Plague is a life-threatening infection caused by the organism Yersinia pestis. There are three types of plague. Bubonic plague is the most common type in humans. Infected fleas transmit Y. pestis primarily among rodents. When an outbreak kills many rodents, infected fleas can jump to other animals and humans, spreading the infection. Improved living conditions and health services have made human outbreaks uncommon, but occasional plague cases occur. Concern exists about the use of plague as a biological weapon. Plague bacteria could be put into a form that might be sprayed through the air, infecting anyone inhaling it and causing pneumonic plague. This form affects your lungs and can spread from person to person. Fortunately, when given promptly, antibiotics usually effectively treat plague.
Complications of Plague
Complications of plague may include:
With prompt treatment, the overall fatality rate from plague is less than 15 percent. Without treatment, mortality rates can be as high as 60 percent for bubonic plague and 100 percent for pneumonic plague. Death can occur within days after symptoms first appear if treatment doesn't begin promptly.
Causes of Plague
Plague has afflicted humans throughout history. The cause of plague, the Yersinia pestis bacterium, was discovered in 1894 by Alexandre Yersin. Soon after, scientists realized that fleas transmitted the bacteria. Three types of plague exist.
Bubonic plague is the most common type of plague in humans. It's usually caused by a bite from an infected flea. Y. pestis bacteria primarily infect animals such as squirrels, rabbits and prairie dogs. You may become infected by a fleabite if you're in close contact with such animals. The bacteria can also enter through a cut in your skin if you handle these animals. Domestic cats that come into contact with infected animals also may transmit the infection to humans.
Septicemic plague occurs when plague bacteria multiply in your bloodstream. This happens when bacteria transmitted by a fleabite enter directly into your bloodstream, or as a complication of bubonic or pneumonic plague.
Secondary pneumonic plague can develop if you're infected with another type of plague. In this case, the infection spreads to your lungs, causing a virulent pneumonia that can often be fatal. Primary pneumonic plague can occur when you inhale droplets coughed into the air by a person or animal with pneumonic plague.
Plague as a bioterrorism agent
Plague is also one of a number of potential agents of bioterrorism, along with anthrax, smallpox, botulism, tularemia and nerve gases. It's possible that plague bacteria could be turned into an aerosol and then be spread over large populations.
Signs & Symptoms of Plague
There are three types of plague: bubonic, septicemic and pneumonic. Signs and symptoms vary depending on the type of plague. It's possible to develop more than one type.
Signs and symptoms of bubonic plague generally appear within two to eight days of a plague-infected fleabite. After you're bitten, the bacteria travel through your lymphatic system, infecting the first lymph node they reach. The resulting enlarged lymph node (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.
Signs and symptoms of bubonic plague include:
Septicemic plague occurs when plague bacteria multiply in your bloodstream. If septicemic plague occurs as a complication of bubonic plague, buboes may be present.
Signs and symptoms include:
Pneumonic plague — which can occur as a complication of another type of plague or by inhaling infectious droplets coughed into the air by a person or animal — is the least common form of plague. But it's also the most rapidly fatal. Early signs and symptoms, which generally occur within a few hours to a few days after inhaling contaminated droplets, include:
Pneumonic plague progresses rapidly and may cause respiratory failure and shock within two days of infection. If antibiotic treatment isn't initiated within a day after signs and symptoms first appear, the infection is likely to be fatal.
Diagnosis of Plague
Your doctor may suspect plague if you live in a high-risk region or report a suspicious exposure. With the exception of a visible bubo, signs and symptoms often mimic other, much more common infectious diseases.
You'll likely be asked to describe the type and severity of your symptoms and tell your doctor about your recent history, including whether you've been exposed to sick animals or traveled to areas with plague.
Bubo and respiratory fluid examination
If plague is suspected, your doctor may confirm the diagnosis through microscopic examination of fluid extracted from your bubo, bronchi or trachea. Needle aspiration is used to obtain fluid from your bubo. Fluid is extracted from your airways using endoscopy. In this procedure, a thin, flexible tube is inserted through your nose or mouth and down your throat. A suction device is sent down the tube to extract a fluid sample from your airways.
Your doctor may also test blood drawn from your veins to diagnose plague. Y. pestis bacteria generally are present in your bloodstream only if you have septicemic plague.
Treatments of Plague
Treatment for plague includes antibiotics and supportive therapy. Your doctor is required by law to report documented plague infections to local health officials.
As soon as your doctor suspects that you have plague, you'll need to be admitted to an isolation room in a hospital. There, you'll receive powerful antibiotics directly into your veins (intravenously) or your muscles (intramuscularly) for seven to 10 days. Streptomycin and gentamicin are the most effective drugs against plague. Other alternatives include intravenous doxycycline (Vibramycin) and chloramphenicol (Chloromycetin).
Even if you don't have signs or symptoms, you'll need treatment with preventive, oral antibiotics for seven days after direct exposure to a person with pneumonic plague.
If you have serious complications, such as bleeding, organ failure and respiratory distress, then respiratory support, intravenous fluids and oxygen may be necessary.
Prevention of Plague
Although no effective vaccine is available, antibiotics offer effective preventive therapy if you're at risk of or have been exposed to plague. Ask your doctor immediately about preventive antibiotics if you:
Take the following precautions if you live or spend time in regions where plague outbreaks occur:
Know the risk factors and the symptoms of plague so that you can identify it early and contact your doctor immediately. If you know of recent plague cases in your area, report sick or dead animals to your local health department or to police.
When to seek Medical Advice
Call your doctor if you or someone close to you develops signs or symptoms of plague within a week of any of the following: