Plague Disease: Causes, Forms, Symptoms, and Treatment

Understanding Plague: Causes, Forms, and Treatment

The Gram-negative bacterium Yersinia pestis is the causative agent of the systemic invasive infectious disease known as plague.

Historical Impact of Yersinia pestis

• Yersinia pestis has been responsible for three devastating pandemics: the Justinian Plague, the Black Death, and modern plague.
• The Black Death, in the 14th century, is estimated to have reduced the total world population from 450 million down to 350–375 million.

Transmission and Symptoms

Yersinia pestis is primarily a rodent pathogen, with humans being an accidental host. Infection typically occurs when a human is bitten by an infected rat flea. The flea draws viable Y. pestis organisms into its intestinal tract, where they multiply.

When the bacteria travel to the bloodstream, it causes blackening and death of tissue (or gangrene) in extremities, most commonly the fingers, toes, and nose.

Mortality Rates

Historically, without treatment, the host would often die from the plague. With the advent of antibiotics, the mortality rate can be significantly lowered to just 16%.

Forms of Plague

Bubonic Plague

The most common form of plague, bubonic plague, is usually contracted when an infected rodent or flea bites you. In very rare cases, the bacteria can be acquired from material that has come into contact with an infected person.

Bubonic plague infects the lymphatic system (part of the immune system), causing inflammation. Untreated, it can progress into the blood, leading to septicemic plague, or to the lungs, causing pneumonic plague.

Septicemic Plague

When the bacteria directly enter and multiply in the bloodstream, it is known as septicemic plague. Both untreated bubonic and pneumonic plague can lead to septicemic plague.

Pneumonic Plague

When the bacteria spread to the lungs, it results in pneumonic plague — the most lethal form of the disease. This form is highly contagious: when someone with pneumonic plague coughs, the bacteria from their lungs are expelled into the air. Other people who breathe that air can also develop this form, which can lead to an epidemic. Pneumonic plague is the only form of plague that can be transmitted from person to person.

Prevention and Treatment

Historically, quarantine was a key measure, entailing staying out of the path of infected individuals, rats, and fleas. The uninfected would typically remain in their homes and only leave when necessary.

All forms of plague can be treated with the proper antibiotics. However, plague can be deadly if no antibiotics are taken or if treatment is delayed.