Pneumonic plague is the most severe form of plague, caused by the bacterium Yersinia pestis. It affects the lungs and can spread quickly, making early diagnosis and treatment critical. Unlike other forms of plague, pneumonic plague can be transmitted from person to person through respiratory droplets.
The disease typically begins with mild or nonspecific symptoms, such as fever and headache, and rapidly progresses to severe pneumonia, often with coughing up blood. Without prompt treatment, the condition can lead to respiratory failure and death within 18 to 36 hours. Although rare in the US, it remains a public health concern due to its high fatality rate and potential for outbreaks.
Effective treatment is available with antibiotics, especially if started early. Prevention includes avoiding contact with infected people or animals, using protective measures in high-risk areas, and receiving post-exposure antibiotics if exposed. Surveillance and rapid response systems are essential to contain potential outbreaks.
Main symptoms
Pneumonic plague usually starts 1 to 3 days after exposure, with a sudden onset of fever, chills, headache, and weakness. These symptoms are often mistaken for other respiratory infections.
As the disease progresses, more specific symptoms appear, including shortness of breath, chest pain, and a worsening cough. The most characteristic symptom is a severe cough producing bloody or watery sputum (hemoptysis), which increases as the illness advances.
If left untreated, the disease can rapidly lead to respiratory failure, septic shock, and death, often within 18 to 36 hours from the onset of symptoms.
Confirming a diagnosis
Because initial symptoms are nonspecific, laboratory testing is essential for diagnosis. The most reliable test is a culture of sputum, blood, or lymph node aspirates to identify Yersinia pestis.
Rapid diagnostic tools, like the F1 antigen rapid diagnostic test (F1RDT), are useful for early detection, especially in areas with limited resources. However, while F1RDT has high sensitivity, its specificity is lower than standard cultures.
Chest X-rays often show bilateral pneumonia or pleural effusion, though these findings are not unique to pneumonic plague. Imaging helps support the diagnosis alongside clinical and lab findings.
How it’s transmitted
Pneumonic plague is the only form of plague that spreads directly from person to person. Transmission occurs when an infected person coughs or sneezes, releasing droplets that others inhale.
Close contact (within 6 feet) is usually required, and people are most contagious during the later stages of illness when they produce large amounts of bloody sputum.
Transmission from animals is also possible. Domestic cats infected with plague have been known to transmit the disease to humans. Handling infected corpses or carcasses may also pose a risk, though this is less common.
Common causes
Pneumonic plague is caused by infection with Yersinia pestis, a gram-negative bacterium that evolved from a milder ancestor, Y. pseudotuberculosis.
Infection can result from inhaling airborne bacteria during close contact with an infected person or animal. It can also develop when bubonic or septicemic plague spreads to the lungs through the bloodstream.
Environmental exposure in endemic areas, especially in contact with rodents or their fleas, increases the risk of infection. Although rare, plague is still found in parts of the western US.
Treatment options
Early antibiotic treatment is critical to reduce the risk of death. First-line antibiotics include fluoroquinolones such as levofloxacin and moxifloxacin, both approved by the FDA for plague treatment.
Aminoglycosides like streptomycin and gentamicin are also effective. Doxycycline and chloramphenicol serve as alternatives, especially when intravenous treatment is unavailable.
Treatment usually lasts 10 to 14 days. Patients often begin with injectable antibiotics and switch to oral forms once they improve. In cases involving possible antibiotic resistance, combination therapy with drugs from different classes is recommended.
How to prevent
Prevention focuses on avoiding exposure to the bacteria. This includes staying away from infected individuals or animals, especially in areas where plague is endemic.
Protective steps include using insect repellent to avoid flea bites, wearing gloves and masks when handling animals, and limiting contact with people showing respiratory symptoms.
Rodent control is essential. Keeping homes and workplaces clear of food waste, sealing entry points, and restricting pet access to outdoor areas in affected regions can help reduce risk.
Post-exposure care and isolation
People exposed to pneumonic plague should receive post-exposure antibiotics, usually doxycycline for 7 days following their last exposure. This reduces the chance of developing symptoms.
Patients diagnosed or suspected to have pneumonic plague must be isolated for at least 72 hours after starting treatment. Health workers should follow droplet precautions, using masks and eye protection.
Is there a vaccine?
Currently, there is no approved vaccine for pneumonic plague in the US. However, several vaccines are under development, including subunit vaccines and live attenuated options.
Research aims to create vaccines that stimulate both antibody and cellular immune responses. Some experimental vaccines have shown promise in animal studies, but none are commercially available yet.