Topic Resources
Plague is a severe infection caused by the gram-negative bacteriaYersinia pestis and often involving the lymph nodes and/or lungs.
-
The bacteria are spread mainly by the rat flea.
-
Depending on the form, plague can cause fever, chills, swollen lymph nodes, headache, a rapid heartbeat, cough, difficulty breathing, vomiting, and diarrhea.
-
Identifying the bacteria in samples of blood, sputum, or pus from lymph nodes confirms the diagnosis.
-
Antibiotics can reduce the risk of death, and isolating infected people helps prevent spread of plague.
In the past, massive plague epidemics, such as the black death of
the Middle Ages, killed many people. The main contributing factors were
large numbers of rodents, urban crowding, and poor sanitation.
Plague now occurs mostly in rural areas.
In the United States, more than 90% of infections occur in
southwestern states such as Arizona, California, Colorado, and New
Mexico, particularly among campers. In recent decades, plague affects an
average of about 7 people a year (ranging from 1 to 17 people) in the
United States.
Worldwide, 3,248 cases were reported from 2010 to 2015, including
584 deaths. Since the 1990s, most cases have occurred in Africa, with
recent outbreaks in Madagascar.
Transmission
The bacteria that cause plague usually infect wild rodents, such
as rats and prairie dogs. The bacteria are spread by the rat flea. When
wild rats die, the fleas may move to rats that live close to people,
then to household pets, especially cats. The rat fleas may then bite
people and transmit infection. People may also become infected through a
break in their skin if they have direct contact with an infected
animal.
Rarely, the infection is spread from person to person by inhaling
droplets dispersed by coughing or sneezing. The bacteria lodge in the
lungs and cause a type of pneumonia
(pneumonic plague). Spread between people usually happens only when
people live with or care for a person with pneumonic plague.
Plague bacteria are a potential biological weapon.
The bacteria can be spread through the air and inhaled. The size of the
airborne particle determines where the bacteria lodge in the
respiratory tract. Small particles lodge in the lungs, causing pneumonic
plague. Larger particles lodge in the throat (pharynx) and cause plague
of the throat (pharyngeal plague).
Symptoms
Plague has several forms:
-
Bubonic
-
Pestis minor
-
Pneumonic
-
Septicemic
Symptoms vary depending on the form of plague.
Bubonic plague
Bubonic plague is the most common form.
Bubonic plague symptoms may appear a few hours to 12 days after
exposure (typically, after 2 to 5 days). Chills and fever of up to 106° F (41° C) occur suddenly. The heartbeat becomes rapid and weak, and blood pressure may drop. Many people become delirious.
Shortly before the fever or at the same time, lymph nodes near
the flea bite or scratch, usually in the groin or armpit, become swollen
and painful. These swollen lymph nodes are called buboes. They are
firm, red, warm, and very tender. During the second week, pus may drain
from the lymph nodes. The liver and spleen may enlarge.
A bump, sore, or a black scab may form at the site of the flea bite.
People with bubonic plague may become restless, delirious, confused, and uncoordinated.
Because the bacteria can spread through the bloodstream, the lungs may be affected, causing pneumonic plague.
A Plague Bubo
Image courtesy of
Drs. Margaret Parsons and Karl F. Meyer via the Public Health Image
Library of the Centers for Disease Control and Prevention.
More than 60% of untreated people die, usually between the third and fifth day.
Pestis minor
Pestis minor is a mild form of bubonic plague. Its
symptoms—swollen lymph nodes, fever, headache, and exhaustion—disappear
within a week.
Pneumonic plague
Pneumonic plague is infection of the lungs.
Pneumonic plague symptoms begin abruptly 2 or 3 days after
exposure to the bacteria. People have a high fever, chills, a rapid
heartbeat, and often a severe headache. Within 24 hours, they develop a
cough that brings up clear sputum, which soon becomes flecked with
blood. Then the sputum becomes pink or bright red (resembling raspberry
syrup) and foamy. Breathing is rapid and labored.
