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The Plague, sometimes called Black Death, was the most devastating disease in the history of humankind. Between 75 million and 200 million people died because of it.
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What Is The Plague?
The plague is an infectious disease caused by a bacterium named Yersinia pestis, a pathogen which invades the cells of the human body or other mammals, like rats. Its power lies in the fact that it is very infectious and it is able to avoid the immune system of its host.
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Yersinia pestis
A bacterium is a simple 1 cell microorganism, shaped like a rod. It only needs food supply and a host (if it is a pathogen) to survive and to reproduce.
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Multiplication
Bacteria reproduce by binary fission, a process in which one microorganism duplicates its DNA and then splits into 2 microorganisms. If the host is suitable, many binary fissions occur, resulting in thousands of new microorganisms.
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Host
Inside humans, Yersinia pestis lives in the blood and lymphoid tissues, where it is able to avoid the attack of the immune system. It is also found in the reticuloendothelial system, which are immune response-related cells and tissues located throughout the body.
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Power
The success of Yersinia pestis as a pathogen relies on its ability to suppress and to avoid immune system response like antibody production. By injecting proteins into macrophages (cells that engulf), Yersinia pestis resists being eaten.
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Discovery
French/Swiss bacteriologist Alexandre Yersin discovered the pathogen in 1894, at the time of an outbreak in Hong Kong. Over a century later, in 2010, researchers confirmed that Yersinia pestis had been responsible for the plague.
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How Is a Person Infected by The Plague?
The bacteria that cause the plague circulate among rodents such as mice and squirrels, and particularly black rats. They can be transmitted to humans in at least 3 different ways: rat flea bites, contact with contaminated tissue, or infectious droplets.
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Black Rats
Yersinia pestis lives in rodents including black rats. The rats can be found living in the wild in rural areas, as well as in urban regions, where they live close to humans.
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Rat Fleas
Parasites that live on and around black rats, rat fleas feed on the blood of rodents. When infected with bacteria, they work as a vector for the plague, as well as for other deadly diseases.
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Rat Fleas on Humans
If a rat flea bites a rat that is infected with Yersinia pestis, the rat flea transports the bacteria to the human body when it bites the human. Rat fleas also spread the bacteria among rats and other rodents.
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Infectious Droplets
An infected person can transmit the plague by coughing. When they cough, droplets containing the plague bacteria are dispersed into the air, and can be breathed in by another person.
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Symptoms and Treatment
The plague can take different clinical forms, with bubonic plague, pneumonic plague, and septicemic plague being the most frequent.
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Some symptoms are quite easy to see and diagnose due to their unique appearance, while other signs of the infection have much in common with other diseases.
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Buboes
Through the bite of an infected flea, the bacteria infect the lymph node system. Painful inflammation and swelling often appears in the armpit and groin and can limit movement in those parts of the body.
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Common Symptoms
Pneumonic plague patients may experience high fever, chills, cough, and breathing difficulty. They may even cough up blood. Signs of septicemic plague include nausea, vomiting, diarrhea, and abdominal pain.
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Black Skin
Skin and other tissues affected by the bacteria may die and then turn black. Buboes can remain on the body for up to a week, and may even burst by themselves.
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Pneumonic Plague
When the infection reaches the lung, this is the most serious form of the disease. In this phase, the plague can be transmitted between humans by coughing.
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Antibiotics
The most efficient treatment for the plague in any of its forms consists of early administration of antibiotics. If a patient receives no medication, the possibility of death is very high, almost certain.
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Origins of The Plague
The Black Death, also known as the Great Plague, began in China in 1334. It traveled all over Asia, most likely with the Mongol army. It also spread by the way of the Constantinople trade routes before it arrived in Europe 13 years later.
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Origin
By unknown circumstances, Yersinia pestis woke up from its slumber in Asia. It easily passed into the bloodstreams of black rats that lived very near to humans in the 14th century.
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Medieval Conditions
At that time, poor hygienic conditions favored the spread of the plague. Bacterium moved along trade routes in the blood of rats and in rat fleas. Rapidly, the plague spread all over Asia and it reached Crimea, near Europe.
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Port City of Kaffa
The plague was introduced to Europe at the trading city of Kaffa. Genoese merchants escaped desperately and they unknowingly took the infection to Venice. From Italy, the plague spread rapidly to the entire continent. In 7 years, 60% of the European population passed away.
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The Plague Today
Many outbreaks of the plague have occurred over time. After the appearance of antibiotics, it is a deadly but controlled disease. The key is early diagnosis and treatment. The earlier a patient seeks medical attention, the better the chances of recovery.
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Diagnosis is made by analyzing samples of the patient, taken from blood and lymph glands.
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Africa
Many outbreaks occurred in Europe and Asia, like the third pandemic in China in 1860. During this epidemic, scientists identified the causative agent and disease control started to improve.
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Today, the plague exists mostly in some African countries, where 95% of the world’s cases take place.
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Last Reported Outbreak
Between 2000 and 2009, a little more than 20,000 people became infected. One of the more recent reported outbreaks took place in Madagascar, resulting in 119 cases and 40 deaths.
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Diagnosis
Diagnosis consists of analyzing blood and lymph gland samples from patients. But first of all, people must know the symptoms and pay attention if they appear. If diagnosis is positive, treatment must start as soon as possible.
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Treatment
According to the World Health Organization (WHO): “When rapidly diagnosed and promptly treated, plague may be successfully managed with antibiotics reducing mortality from 60% to less than 15%.”
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Prevention
There are many different things that humans can do to keep from catching the plague and also to prevent the spread of the illness, as well as outbreaks. Prevention is actually the most effective way to control this often deadly disease.
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Avoid Contact with Rats
Not only avoid direct contact, but also eliminate everything that may attract rats. Remove rock piles and junk that could be used for rat nests along with possible food supplies, such as pet food.
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Gloves
Wear gloves if handling any sick or dead animals, tissues, or droppings that may potentially be infected. It’s also good to use face and eye protection in these cases.
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No Fleas
Use repellents that contain DEET to avoid contact with fleas, especially during outdoor activities like camping and hiking. Eliminate these parasites from the home to reduce the risk of bites.
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Pets
Beware of stray dogs and cats, as they are often infested with fleas. Also use flea-control products on any pets that normally roam freely in more rural areas.
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Plague Vaccine
Used to immunize people in animal plague areas, plague vaccine is not available in all countries. As it is not very effective against pneumonic plague, the World Health Organization (WHO) doesn’t recommend it for high-risk groups.