Plague on Purple

What am I looking at?

This is an image of Yersinia pestis bacteria on the so-called proventricular spines inside a flea’s mouth. The bacteria are the small yellow rods (1), and and the proventricular spines are in purple (2). Look closely for the rod-shaped bacteria because the debris and tissue surrounding the proventricular spines are also yellow (2).

Biology in the background

The bubonic plague, also known as the Black Death, has gained a terrifying reputation because there was an extensive outbreak of the disease in Europe and parts of Asia during the 14th century. In fact, it is estimated that the plague back then killed more than 25 million people – roughly two-thirds of the population of Europe at the time.

The plague is most often spread by a bite from an infected flea. The bacteria that cause the plague live on the mouthparts of fleas and thus enter the bloodstream of humans bitten by fleas. In the 14th century, the plague spread throughout Europe relatively quickly because infected fleas lived on rodents, which traveled on ships to new locations, bringing the fleas with them. In addition, since so little was known back then about how diseases are communicated, and many people lived in very close quarters, person-to-person infection was also a significant factor in the spread of the plague.

It is still present in the world, and there are occasionally small outbreaks around the globe. However, the disease is now easily treated with antibiotics and is rarely fatal when treated.

A Yersinia pestis bacterium can grow up to 3 micrometers long, or roughly 25 times smaller than the width of a human hair.

Technique

This image was created using colored scanning electron microscopy.