigators reported their findings, there were a series of confusing and contradictory statements by Kitasato that eventually led to the acceptance of Yersin as the primary discoverer of the organism, now named after him, Yersinia pestis. Yersin had recorded that rats were affected by plague not only during plague epidemics, but also often preceding such epidemics in humans. In fact, plague was designated, in local languages, as a disease of the rats. Villagers in China, India, and Formosa (Taiwan) described that when hundreds and thousands of rats lie dead, in and out of houses, plague outbreaks in people soon followed.
The transmission of plague was described by Simond in 1898. He noted that people who became ill did not have to be in close contact with another person who had plague to acquire the disease. In Yunnan, China, inhabitants would run away from their homes as soon as they saw dead rats. On the island of Formosa, residents considered handling dead rats a risk for developing plague. These observations led Simond to suspect that the fleas might be an intermediary factor in plague transmission, since people acquired plague only if they were in contact with recently dead rats, and were not affected if they touched rats that were dead for more than 24 hours. Simond demonstrated that the rat flea (Xenopsylla cheopis) transmitted the disease in a now-classic experiment in which a healthy rat, separated from direct contact with a recently plague-killed rat, died of plague after the infected fleas jumped from the first rat to the second.