Also called: Bubonic Plague, Septicemic Plague, Black Plague, Yersinia Pestis, Pneumonic Plague
Vikram Tarugu, M.D., AGA, ACG
Plague is an illness resulting from infection with the bacterium Yersinia pestis. Left untreated, it is potentially life-threatening. Plague cases occur only rarely in the United States and are most likely in northern New Mexico, northern Arizona, southern Colorado, southern Oregon, western Nevada and California.
There are three major types of plague:
- Bubonic plague. Historically the most common type of plague to affect humans, it is usually caused by a bite from an infected flea.
- Septicemic plague. Results from plague bacteria that multiply in the bloodstream. This may occur directly from a flea bite or may result as a complication of bubonic or pneumonic plague.
- Pneumonic plague. The least common form of plague, it is nonetheless the most fatal. People typically get pneumonic plague from inhaling infectious droplets coughed into the air by infected people or animals.
Plague cases are most likely to occur in rural areas and urban areas with poor sanitation, large rat populations and overcrowding. Incidences may occur at any time of the year, but are most likely between April and November in the United States.
Symptoms of plague may vary somewhat depending on the nature of the infection. For example, patients with bubonic plague may experience painful, swollen lymph nodes known as buboes. Patients with septicemic plague may experience bleeding from the mouth, nose, rectum or under the skin. Meanwhile, patients with pneumonic plague may have symptoms that resemble those of pneumonia, including bloody sputum, breathing difficulties and chest pain.
Because symptoms of plague can mimic those of other illnesses, various tests may be performed to confirm a plague diagnosis. Once a plague diagnosis has been made, the patient is usually isolated and local and state health departments are notified of the potential health threat to the community. Early treatment is crucial to survive any form of plague. This typically involves intravenous antibiotics.
Controlling rat populations is the best method of preventing plague, because rats and other rodents act as hosts for the bacteria. Antibiotics can be taken as a preventive measure by people bitten by fleas or exposed to the tissues or fluids of animals infected with plague. In recent years, terrorism experts have raised fears that plague bacteria could be turned into an aerosol and sprayed into the air as part of a bioterrorism attack. Officials continue to study the potential for such an attack, ways to prevent it and how to effectively treat those affected by such acts.
Infection with the bacterium Yersinia pestis causes plague. It usually results from being bitten by a flea carrying this bacterium. Left untreated, plague is potentially life-threatening. Although the threat of plague is minimal in the United States, experts have expressed concerns that terrorists may use an aerosol form of the plague as a means of bioterrorism.
Infected fleas are the disease vectors. They transmit plague from one rodent host to another through bites. Humans and other animals that live among rodents also are at risk for being bitten and infected by these fleas. Humans are considered to be accidental hosts for plague bacteria, because rodents are its definitive hosts.
The digestive system of a flea may become blocked with a mass of the Y. pestis bacteria. When a flea with a blocked mass continues to feed, the ingested blood on which it is feeding becomes infected with the bacteria. This infected mixture is then regurgitated by the flea back into the blood source, causing infection.
Less often, plague may enter a person’s body through a break in the skin after the person has had physical contact with an infected animal or its feces. People also can contract plague from eating the meat of infected animals. A form of the illness known as pneumonic plague also can be transmitted through inhalation of infected droplets. Person-to-person transmission of plague is rare and has not been documented in the United States since 1924.
Plague epidemics occur only sporadically in the United States. House rats are the rodents most likely to pose a threat to humans, although the last epidemic in the United States involving house rats occurred in 1924 and 1925 in Los Angeles. Rarely, cases of plague still occur in the United States, but they are usually acquired from fleas found on wild rodents or from physical contact with animals infected with plague.
Throughout the 1980s, there was an annual average of 18 plague cases in the United States, according to the U.S. Centers for Disease Control and Prevention (CDC). Most cases occurred in people under age 20, and about one in seven people with plague died.
