Medieval and later-era plague suit, re-creation. Outfits of this type, worn by medieval physicians and made of cloth or leather, were uniquely associated with the plague in Europe. In addition to serving as a probable physical barrier to the plague pathogen, the suits had symbolic significance. The ability of birds to travel between earth and sky may have represented mediation between the earth and heaven. The costume's bird-like beak contained spices and vinegar-soaked cloth to mask the stench of death and decay and make the physicians' work less unbearable.

Bubonic plague could — with the right convergence of circumstances — re-emerge as a major threat. Its effects, however, might be less devastating. In the years since the Black Death, scientific knowledge of the pathogen and the mechanisms that are responsible for the plague has grown. Wearing distinctive garb as a protection against plague, medieval European physicians were unable to treat bubonic plague effectively or halt its spread, although they sought to contain the disease with quarantines and other basic health measures.

The microbe causing the disease was invisible and unknown until 1894, when Alexandre Yersin described it. Today, the bacterium known as Yersinia pestis is being studied at the level of individual genes and molecular functions, and the disease is being tracked at the global level. Accessible from anywhere in the world, computer networks contain information on Y. pestis, maps showing outbreaks, and sites containing genomic details of the Y. pestis microbe. While not currently in production, there is a vaccine against the plague, and targeted drug therapies are likely to be developed.

Left: Flea, Xenopsyllia cheopis (engorged with blood). In 1996, researchers identified three Y. pestis genes that may explain the intensity of the plague in the 14th century. These three genes in Y. pestis block an infected flea's ability to digest blood that it obtains from other animals. The genes help alter the site in the flea where Y. pestis colonizes, which in turn causes the flea to feed on, and infect, a new host. The net result is that fleas that carry Y. pestis and have these genes, go on a mad feeding frenzy — thus spreading plague more rapidly.
Right: Y. pestis, in a blood smear to which stain has been applied.