What is the plague, what are its causes and symptoms?

Plague is a deadly bacterial infection that has swept the world in several pandemics, especially in past centuries, causing the extinction of about a third of humanity at the time.

The paradox of this disease is that the stronger the killer, the smaller the carrier. In fact, plague is transmitted from animal to human and from human to human by the mere bite of a small flea.

In the Middle Ages, the plague was known as the Black Death. According to ancient sources, it originated in Central Asia or India. These countries were the home of the famous Silk Road trade route and many military routes to Europe.

Through traders and soldiers, the plague spread mainly to the port cities of Europe and from there to the rest of the world.

The high death rate from the plague was also caused by cruel wars, harsh "ice" weather, famine. Other pandemics that occurred at the same time as anthrax or other mostly viral diseases also contributed.

The last major plague pandemic occurred in London, ending in 1666 after the Great Fire of London, which killed off most of the black rats that were the reservoir of the plague carrier, the flea. Worldwide, the plague claimed an estimated 200 million victims.

However, the disease has never been completely eradicated from the world, which is why you can still encounter the plague today. Approximately 5,000 people contract the plague each year.

If the infection is not diagnosed early and treatment with antibiotics is not started, the disease can still cause death quite quickly today.

Plague is a bacterial infection transmitted by the bacterium Yersinia pestis. It is a rod-shaped, elongated bacterium of the Enterobacteriaceae family without flagella.

This micro-agent of the deadly disease was discovered in 1894. Two scientists, Alexander Yersin and Shibasaburo Kitasato, were responsible for this important discovery. The bacterium was named after the former.

Yersinia pestis is transmitted by the bite of a flea that has previously bitten and sucked the blood of an infected animal or human.

The most commonly infected animals include:

• Rats
• Mice
• Squirrels
• Rabbits
• Prairie dogs
• Squirrels
• Voles

The bacteria survives and multiplies in the flea's digestive tract. After a period of time, the flea's digestive tube becomes clogged with large amounts of bacteria and the flea begins to starve.

The starved flea becomes more aggressive. It also bites animals that are not normally part of its "diet", such as humans. After the bite, the bacteria enter the human bloodstream and the flea starves to death.

In addition to transmission by flea, humans can also become infected through direct contact with infected animal blood, for example through tiny tears in the skin. Pets, especially cats and dogs, can become infected with Yersinia by hunting and eating infected rodents.

The pneumonic form of plague is spread by droplet infection. It mainly affects the lower respiratory tract and is one of the most deadly forms of plague. Tiny droplets containing the bacteria are released into the air when an infected individual coughs and sneezes.

Nowadays, the risk of contracting the plague is very low, yet several thousand people are infected each year.

Risk factors for contracting the disease include:

• Residence in countries with an increased incidence of plague, such as overcrowded rural and semi-rural areas with poor hygiene habits and a high proportion of rodents, especially black rats and rats. The most risky areas for plague are African countries, especially the island of Madagascar, parts of Asia and America, especially New Mexico, Arizona, California and Colorado.
• Occupations that involve contact with animals are also at risk, especially veterinarians and their assistants. The most risky occupations are the treatment of pets, cats and dogs in areas at risk.
• Frequent movement and outdoor activities such as camping, hunting or hiking in areas where animals infected with plague are found.

Plague has three main forms in which it can manifest itself in humans: bubonic, septic and pneumonic plague.

Bubonic plague, bubonic plague, black plague

Bubonic plague is the most common form of the disease. Its name is derived from its most striking symptom, namely swollen and swollen lymph nodes (buboes). Swollen lymph nodes appear about a week after infection with the plague.

Infected lymph nodes are:

• most commonly in the groin, armpit or neck
• are the size of a chicken egg
• the skin over them is sensitive but firm to the touch

Other symptoms of bubonic plague include:

• sudden onset of fever and chills
• headache
• fatigue or malaise
• muscle pain

Septicemic plague

Septicemic plague is a form of the disease in which Yersinia pestis bacteria are released into the bloodstream.

They continue to multiply in the bloodstream and clog small blood vessels, especially in the extremities of the body such as fingers and toes, tip of the nose, earlobes, etc. The unblooded tissue dies, causing gangrene and blood poisoning.

Symptoms of septicemic plague include:

• Fever and chills
• General weakness
• Abdominal pain, diarrhea and vomiting.
• Bleeding from body orifices, mouth, nose, rectum or under the skin
• Shock
• Blackening and death of tissue (gangrene) on the extremities, most commonly the hands, feet and nose

Lung plague

Pneumonic plague is the most serious form of plague. Fortunately, it is the least common. Pneumonic plague is spread from person to person by droplets that an infected individual coughs or sneezes.

Symptoms appear relatively quickly after infection and progress within a few hours. Without prompt therapeutic intervention, the person dies quickly.

The symptoms of pneumonic plague are:

• Coughing with bloody mucus (sputum)
• Difficulty breathing
• Nausea and vomiting
• High fever
• Headache
• Weakness
• Chest pain

When plague is suspected, the basic diagnostic test is the identification of the causative organism, i.e. Yersinia pestis.

The bacterium is detected in samples taken from the affected tissue:

• In bubonic plague, the tissue of the nodule is taken by biopsy or aspiration from the nodule.
• In septicemic plague, the bacterium is found in the bloodstream and in blood taken by venipuncture.
• The pulmonary form of plague is confirmed by collecting and examining sputum, or coughed-up mucus. If sputum cannot be coughed up, the fluid used to lavage the airways during bronchoalveolar lavage may also be examined.

The course of infection depends on which form a person develops. Pneumonic plague is the most rapidly progressive and deadliest. Within hours of the first symptoms, sudden respiratory failure and shock occur, ending in death within about two days of infection.

Most patients affected by the bubonic form of plague survive after rapid antibiotic treatment.

Septic plague has a dramatic course. Within days of infection, numerous gangrenous lesions begin to form on the body.

Blood clots and bacteria in the small blood vessels of the arms and legs clog them and prevent blood flow. This causes the tissue to die.

The rapid therapeutic intervention is amputation, the removal of dead body parts. If amputation is not proceeded with, blood poisoning quickly occurs, which is the cause of death.