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Plague differs from many common infectious diseases in both its exposure routes and its warning signs. Bubonic plague typically follows an infected flea bite and causes painful swollen lymph nodes; pneumonic plague affects the lungs and can spread between people through close contact; septicemic plague infects the bloodstream. Fever, cough, and weakness overlap with many illnesses, so symptoms alone cannot confirm plague. If you have compatible symptoms and possible exposure to fleas, infected animals, or a plague-endemic area, seek urgent medical care.
How the three forms of plague differ
Plague is caused by the bacterium Yersinia pestis. Its symptoms depend in part on where infection takes hold, and its transmission risk differs by clinical form. [WHO; CDC]
Bubonic plague: painful swollen lymph nodes
Bubonic plague often follows a bite from an infected flea. Fever, chills, headache, and weakness may occur alongside one or more painful, swollen lymph nodes, called buboes. Person-to-person spread of bubonic plague is rare. [WHO; CDC; CDC]
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Pneumonic plague affects the lungs and can develop when plague spreads there from another form of the disease, or after a person inhales infectious respiratory particles from someone or an animal with pneumonic plague. Symptoms can include cough, shortness of breath, chest discomfort, and sometimes bloody sputum, along with fever and chills. This is the only plague form associated with person-to-person spread. CDC says that transmission typically requires direct, close contact with a person or animal with pneumonic plague. [WHO; CDC; CDC]
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Septicemic plague: infection in the bloodstream
Septicemic plague is a bloodstream infection. It can be the initial form of plague or develop after another form. Fever and chills can occur with severe weakness, abdominal pain, shock, bleeding, and tissue injury. [WHO; CDC]
How plague transmission compares with respiratory infections
Plague is a zoonotic disease: people can be exposed through infected fleas, contact with infected animal tissue or fluids, or inhalation of infectious particles from pneumonic plague. This is not the same exposure pattern as ordinary respiratory infections such as influenza. Pneumonic plague can spread between people, but CDC describes transmission as typically requiring direct and close contact with an infected person or animal. [CDC]
Influenza can also cause pneumonia, so cough, breathlessness, or other lung symptoms do not by themselves distinguish influenza from pneumonic plague. WHO operational guidance lists influenza-virus pneumonia as one differential diagnosis for pneumonic plague; that is an example, not a complete list of possible causes. [WHO operational guidance]
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How plague compares with illnesses that cause swollen lymph nodes
Painful swollen lymph nodes can be a clue to bubonic plague when they occur with fever and a relevant flea, animal, or geographic exposure. They are not unique to plague. WHO operational guidance identifies streptococcal causes of acute lymphadenopathy among the conditions clinicians may consider as alternatives. Symptoms alone cannot establish which infection is responsible. [WHO operational guidance]
The comparison is therefore about patterns, not a home diagnostic test: a painful bubo plus a plausible exposure raises concern for plague, but other infections can produce overlapping signs. A clinician needs to assess the illness and exposure history.
Why exposure history and location matter
CDC advises considering plague when compatible illness occurs in someone who lives in or has recently traveled to the western United States or another plague-endemic area. WHO reports that most plague cases reported globally during 2019–2025 were in the Democratic Republic of the Congo and Madagascar. Those global reporting patterns do not determine an individual’s risk; local exposure and travel history matter. [CDC clinician guidance; WHO]
When to seek medical care
Seek immediate medical attention for symptoms compatible with plague—especially fever with painful swollen lymph nodes, or a rapidly developing cough and breathing difficulty—if you may have had relevant flea, animal, or geographic exposure. Do not wait to see whether symptoms resolve or try to identify the disease from symptoms alone. CDC advises immediate medical attention for symptoms like those it lists for plague. [CDC]
Plague is serious, but early clinical assessment matters because it can be treated: WHO says antibiotic treatment is effective against plague bacteria and that early diagnosis and treatment can save lives. WHO’s 2026 fact sheet gives a 30%–60% case-fatality ratio for bubonic plague and a 30%–100% case-fatality ratio for plague left untreated; the latter is specifically an untreated-disease estimate, not a figure for treated cases. [WHO, 29 September 2026]
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How clinicians assess suspected plague
Symptoms and exposure history guide clinical assessment, but laboratory testing is used to investigate suspected plague. CDC lists blood and material from a swollen lymph gland among samples used for testing. If pneumonic plague is suspected, CDC clinical guidance calls for patient isolation and droplet precautions, and suspected cases should be reported promptly to local and state health departments. These are clinical and public-health measures, not instructions for people to manage a suspected case themselves. [CDC clinician guidance]
Reducing exposure in endemic areas
For reducing bubonic-plague exposure in endemic areas, WHO advises using insect repellent and avoiding contact with dead animals. These measures address flea bites and animal exposure; repellent does not treat an infection or prevent respiratory transmission from pneumonic plague. [WHO Q&A]
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