- Scientific name: Yersinia pestis; a bacterium (not a virus)
- Plague is the disease that develops after infection with this bacterium.
- Humans contract plague by inhaling it or from the bite of an infected flea.
- Plague infection takes three primary forms:
- Only pneumonic plague is contagious through respiratory droplets with direct close contact (within 6 feet).
- Plague is highly lethal if untreated.
- Plague can be treated with antibiotics if caught early.
- Some plague infections occur naturally each year (usually bubonic).
Plague as a Weapon
Because pneumonic plague is highly lethal and contagious and would quickly overwhelm communities and their healthcare systems, countries with biological weapons programs have explored using plague in aerosol form to infect large groups of people.
- A pneumonic plague outbreak would be difficult to contain.
- Treatment must be immediate (within 24 hours of first symptoms) to be successful.
- Once refined, plague bacteria can be released into the air undetected.
- Once released into the air, plague bacteria remain infectious for up to an hour.
- Aerosolized plague bacteria can infect large groups of people quickly.
- Plague bacteria degrade quickly in sunlight or heat.
What We Don't Know About Plague as a Weapon
Experts are uncertain as to how wide an area would be affected by an aerosol release of plague bacteria or whether it can be disseminated successfully through the mail, as was the case with anthrax.
Identifying an Attack
A plague attack will most likely go unnoticed until people exhibit symptoms.
Tests of powder or residue can identify the presence of plague bacteria.
There are three common forms of illness caused by the plague bacteria:
- Bubonic plague is caused when infected fleas bite humans.
- A person can also be infected through a break in the skin.
- This form of plague illness is not contagious.
- Bubonic plague infects the lymphatic system and causes severe swelling.
- The first symptoms appear two to six days after infection and include weakness, high fever, and chills.
- If bubonic plague is not treated, bacteria can spread through the bloodstream, causing septicemic plague or a secondary case of pneumonic plague.
- Later symptoms appear, such as muscular pain, swelling of lymph glands, and seizures.
If untreated, bubonic plague is fatal in more than 50 percent of cases because of progression of the bacteria into the bloodstream.
- This form of the disease infects the lungs.
- It is caused by breathing in aerosolized plague.
- This illness can be transmitted from person to person through respiratory droplets with direct close contact (within 6 feet).
- Symptoms usually surface two to four days (range of one to six days) after exposure.
- Initial symptoms include high fever, cough, and chills, similar to the flu.
- Later symptoms include pneumonia and bloody sputum (coughing up blood).
Without early detection and treatment, the mortality rate from pneumonic plague is nearly 100 percent.
If treated, the mortality rate from pneumonic plague is still 50 percent.
- Septicemic plague may be a secondary illness caused by complications from bubonic or pneumonic plague, or it can occur by itself.
- Plague bacteria enter the bloodstream.
- This form of the disease is not contagious.
- Symptoms appear two to six days after infection.
- Initial symptoms include nausea, vomiting, fever, and chills.
- Later symptoms include low blood pressure, abdominal pain, shock, and, finally, internal bleeding.
Death occurs rapidly if this form of plague is untreated.
Even with treatment, the recovery rate is only 50 percent.
Plague can be difficult to diagnose because its initial symptoms are flulike and the disease progresses so rapidly. Because plague is contagious in the inhaled form, a bioterrorism attack involving plague could go undetected until large groups of people begin exhibiting symptoms.
- If bubonic plague is suspected, physicians check for the presence of a painful, swollen lymph node called a bubo, which occurs no more than 24 hours after initial symptoms.
- Blood cultures, a sputum sample, or examination of a lymph node sample can confirm plague.
- Physicians will ask for a travel history from the patientif he or she has traveled to a known outbreak area.
Treatment of plague with antibiotics must begin immediately to be effective. Containing a plague outbreak involves isolation and other precautions so that plague does not quickly spread in communities and overwhelm the healthcare systems.
- Antibiotics, such as streptomycin, gentamicin, the tetracyclines, and chloramphenicol, are all effective against plague.
- Determining which antibiotic to prescribe depends on patient age and health and on availability of the drug, in addition to the number of cases in an area.
- Antibiotic treatment for pneumonic plague must begin within 24 hours after the first symptoms to be successful.
- Patients with pneumonic plague should be isolated.
- Antibiotics are recommended for people exposed to someone who has pneumonic plague.
- As a precaution, antibiotics may be administered to a person before plague is diagnosed.
There is currently no licensed plague vaccine available in the United States.
Clinical trials on a vaccine for pneumonic plague are underway. For more information, see NIAID's website.
Preventing plague starts with controlling flea and rat populations, the two known carriers of plague.
Insect repellents should be used to prevent flea bites.
People traveling to an outbreak area may be given a three-week course of preventive antibiotics.
Assessing the Risk
Although plague bacteria are under study in many countries, safeguards in these labs would make a potent strain minimally available to terrorists.
Plague is moderately stable in the environment. It can remain infectious for up to an hour after being released into the air, but the organism will break down more quickly if exposed to sunlight or heat.
Terrorists would have to be highly skilled to refine plague into an aerosol attack.
Plague is highly lethal even with treatment.
More information on disasters and emergencies is available at the U.S. Department of Health and Human Service's website: http://www.hhs.gov/emergency