The plague: Infectious disease caused by the bite of a flea or infected rat

The plague is a contagious epidemic disease caused by the plague bacillus Yersinia pestis, (a bacterium) transmitted by the rat flea, which jumps to humans after the death of the rat (by plague). The symptoms of plague depend on the route of exposure to the plague bacteria. Plague may take several clinical forms, but the most common are bubonic plague, pneumonic plague, and plague sepsis. The plague is a very serious disease, but it is generally treatable with antibiotics. Prompt treatment increases the chances of a full recovery.

  • Synonyms of the plague
  • Infectious disease epidemiology
  • Causes: Bite from flea or infected rat
  • Symptoms and types: Bubonic plague, pneumonic plague and plague sepsis
  • Diagnosis and examinations
  • Therapy
  • Prevention

Synonyms of the plague

The plague is also known by these synonyms:

  • pestis
  • Black Death

Infectious disease epidemiology

Sporadic cases of plague (and occasional epidemics) occur worldwide. Every year, the World Health Organization reports hundreds of new patients with the disease, with a mortality rate of 10-30%. The majority of plague patients live in South Africa, although the disease occasionally occurs in developed countries among people who engage in extensive outdoor activities. Furthermore, the plague has no sexual preference. Finally, most patients with the plague are younger than twenty years old.

Causes: Bite from flea or infected rat

Yersinia pestis (old name Pasteurella pestis ) is a gram-negative bacillus (bacterium) that causes plague. The main hosts are forest rodents, which transmit the infection to domestic rats (Rattus rattus). The usual vector is the rat flea Xenopsylla cheopis . These fleas bite humans when there is a sudden decrease in the rat population. Working with rat carcasses is also a risk factor for contracting the plague. Occasionally, the spread of the organisms occurs through contaminated feces entering skin wounds or through droplet infection.

Symptoms and types: Bubonic plague, pneumonic plague and plague sepsis

Three clinical forms of the plague are best known: bubonic plague, pneumonic plague and plague sepsis. General symptoms of the disease include sudden onset of fever, headache, morning headache, chills, body aches, weakness, vomiting, nausea, delirium (acute confusion with changes in brain function), and other toxic signs.

Bubonic plague

Bubonic plague is also known as bubonic or bubonic plague. This is the most common form of plague and occurs in approximately 90% of infected individuals. Infection occurs through direct contact with the plague bacillus. The incubation period (time between contracting the infection and the appearance of symptoms) is two to seven days. The onset of the disease is acute, with a patient suddenly developing high fever, chills, headache, muscle pain, nausea, vomiting, weakness and severe fatigue. This is quickly followed by lymphadenopathy, a condition in which very painful swellings of the glands occur, usually in the groin area. Bleeding under the skin may also occur (pestis haemorrhagica, black plague). If left untreated, death occurs in 50 to 90% of cases within two to five days of the onset of symptoms. The treated form of bubonic plague has a mortality of 10 to 20%.

Pneumonic plague

Characteristic of pneumonic plague (pestis pulmonum) is the abrupt onset of symptoms with life-threatening pneumonia accompanied by bloody phlegm. The patient has respiratory distress and cyanosis (a blue discoloration of the skin and mucous membranes), and therefore always dies if he does not receive treatment. In half of the cases, the patient survives if the doctor treats him in time with antibiotics.

Plague sepsis

Plague sepsis occurs as the first symptom of plague, or develops as a result of untreated bubonic plague. This form is the result of bites from infected fleas or working with an infected animal. Plague sepsis presents as an acute fulminant (severe) infection with signs of shock and disseminated intravascular coagulation (bleeding into the skin and other organs). Patients with this form of the plague also develop fever, chills, extreme weakness, abdominal pain and shock. The skin and other tissues turn black and die. The fingers, toes and nose are especially sensitive to this. Swollen lymph nodes are rare in this type of plague. About one in four to one in five patients die from plague sepsis.

Diagnosis and examinations

Physical and diagnostic examination

The diagnosis of plague is based on clinical and epidemiological findings and laboratory results. Microscopy of the blood or lymphatic fluid is necessary to confirm the diagnosis.

Differential diagnosis

The doctor may confuse the plague with the following conditions because the clinical picture is similar:

  • bacterial pharyngitis (strep throat)
  • bacterial sepsis
  • brucellosis (bacterial infection with flu-like symptoms)
  • cellulitis (skin infection with painful, red and swollen skin)
  • cat scratch disease (skin lesions and swollen lymph nodes)
  • diffuse intravascular coagulation
  • tonsillitis (tonsillitis) and a peritonsillar abscess (abscess around the tonsils)
  • a bacterial pneumonia
  • a B-cell lymphoma
  • septic shock (complication of sepsis with low blood pressure)
  • a sore throat (bacterial infection with genital ulcers)
  • dengue fever (dengue: viral infection)
  • lymphadenitis (inflammation of the lymph nodes)
  • lymphadenopathy
  • lymphogranuloma venereum (swelling of the lymph nodes and genitals)
  • malaria
  • anthrax
  • pasteurella multocida infection (bacterial infection with wound infections and damage to other body structures)
  • Rocky Mountain spotted fever (tick-borne disease with fever, headache and rash)
  • syphilis (bacterial infection acquired through sexual contact)
  • tularemia (bacterial infection due to infected wild animals)
  • typhoid (bacterial infection due to infected insect bite)


The doctor quickly initiates the treatment of the plague; In other words, he does not wait for the research results. The preferred treatment consists of an antibiotic that the doctor administers intramuscularly (into the muscles) to the patient. The patient receives this three times a day for ten days. Furthermore, oral medication (taken by mouth) is also effective. Patients with pneumonic plague are isolated in hospital during treatment because this form is highly contagious.


Plague prevention is done by eliminating the flea population. Outbuildings or cabins should be sprayed with insecticides effective against local fleas.