Plague is a disease that that has tormented mankind for centuries. The Byzantine Empire experienced a large epidemic in the sixth century, and the Black Death killed millions of people throughout Europe in the fourteenth century. Today the United States averages approximately 13 cases of plague each year with a 15% fatality rate.
Plague is caused by the gram-negative bacteria, Yersinia pestis. The host for this bacteria is the rodent. In years past the most commonly involved rodent was the rat, but in the United States animals most commonly involved include ground squirrels, rock squirrels, and prairie dogs.
The Yersinia pestis bacteria is spread from rodents to humans by fleas, although it is possible for transmission to occur by infectious aerosol. A bite from an infected flea causes an infection in the lymphatic system leading to bubonic plague, the most common form of plague. Inhalation of the aerosolized bacteria results in a pulmonary infection known as pneumonic plague.
Plague as a Weapon
The Yersinia pestis bacteria is easily destroyed by drying, heat, and ultraviolet light making direct weaponization difficult. During World War II the Japanese bred infected fleas by the billions and released them over northern Chinese cities causing numerous epidemics. Plague has been endemic in those areas ever since. In the past, the United States dismissed plague as a potential bioterror threat because the disease persists in the area and could cause casualties on both sides long after an attack. However, reports that the former Soviet Union's biological warfare program developed a dry, antibiotic-resistant, environmentally stable form of the plague organism has led the Centers for Disease Control and Prevention (CDC) to categorize plague as a Category A agent.
Bubonic Plague Symptoms
Bubonic plague is acquired as the bacteria is transmitted from flea to human through a flea-bite. The incubation period of bubonic plague is 2 to 6 days. The first symptoms of bubonic plague are the sudden onset of headache, fatigue, muscle pains, and fever. Six to eight hours later the lymph nodes in the armpits or groin become markedly enlarged and exquisitely painful. These tender, enlarged lymph nodes are called buboes. Bubonic plague has a 60% mortality rate if not treated.
Bubonic Plague Pictures
Pneumonic Plague Symptoms
Pneumonic plague is acquired by breathing aerosolized bacteria from a bioweapon or respiratory droplets from an infected person. The incubation period is 1 to 3 days leading to the sudden onset of fatigue, fever, muscle aches, and cough. The pneumonia progresses rapidly to shortness of breath, cyanosis, and coughing blood. People with pneumonic plague do not develop buboes. Pneumonic plague has a 100% mortality rate if not treated.
Both bubonic plague and pneumonic plague can develop into septicemic plague if the bacteria reach the bloodstream. This very serious blood infection results in shock and death in 100% of cases if not treated.
Treatment of Plague
All forms of plague are treated with antibiotics, although some antibiotic-resistant strains have been reported. The most commonly used antibiotics are gentamicin, tetracycline, sulfonamides, or chloramphenicol. People who have been exposed to infected fleas or who have been within 2 meters of a coughing patient with pneumonic plague should be treated with antibiotics before they develop symptoms. A vaccine of killed Yersinia pestis was available for high risk individuals, but this product was discontinued by its manufacturers in 1999 and is no longer available. The vaccine was never approved for general use in the United States.