Plague

Primary reference(s)

WHO 2022. Plague. World Health Organization (WHO). Accessed 25 May 2025.

Annotations

Key relevant UN convention / multilateral treaty

International Health Regulations (2005), 3rd ed. (WHO, 2016).

Drivers

Plague is transmitted between animals and humans by the bite of infected fleas, direct contact with infected tissues, and inhalation of infected respiratory droplets.

Humans can be infected through the bite of infected vector fleas, unprotected contact with infectious bodily fluids or contaminated materials, and the inhalation of respiratory droplets/small particles from a patient with pneumonic plague (WHO, 2022).

Impacts

People infected with plague usually develop acute febrile disease with other non-specific systemic symptoms after an incubation period of one to seven days, such as sudden onset of fever, chills, head and body aches, and weakness, vomiting and nausea (WHO, 2022). 

There are two main forms of plague infection, depending on the route of infection: bubonic and pneumonic. 

• Bubonic plague is the most common form of plague and is caused by the bite of an infected flea. Plague bacillus, Y. pestis, enters at the bite and travels through the lymphatic system to the nearest lymph node where it replicates itself. The lymph node then becomes inflamed, tense and painful, and is called a ‘bubo’. At advanced stages of the infection the inflamed lymph nodes can turn into open sores filled with pus. Human-to-human transmission of bubonic plague is rare. Bubonic plague can advance and spread to the lungs, which is the more severe type of plague called pneumonic plague.
• Pneumonic plague, or lung-based plague, is the most virulent form of plague. Incubation can be as short as 24 hours. Any person with pneumonic plague may transmit the disease via droplets to other humans. Untreated pneumonic plague, if not diagnosed and treated early, can be fatal. However, recovery rates are high if detected and treated in time (within 24 hours of onset of symptoms) (WHO, 2022).

Multi-hazard context

Over the past several hundred years, there have been three pandemics with high mortality rates (Jedwab, et al, 2021). It has been absent from Europe for more than 50 years but continues to affect the Americas, Africa and Asia. Plague is infamous for killing millions of people in Europe during the Middle Ages. People at the highest risk are those in contact with wild rodents and fleas in plague-affected areas, and travellers in high-risk areas. Plague is mainly found in rodents and transmission between rodents and humans is usually via fleas. Although human-to-human transmission is rare in the case of bubonic plague, in cases of pneumonic plague it occurs after inhalation of infectious droplets from infected persons. The main control measures are to reduce contact with wild rodents and their fleas and to establish surveillance and control programmes in risk areas (ECDC, no date). 

Managing exclusionary policies where local communities are purposely or unintendedly excluded from decision and action processes contributes to inefficiency in the disease control policies adopted by authorities, especially if it causes distrust in the government, or if it spurs conflict between groups (Jedwab et al., 2021).

Risk Management

Antibiotic treatment is effective against plague bacteria, so early diagnosis and early treatment can save lives (WHO, 2022). WHO does not recommend vaccination, except for high-risk groups (such as laboratory personnel who are constantly exposed to the risk of contamination, and health-care workers) (WHO, 2022). 

For managing plague outbreaks, WHO recommends the following:  

• Find and stop the source of infection. Identify the most likely source of infection in the area where the human case(s) was exposed, typically looking for clustered areas with large numbers of small animal deaths. Institute appropriate infection, prevention and control procedures. Institute vector control, then rodent control. Killing rodents before vectors will cause the fleas to jump to new hosts, this is to be avoided.
• Protect health workers. Inform and train them on infection prevention and control. Workers in direct contact with pneumonic plague patients must wear standard precautions and receive a chemoprophylaxis with antibiotics for the duration of seven days or at least as long as they are exposed to infected patients.
• Ensure correct treatment: Verify that patients are being given appropriate antibiotic treatment and that local supplies of antibiotics are adequate.
• Isolate patients with pneumonic plague. Patients should be isolated so as not to infect others via air droplets. Providing masks for pneumonic patients can reduce spread.
• Surveillance: identify and monitor close contacts of pneumonic plague patients and give them a seven-day chemoprophylaxis. Chemoprophylaxis should also be given to household members of bubonic plague patients.
• Obtain specimens which should be carefully collected using appropriate infection, prevention and control procedures and sent to labs for testing.
• Disinfection. Routine handwashing is recommended with soap and water or use of alcohol hand rub. Larger areas can be disinfected using 10% of diluted household bleach (made fresh daily).
• Ensure safe burial practices. Spraying of the face/chest area of suspected pneumonic plague deaths should be discouraged. The area should be covered with a disinfectant-soaked cloth or absorbent material (WHO, 2022). 

Preventive measures include informing people when zoonotic plague is present in their environment and advising them to take precautions against flea bites and not to handle animal carcasses. Generally, people should be advised to avoid direct contact with infected body fluids and tissues. When handling potentially infected patients and collecting specimens, standard precautions should apply (WHO, 2022). 

Surveillance and control require investigating animal and flea species implicated in the plague cycle in the region and developing environmental management programmes to understand the natural zoonosis of the disease cycle and to limit spread. Active long-term surveillance of animal foci, coupled with a rapid response during animal outbreaks has successfully reduced numbers of human plague outbreaks (WHO, 2022).

Monitoring

WHO supports countries to conduct all-hazards strategic risk assessment in the contexts of health emergencies and disasters, which results in the development of a country risk profile. Empowered with the country risk profile, inclusive of a seasonal risk calendar, countries can anticipate potential emergencies before they occur to trigger early alerts and inform early actions (WHO, 2021a; b).

WHO's Early Warning, Alert and Response System (EWARS) has been designed to improve disease outbreak detection in emergency settings, such as in countries in conflict or following a natural disaster. It is a simple and cost-effective way to rapidly set up a disease surveillance system. EWARS is deployed during an emergency as an adjunct to the national disease surveillance system. WHO works with Ministries of Health and health sector partners to train local health workers to use the system. After the emergency, EWARS should re-integrate back into the national system (WHO, no date)

In order to effectively and efficiently manage plague outbreaks it is crucial to have a robust surveillance system and an informed and vigilant health-care workforce (and community) to quickly diagnose and manage patients with infection, identify risk factors, conduct ongoing surveillance, control vectors and hosts, confirm diagnosis with laboratory tests, and to communicate findings with appropriate authorities (WHO, 2022).

A robust surveillance system is the key to the early warning of plague occurrences or outbreaks. This is related to a favourable outcome due to early case detection and treatment, in addition to leading to a more accurate quantification of the disease burden and geographical distribution. The plague surveillance should ideally include a combination of human, animal and climate surveillance. The surveillance system should be adapted based upon the scenario, season and early warning signs. For example, a community-based surveillance system has been used in Madagascar to strengthen early warning systems for plague (Ratsitorahina, 2000).