Plague - Yersinia pestis
Yersinia pestis, the bacterium that causes plague, poses as great a threat to human life now as it did during the 14th-century Black Death plague pandemic. The major threat these days is not through natural transmission of plague - but through intentional transmission, by terrorists.
Infected fleas usually transmit Y. pestis just among rodents. When a plague outbreak among rodents kills many of them at once, infected fleas that were feeding on the rodents' blood jump to other animals and humans, carrying the infection with them.
During the Black Death, plague caused 20 million to 30 million deaths in Europe. More recent pandemics through the late 19th century also killed millions of people worldwide. Improved living conditions and health services throughout the world have made such large-scale outbreaks of natural plague unlikely, but small plague outbreaks continue.
These days, human weapons are much more likely than rats to cause a plague pandemic. Plague is considered one of the most dangerous agents of biological warfare. The threat would come through pneumonic plague - the least common form of naturally occurring plague. Terrorists might be able to convert plague into this form, which could be sprayed through the air and infect anyone who might inhale the plague bacteria.
No plague vaccines are currently available, but antibiotics can effectively treat plague in the majority of cases when started very early.
Signs and symptoms
Three types of plague occur: bubonic, septicemic and pneumonic. Symptoms of plague vary depending on the type and on how you contract it. It's possible to develop more than one type of plague.
This is the most common type of plague in humans, accounting for more than 80 percent of U.S. cases from 1947 to 1996. Bubonic plague is caused by a bite from an infected flea and characterized by an enlarged, infected lymph node called a bubo.
Symptoms of bubonic plague generally appear within 2 to 6 days after a plague-infected flea bites you. After you're bitten, the bacteria travel through your lymphatic system, inflaming the first lymph node they reach. The resulting bubo is usually 1 to 10 centimeters in diameter, swollen, painful and warm to the touch. It can cause so much pain that you can't move the affected part of your body. The bubo usually develops in your groin, but may also appear in your armpit or neck, depending on where the flea bit you. More than one bubo can develop, but typically buboes affect only one area of your body.
Buboes may not be noticeable until a day or more after other symptoms appear. Other symptoms of bubonic plague include:
Without treatment, this type of plague may cause death within 4 to 6 days.
You can contract this form of plague when a fleabite results in bacteria directly entering your bloodstream, or when bacteria in your body from another type of plague spread to your bloodstream. A bubo may accompany septicemic plague if it occurs as secondary to bubonic plague.
Signs and symptoms of septicemic plague include:
The gangrene associated with septicemic plague inspired the nickname Black Death for the 14th-century pandemic. Without treatment, death occurs rapidly — often within 1 to 3 days.
Pneumonic plague is the least common form of plague. Primary pneumonic plague can occur when you inhale infectious droplets coughed into the air by a person or animal with pneumonic plague. Early symptoms, which occur within 1 day to 4 days of inhaling contaminated droplets, include:
You can also develop secondary pneumonic plague when bacteria from one of the other two types of plague spread to your lungs. About 12 percent of people with bubonic or septicemic plague develop secondary pneumonic plague.
Pneumonic plague progresses rapidly and may cause respiratory failure and shock within 2 days of infection. Most infected people die if they don't receive antibiotics within a day after symptoms first appear.
Plague resulting from a bioterrorist attack
Plague bacteria can be turned into an aerosol and spread over large populations with bioterrorist weapons. An attack of this kind would cause pneumonic plague — the most deadly and most contagious type. In 1970, the World Health Organization estimated that if plague bacteria were sprayed over a city of 5 million people, up to 150,000 people could be infected and 36,000 might die.
The incubation period for pneumonic plague symptoms following a bioterrorist attack is more variable than in naturally occurring infection, lasting from 1 to 6 days. Symptoms mirror those of naturally occurring pneumonic plague, but may also include nausea, vomiting, abdominal pain and diarrhea.
Other signs that a bioterrorist event or germ warfare is behind a pneumonic plague outbreak include a high incidence of pneumonic plague in humans in regions of the country that haven't had outbreaks among animals or rodents, or when plague occurs in people without any known risk factors.
Related Sites: Bacterial