In the United States, fleas associated with rock squirrels most often cause infections in the Southwest. Meanwhile, fleas infecting the California ground squirrel are the most likely culprits in the Pacific states. Other animals associated with plague cases in the United States include:
- Cats and dogs
- Deer mice
- Other ground squirrels
- Prairie dogs
- Wild rabbits
- Wood rats
Worldwide, between 1,000 and 2,000 cases of plague occur each year, according to the CDC. Throughout the 1980s, plague outbreaks occurred every year in Africa, Asia and South America. These cases were generally associated with domestic rats and almost always occurred in rural villages.
In recent years, national security experts have raised fears that plague bacteria could be turned into an aerosol and sprayed into the air as an act of bioterrorism. People who inhaled the air would become infected with pneumonic plague. Experts believe that the incubation period would last from one to six days and, because of the delay between the release of the bacteria and the development of symptoms, the disease could quickly become widespread.
In this scenario, large numbers of people would die unless they were promptly treated with antibiotics. Officials continue to study the potential for such an attack and ways to prevent and effectively treat those affected. New early diagnostic methods are under investigation. Public health offices throughout the country have begun stocking large supplies of the medications needed to treat a mass outbreak of plague in the event of such an attack.
Types and differences of plague
There are three major types of plague:
- Bubonic plague. The most common type of plague to affect humans, it is usually caused by a bite from an infected flea. As bacteria travels through the lymphatic system, the bacteria infect the first lymph node they encounter. This typically occurs in the groin, but can also appear in the armpit or neck, depending on the site of the flea bite. The bacteria cause the lymph node to become enlarged and infected. This is called a bubo, and it may swell to between 0.39 inches and 3.94 inches (1 to 10 centimeters) in diameter. The bubo is usually painful and warm to the touch. The pain may be so great that the patient is unable to move the affected body part.
- Septicemic plague. Results from plague bacteria that multiply in the bloodstream. This may occur directly from a flea bite or may result as a complication of bubonic or pneumonic plague. Buboes may be present when the infection is a complication of bubonic plague.
- Pneumonic plague. The least common form of plague, it is nonetheless the most fatal. People typically get pneumonic plague from inhaling infectious droplets coughed into the air by infected people or animals. This is known as primary pneumonic plague. Pneumonic plague may also develop if bacteria spread into the lungs as a complication of bubonic or septicemic plague. This is known as secondary pneumonic plague. Pneumonic plague progresses rapidly and can cause respiratory failure within two days of infection. Usually, antibiotics must be administered within the first 24 hours after symptoms appear, or death can occur. More than half of patients with pneumonic plague that is not timely treated results in death, according to the U.S. Centers for Disease Control and Prevention.
Risk factors and causes of plague
Plague occurs due to infection with the bacterium Yersinia pestis. This typically occurs when a person is bitten by a flea carrying the bacteria. Fleas may become exposed to the bacteria after biting rats carrying the bacteria. Rats and other rodents act as hosts for the bacteria that cause plague. Thus, people living under unsanitary conditions in areas with large rat populations have an increased risk of infection.
Plague cases are most likely to occur in rural areas and urban areas with poor sanitation, large rat or other rodent (e.g., chipmunk) populations and overcrowding. Cases may occur at any time of the year, but are most likely between April and November in the United States.
North American plague cases occur from the Pacific coast eastward to the western Great Plains, and from the Canadian provinces of British Columbia and Alberta southward to Mexico. Two regions experience most of the plague cases in the United States. The first is northern New Mexico, northern Arizona and southern Colorado. The second is in California, southern Oregon and the westernmost portion of Nevada. All of these regions have large wild rodent populations.
People who work with animals or live in close proximity to certain animals are at higher risk for plague infection. Such groups include campers and hikers, dog or cat owners, hunters and veterinarians.
Signs and symptoms of plague
Symptoms of plague may vary depending on the nature of the infection.
