Plague

Bubonic plague was a scourge of Europe in the Middle Ages, when it is estimated to have killed one-fourth to one-third of that continent's population. The disease is caused by the bacterium Yersinia pestis, which is transmitted to people mainly through the bite of a flea. People with lung plague can also spread the bacterium directly to others. The microbe normally infects rodents, which serve as the primary carriers for the disease. Today plague continues to affect up to 3,000 people each year worldwide. In the United States the bacterium primarily infects prairie dogs and other rodents of the southwest, with few human cases occurring each year. In 1999, nine cases of plague in people were reported to the CDC. ¹

After an infective flea bites a person, the bacteria migrate to the nearest lymph nodes, where they can cause a painful swelling or bubo, from which bubonic plague takes its name. The bacteria quickly spread throughout the body and can cause death within 2 to 4 days of the onset symptoms. In some cases, the bacteria infect the lungs and cause pneumonic plague, a deadly and highly contagious form of the disease.

Under most circumstances, plague can be successfully treated with antibiotics. No vaccine is available.

Studying the Relationship between Bacterium and Flea

Tom Schwan, Ph.D., and Joseph Hinnebusch, Ph.D., from NIAID's Rocky Mountain Laboratories investigate how Y. pestis infects the digestive tract of its flea host and how the bacterium is transferred to humans. By understanding molecular mechanisms of flea-borne transmission, they hope to gain insight into new ways to break the infection cycle.

Unraveling Yersinia Biology

Susan Straley, Ph.D. and Robert Perry, Ph.D., of the University of Kentucky, and Gregory Plano, Ph.D., of the University of Miami study disease-causing proteins and genes of Y. pestis and how these proteins are regulated by the bacteria. Understanding the molecules required for Y. pestis to function may allow researchers to devise new approaches to destroying the bacterium. Drs. Straley and Perry study proteins that function in the lung during pneumonic plague. These studies will enhance our understanding of the how Y. pestis infects the lungs and how researchers might best protect people against possible bioterrorism based on Y. pestis.

Dr. Perry also investigates how Y. pestis diverts and acquires iron from the host that is essential for growth of the bacterium. In addition, he examines genes of Y. pestis that are vital in transmitting the disease from fleas to mammals. Understanding the molecular mechanisms behind both iron uptake and disease transmission may generate new therapeutic strategies.

Deciphering the Genetic Code

As part of a program to determine the genetic blueprints of several closely-related bacteria, Frederick Blattner, Ph.D. , from the University of Wisconsin is determining the DNA sequence of Y. pestis. This information should provide clues to the inner workings of the bacterium and potential vaccine or drug targets.

Additional Links

World Health Organization information on plague

CDC information on plague

1. Centers for Disease Control and Prevention. Summary of Notifiable Diseases, United States, 1999. Morbidity and Mortality Weekly Report 2001;48:1-104.