What bacteria causes the plague?

Plague is a serious disease caused by a specific bacterium known as Yersinia pestis [1]. This bacterium can infect small mammals, especially rodents, as well as humans. Plague is one of the diseases that historically led to widespread pandemics, such as the one that killed millions of people in Europe during the Middle Ages [3]. Although it is rare today, it still exists in some regions around the world and can be treated effectively with antibiotics if detected early [1].

How is the plague bacterium transmitted?

The Yersinia pestis bacterium is transmitted to humans in several ways, most notably through the bites of infected fleas that carry the bacterium from infected rodents [1]. Pets, such as dogs and cats, can carry infected fleas into homes, increasing the risk of infection transmission [1]. People can also become infected through direct contact with an infected animal, such as touching body fluids or tissues, as happens with hunters who skin infected animals [1]. In rare cases, pneumonic plague—a form of the disease—can spread through the inhalation of respiratory droplets from an infected human or animal [1].

Types of plague and their symptoms

There are three main types of plague, which differ in the areas they affect and their symptoms:

• Bubonic Plague: This is the most common form and affects the lymph nodes. Symptoms appear suddenly 2 to 8 days after exposure and include fever, chills, headache, and muscle aches, as well as painful, swollen lymph nodes known as "buboes," which often appear in the groin, armpit, or neck areas [1].
• Septicemic Plague: This occurs when bacteria multiply in the bloodstream. It can result from a flea bite or handling an infected animal, or it may develop from untreated bubonic plague. It can lead to death even before severe symptoms appear. Its symptoms include abdominal pain, bleeding, diarrhea, fever, nausea, vomiting, extreme weakness, shock, and tissue death (skin turning black) on the fingers, toes, and nose [1].
• Pneumonic Plague: This is the most dangerous form of plague and affects the lungs. It can spread between humans through the inhalation of respiratory droplets from an infected person or animal [1]. Symptoms appear suddenly 1 to 3 days after exposure and include severe cough, difficulty breathing, chest pain, weakness, fever, chills, headache, frothy bloody sputum, respiratory failure, and shock [1].

Diagnosis and treatment

Plague is diagnosed through a physical examination and review of symptoms, as well as laboratory tests such as blood cultures, culture of fluid taken from swollen lymph nodes, or sputum cultures [1]. Immediate treatment with antibiotics is crucial to save the patient's life. Treatment must be started as soon as plague is suspected, even before laboratory test results are available [1]. If treatment is not received within 24 hours of the onset of the first symptoms, the risk of death increases significantly [1]. Antibiotics used in treatment include ciprofloxacin, doxycycline, gentamicin, levofloxacin, moxifloxacin, and streptomycin. Patients may also require oxygen, intravenous fluids, and respiratory support [1].

When should you seek medical help?

It is essential to contact a doctor immediately if you develop symptoms of plague after exposure to fleas or rodents, or if you live in or have visited an area where plague is prevalent [1]. Early diagnosis and treatment are key to recovering from this serious disease. You can learn more about the history of the disease, its symptoms, and methods of prevention and treatment by visiting Plague: History, Symptoms, Prevention, and Treatment (Arabic).

Medical references

• Plague
• About Plague