Bubonic plague tends to appear between two and six days after a person is exposed to the bacteria. Patients typically experience painful, swollen lymph nodes known as buboes. Other symptoms may include:
- Muscle aches
If the bacteria associated with bubonic or pneumonic plague spreads to the bloodstream, septicemic plague may develop. Sometimes, this condition also develops on its own without the presence of bubonic plague. Symptoms of this illness include bleeding from the mouth, nose, rectum or under the skin. Other symptoms may include:
- Abdominal pain
- Blackening and death of tissue (gangrene) in the extremities (e.g., fingers, nose, toes)
- Shock (a condition resulting from inadequate blood flow)
Pneumonic plague may develop on its own or as a complication of bubonic or septicemic plague. The incubation period for pneumonic plague is between one and three days. Symptoms resemble those of pneumonia, including bloody sputum, breathing difficulties and chest pain. Other symptoms may include:
- High Fever
- Nausea and vomiting
Diagnosis and treatment of plague
In diagnosing plague, a physician will perform a complete physical examination and compile a thorough medical history. Plague may be suspected if there has been a recent case of the illness in the community. The physician may also ask about recent travel to areas with frequent outbreaks of plague or any recent incidences of exposure to sick animals.
Because symptoms of plague may mimic those of other illnesses, a physician will also likely look for a visible bubo (painful, swollen lymph nodes) that might indicate the presence of bubonic plague. Examination of lymph node specimens (e.g., fluid samples drawn with a needle from a bubo) can help confirm the diagnosis. In diagnosing pneumonic plague, a thin, flexible tube (endoscope) may be inserted through the mouth or nose and down the throat to extract fluid from the airways. Blood tests may be performed to look for the presence of Y. pestis bacteria if septicemic plague is suspected.
Once a plague diagnosis is made, the patient is usually isolated and local and state health departments are notified of the potential health threat to the community. Intravenous antibiotics will be administered, typically over a period of at least 10 days. The antibiotic of choice is steptomycin, but other antibiotics (e.g., chloramphenicol, tetracycline) are also effective against plague. Serious complications may require treatment such as respiratory support, intravenous fluids, steroids and oxygen. Early treatment is crucial to survive any type of plague. For example, patients who have pneumonic plague but do not begin treatment within 24 hours of initial symptoms have a greatly increased risk of death. Researchers are investigating new methods of early detection of plague.
Prevention methods for plague
Controlling rat populations is the best method of preventing plague. This has been partially achieved in some areas of the world, but remains a widespread problem in many developing nations. People who live in areas with substantial rat populations, or large wild rodent populations, are encouraged to ensure that their residence is rodent-proof. Rodents may enter residences through almost any sized hole in the building structure.
Once a case of plague has been diagnosed, local and state health departments will take measures to reduce the spread of the illness. Officials will closely monitor both the local human and rodent populations for signs of plague and may use insecticides to reduce the number of fleas in an area. Patients diagnosed with plague will be isolated to avoid spread of the disease.
In regions such as the American West, plague tends to be more widespread in wild rodents (e.g., chipmunks, prairie dogs). People living in these areas are urged to eliminate potential food and shelter sources for these rodents. This includes removing brush, rock piles, junk and food sources from properties. People are urged not to pick up or touch dead or sick animals, but instead to report them to local health department or law enforcement officials.
Treating pets for fleas on a regular basis also can help reduce the risk of plague among domestic pets. Using certain types of insect repellents when outdoors may help prevent flea bites in humans.
Antibiotics may be taken as a preventive measure by people bitten by fleas or exposed to the tissues or fluids of animals infected with plague. Antibiotic treatment also may be advisable for people who have had close physical contact with an infected person, or who are planning to spend time in an area with recent cases of plague. At one time, a plague vaccine was available in the United States. However, the efficacy of the vaccine was never established, and it is no longer is produced. Potential new vaccines are being studied.
Questions for your doctor regarding plague
Preparing questions in advance can help patients to have more meaningful discussions with their physician regarding their conditions. Patients may wish to ask their doctor the following questions related to plague:
- Do my symptoms indicate plague?
- How will you diagnose plague?
- What type of plague do you suspect?
- How serious is my illness?
- What are my treatment options?
- What are the risks associated with these treatments?
- How long will I have to take antibiotics?
- How will I know if treatment has been effective?
- What tips do you suggest for preventing plague?
- Should I take antibiotics as a preventive measure?