What is plague? Plague is a disease caused by Yersinia pestis (Y. pestis), a
bacterium found in rodents and their fleas in many areas around the world.
Why are we concerned about pneumonic plague as a
bioweapon? Yersinia pestis used in an aerosol attack could cause cases of the
pneumonic form of plague. One to six days after becoming infected with the
bacteria, people would develop pneumonic plague. Once people have the disease,
the bacteria can spread to others who have close contact with them. Because of
the delay between being exposed to the bacteria and becoming sick, people could
travel over a large area before becoming contagious and possibly infecting
others. Controlling the disease would then be more difficult. A bioweapon
carrying Y. pestis is possible because the bacterium occurs in nature
and could be isolated and grown in quantity in a laboratory. Even so,
manufacturing an effective weapon using Y. pestis would require advanced
knowledge and technology.
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Is pneumonic plague different from bubonic plague? Yes. Both are caused by Yersinia pestis, but they are transmitted
differently and their symptoms differ. Pneumonic plague can be transmitted from
person to person; bubonic plague cannot. Pneumonic plague affects the lungs and
is transmitted when a person breathes in Y. pestis particles in the air.
Bubonic plague is transmitted through the bite of an infected flea or exposure
to infected material through a break in the skin. Symptoms include swollen,
tender lymph glands called buboes. Buboes are not present in pneumonic plague.
If bubonic plague is not treated, however, the bacteria can spread through the
bloodstream and infect the lungs, causing a secondary case of pneumonic
What are the signs and symptoms of pneumonic plague? Patients usually have fever, weakness, and rapidly developing pneumonia
with shortness of breath, chest pain, cough, and sometimes bloody or watery
sputum. Nausea, vomiting, and abdominal pain may also occur. Without early
treatment, pneumonic plague usually leads to respiratory failure, shock, and
How do people become infected with pneumonic plague? Pneumonic plague occurs when Yersinia pestis infects the lungs.
Transmission can take place if someone breathes in Y. pestis particles,
which could happen in an aerosol release during a bioterrorism attack.
Pneumonic plague is also transmitted by breathing in Y. pestis suspended
in respiratory droplets from a person (or animal) with pneumonic plague.
Respiratory droplets are spread most readily by coughing or sneezing. Becoming
infected in this way usually requires direct and close (within six feet)
contact with the ill person or animal. Pneumonic plague may also occur if a
person with bubonic or septicemic plague is untreated and the bacteria spread
to the lungs.
Does plague occur naturally? Yes. The World Health Organization reports 1,000 to 3,000 cases of plague
worldwide every year. An average of five to 15 cases occur each year in the
western United States. These cases are usually scattered and occur in rural to
semi-rural areas. Most cases are of the bubonic form of the disease. Naturally
occurring pneumonic plague is uncommon, although small outbreaks do occur. Both
types of plague are readily controlled by standard public health response