[Edaily Reporter NA EUN-KYUNG ] Although the plague is often thought of as a disease that disappeared along with the Middle Ages, it still circulates among wild rodents and fleas today. According to the World Health Organization (WHO), 3,847 suspected cases and 423 deaths were reported across 10 countries between 2019 and 2025. To respond to naturally occurring infections, research institutions around the world are using the plague bacterium to develop diagnostic methods, vaccines, and treatments, while also preparing for the possibility of bioterrorism.

Recently, local reports emerged that an employee at the Irkutsk Anti-Plague Research Institute in Russia died of pneumonia of unknown origin after breaking a test tube containing the plague bacterium, which led to infection. Russian authorities have denied that the death was caused by a laboratory accident or plague infection. Although more than 5,000 tests were conducted on contacts and others, no additional confirmed cases or related patients with severe pneumonia were identified, and the preventive quarantine measures were lifted on the 8th. However, the WHO states that the cause of death remains undetermined and has requested additional data from Russian authorities.

When the infection becomes severe, the plague can cause bleeding under the skin and circulatory failure, leading to black necrosis of tissues in the hands, feet, and other areas; for this reason, it was historically known as the “Black Death.” It is an acute infectious disease caused by the bacterium “Yersinia pestis.”

In nature, infection primarily occurs when fleas—which have fed on the blood of wild rodents such as rats and marmots infected with the plague bacterium—bite humans. When rodents die from the plague, the fleas may seek new hosts and transfer the infection to humans or pets. The bacteria can also enter the body through wounds sustained while handling the carcasses of infected animals or during the process of skinning them; bodily fluids or respiratory secretions from infected cats can also serve as sources of infection. When infection occurs in this manner, it typically begins as the lymph node form, but if the bacteria spread to the bloodstream or lungs, it can progress to the septicemic or pneumonic forms. In rare cases, human-to-human transmission can occur when respiratory droplets from a patient with the pneumonic form are inhaled at close range. In South Korea, it is classified as a Class 1 notifiable infectious disease, meaning any confirmed or suspected cases must be reported immediately.

The reason the plague is so feared is that it has a high fatality rate when left untreated and progresses rapidly. According to the WHO, the fatality rate for untreated bubonic plague ranges from 30% to 60%, while the septicemic and pneumonic forms are virtually fatal if not treated early. In particular, the pneumonic form can lead to death within 18 to 24 hours after symptoms begin, so antibiotics must be administered without waiting for test results.

The most common form, bubonic plague, is characterized by sudden high fever, chills, headache, and muscle aches, along with swollen and extremely painful lymph nodes in the groin, armpits, or neck. The septicemic form, in which the bacteria spread into the bloodstream, can cause abdominal pain, vomiting, shock, subcutaneous bleeding, and tissue necrosis. The pneumonic form, which affects the lungs, rapidly causes shortness of breath, chest pain, coughing, and bloody sputum. While the lymphadenitic form generally does not spread easily from person to person, the pneumonic form can be transmitted to others through respiratory droplets from an infected person.

Antibiotics used to treat plague include streptomycin, gentamicin, doxycycline, and ciprofloxacin, levofloxacin, and moxifloxacin. The choice of medication and route of administration depends on the patient’s age, severity of symptoms, kidney function, and drug susceptibility; the typical treatment duration is 10 to 14 days.

Medications approved in Korea for the treatment of plague include Youngpoong Pharmaceutical’s “Youngpoong Doxycycline Tablets 100 mg” (active ingredient: doxycycline). Doxycycline inhibits the proliferation of Yersinia pestis by interfering with its protein synthesis. Other domestically available products containing active ingredients used to treat plague include “Kravit Tablets” ( JEIL PHARM(271980), containing levofloxacin), “Ciproby Tablets” (Bayer Korea, containing ciprofloxacin), and “Avelox Tablets and Injectable Solution” (Bayer Korea, containing moxifloxacin).

A notable aspect of developing treatments for plague is that conducting standard clinical trials to verify efficacy in humans is virtually impossible. This is because it is not possible to intentionally infect healthy people with the plague bacterium to assess therapeutic effects, and the low number of naturally occurring cases makes it difficult to conduct large-scale clinical trials.

The U.S. Food and Drug Administration (FDA) applies the “Animal Rule” to such infectious diseases. This is a system that allows for the approval of a drug if therapeutic effects—such as improved survival rates—are confirmed in animal studies and safety and pharmacokinetic data are obtained from human studies. Through this process, Janssen’s “Levquin” (levofloxacin) received FDA approval in 2012, and Bayer’s “Cipro” (ciprofloxacin) and “Avelox” (moxifloxacin) received approval in 2015 as treatments for pneumonic and septicemic plague, as well as for post-exposure prophylaxis. Since existing antibiotics are effective, there are currently no separate targeted therapies or approved antibody treatments specifically designed to target the plague bacterium.

Prevention is also possible. In areas where plague is endemic, use repellents to avoid flea bites and avoid contact with wild rodents or the carcasses of dead animals. If you have had sustained close contact with a patient with pneumonic plague or have been directly exposed to infected bodily fluids or tissues, you may take doxycycline or a fluoroquinolone antibiotic prophylactically for 7 days, as determined by a healthcare professional.

There is currently no plague vaccine available for the general public. The WHO also does not recommend vaccination except for high-risk groups, such as researchers and healthcare workers who may be repeatedly exposed to the plague bacterium. Currently, U.S.-based Dynavax Technologies and the Department of Defense are developing the plague vaccine candidate “rF1V-1018” in Phase 2 clinical trials, but it has not yet reached the approval stage.

Plague is not a disease for which there is no treatment; rather, it becomes dangerous if treatment is delayed. If you experience sudden high fever, severe pain accompanied by swollen lymph nodes, shortness of breath, or bloody sputum within 1 to 7 days after traveling to an epidemic area or coming into contact with an infected animal, you should seek medical attention immediately and inform the healthcare provider of your travel history and any potential exposure.