Worldwide, approximately 1,000 to 3,000 cases of plague occur each year. This infectious disease is far less common than it once was, due to improvements in living conditions, better sanitation, and the introduction of antibiotics. Plague is caused by Yersinia pestis bacteria, which can generally be transmitted in one of three ways:
- Bites from infected rodent fleas
- Direct contact with infected tissue or bodily fluids
- Inhaling infected droplets.
The particular symptoms a person experiences will depend on the type of plague they have (bubonic, septicemic, or pneumonic). For example, a person with bubonic plague may develop tender, enlarged lymph nodes (buboes). A person with pneumonic plague -- the most serious form of the illness -- may eventually go into respiratory failure. Even with appropriate treatment, the mortality rate for pneumonic plague is 75 percent.
(For more details about this disease, including a discussion on plague-related bioterrorism, click Plague.)