Most untreated people die within 48 hours after symptoms start.
Septicemic plague
Septicemic plague is infection that spreads into the blood. About
40% of people have nausea, vomiting, diarrhea, and abdominal pain.
Eventually, blood clots too much, blocking blood vessels and
eventually causing bleeding because clotting factors are used up. This
disorder is called disseminated intravascular coagulation. Because blood flow is blocked, gangrene develops in the limbs, which may turn black (hence, the name Black Death).
Without treatment, many organs malfunction, often causing death.
Diagnosis
-
Examination and culture of samples of blood, sputum, or pus
-
Sometimes other blood tests
Rapid diagnosis of plague is important because the longer treatment is delayed, the higher the risk of dying.
To diagnose plague, doctors take samples of blood, sputum, or pus
from lymph nodes. Samples are examined under a microscope and sent to a
laboratory to grow (culture) bacteria. The blood sample is also tested
for antibodies to the bacteria. Tests that rapidly detect the bacteria
or its genetic material (DNA), such as polymerase chain reaction (PCR),
may be done.
If doctors suspect pneumonic plague, a chest x-ray is taken.
Prevention
The following measures can help control rodents and prevent flea bites:
-
Removing anything that might attract rodents (such as brush, rock piles, junk, cluttered firewood, and food) from around homes
-
Wearing gloves when handling animals that may be infected (for example, when skinning an animal)
-
Using repellents, such as DEET (diethyltoluamide) when exposure to rodent fleas is possible (for example, while camping, hiking, or working outdoors)
-
Applying products that control fleas to pets
-
If pets roam outside in areas where plague is present, not letting them sleep in a person's bed
The vaccine against plague is no longer available in the United States.
People who are traveling to locations with a plague outbreak may take an antibiotic such as doxycycline.
After exposure to plague
Doctors monitor people who have had contact with a person who has
pneumonic plague. Their temperature is taken every 4 hours for 6 days.
Also, antibiotics are given to prevent the infection from developing. Adults are given doxycycline or ciprofloxacin, and children are given trimethoprim/sulfamethoxazole.
Treatment
-
Streptomycin or another antibiotic
Treatment of plague begins immediately and reduces the risk of
death to less than 5%. For pneumonic or septicemic (bloodstream) plague,
antibiotics must be started within 24 hours after symptoms appear.
Streptomycin is given
by injection into a muscle for 10 days or until 3 days after temperature
has returned to normal. Other antibiotics such as gentamicin, doxycycline, and ciprofloxacin are also effective.
People with pneumonic plague must be isolated so that they do not
spread the bacteria through the air—called respiratory isolation.
Respiratory isolation includes the following:
-
Limiting access to the room
-
Requiring people who work near an infected person to wear a mask, eye protection, a gown, and gloves
More Information
Other Yersinia infections
Other Yersinia species, such as Yersinia enterocolitica and Yersinia pseudotuberculosis, infect animals worldwide. These bacteria can be transmitted to people but cause a less severe illness than plague.
Infections caused by other Yersinia bacteria can also be
acquired by handling infected animals (for example, by hunters), by
eating undercooked meat from infected animals, or by drinking
contaminated water.
These infections commonly cause diarrhea, which usually resolves
on its own, and sore throat. Lymph nodes in the abdomen become inflamed,
causing pain in the lower right part of the abdomen. The pain resembles
the pain of appendicitis.
The bacteria may infect the bloodstream, but they rarely spread to parts of the body outside the intestinal tract.
Prevention of other Yersinia infections involves the following:
-
Washing hands with soap and water before eating and preparing food, after contact with animals (especially their feces), and after handling raw meat
-
Cooking meat to recommended temperatures
-
Consuming only pasteurized milk and dairy products
-
Disposing of feces of pets in a sanitary way
Treatment of other Yersinia infections focuses on relieving the diarrhea. These infections usually resolve on their own. However, antibiotics are needed if the infection has spread to the bloodstream or other organs.
Posts
0 Comments