Bubonic Plague

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Bubonic plague

Bubonic plague is a contagious, deadly disease caused by the bacterium Yersinia pestis. Sometimes referred to simply as "the plague," this disease has played a major role in world history. Because plague is highly contagious, it is easily transmitted from one person to another. Worldwide epidemics of the disease (called pandemics) have decimated populations since a.d. 542, when the first evidence of plague was recorded. Plague is rarely seen in the United States today, but is still epidemic in Southeast Asia .

Transmission of bubonic plague bacteria

Yersinia pestis is an intracellular parasite. In contrast to other kinds of bacteria , it enters cells. The bacterium that causes tuberculosis is also an intracellular parasite, as is the bacterium that causes chlamydia, a sexually transmitted disease.

Humans are not the "first choice" of host for Yersinia pestis. The Yersinia pestis bacterium infects the bloodstream of rats and other wild rodents such as squirrels and prairie dogs. Humans become infected only through the bite of a flea that has ingested blood from an infected rodent. Another route of transmission is through person-to-person contact. If a person's lungs are infected with the bacteria, the disease can be transmitted easily to another person through a cough or a sneeze. This form of transmission is extremely quick: cases have been recorded of persons dying from the disease within 24 hours of exposure to an infected person.

Symptoms of bubonic plague

In humans, plague can take two forms. One form, called the bubonic form, usually results from a flea bite and is characterized by a sore called a bubo. The bubo is actually the infected lymph node that drains the area through which the bacteria was introduced by the infected flea. The lymph node enlarges and turns black. Other symptoms of this form of plague include fever and congestion of the blood vessels of the eye . As the disease progresses, the bacteria spread to other parts of the body, resulting in septicemia, or widespread infection . The fatality rate of the bubonic plague is 15%.

In another form of plague, called the pneumonic form, the bacteria infect the lungs. This form of plague can follow the bubonic form, as the bacteria spreads to the lungs. Or, a person may simply contract the pneumonic form only, and show no evidence of a bubo. The pneumonic form is highly contagious and especially virulent: the average length of time from the first appearance to symptoms to death is less than two days.

For both types of plague, antibiotics can cure the disease. A vaccine is also available to protect those who are at risk of contracting plague. People who work with Yersinia pestis in laboratories and in environments where wild rodents are infected with the bacteria usually are vaccinated against plague. United States soldiers who fought in the Vietnam war in the 1960s and 1970s were vaccinated against plague. However, the vaccine only protects against the bubonic form, not the pneumonic form. People who are exposed to the pneumonic disease should take antibiotics as a precautionary measure.

Plague pandemics

Plague has played a major role in world history. Some evidence exists that a plague pandemic took place about 2,000 years ago, but the first recorded pandemic of plague occurred in a.d. 542 in Egypt and Ethiopia. This pandemic killed 100 million people.

The next great plague pandemic occurred in the fourteenth century in Europe , Central Asia, the North East, India, and China. In this pandemic, trading ships from China carried infected rats to Europe. About 25 million people in Europe alone died from plague; some experts estimate that this number constitutes a third of the European population. Because so many people died, the plague had a major impact on the economy and political structure of Europe. The scarcity of workers led to a scarcity of food; workers, previously given little compensation for their labors, began to demand higher wages. Some historians feel that the unrest of workers and the middle class in Europe that culminated in the beheading of King Charles I in England in the seventeenth century and the beheading of Louis XVI in France in the eighteenth century had its roots in the economic aftermath of the fourteenth plague pandemic.

The third plague pandemic began in Burma in 1894; from there, the plague spread to China and through Hong Kong to North America . One hundred million people in India died from plague over a period of 20 years. During this pandemic, the United States saw its first case of plague in 1900 in San Francisco. In 1907, 167 cases of plague in San Francisco were recorded. As a result of the pandemic, rats and other wild rodents in the areas around San Francisco became reservoirs of Yersinia pestis. Today, isolated cases of plague are still found in Kansas, Oklahoma, and Texas. The majority of cases worldwide (90%) occur in Southeast Asia: Burma, South Vietnam, Nepal, and Indonesia. Brazil also has a high number of plague cases. A recent outbreak in Surat, India, in 1994, killed 56 people and caused widespread panic.

Prevention

Plague pandemics can be prevented by the disinfection of ships, aircraft , and persons who are known to have the plague. The classic route of transmission that leads to pandemics is the transportation of infected rodents aboard transcontinental vehicles. Since many countries have instituted rigorous disinfection practices for ships and planes, plague cases have dropped dramatically.

If a person is diagnosed with plague, most countries, including the United States, require that the governmental health agency be notified. The person is usually kept under strict quarantine until the disease is brought under control with antibiotics.

Another way to prevent plague is to control rodent and flea populations in cities. Fleas are easier to control than rodents, since most homes can be easily decontaminated. Many cities, especially in the United States, have instituted rodent-control programs aimed at decreasing the numbers of rodents that roam the streets. Since rodents also carry rabies and other deadly diseases, controlling their numbers makes sense for a variety of reasons.