Plague Symptoms, Treatment, and Infection Prevention

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What is Plague? 

Plague is a serious bacterial infection. There are five forms of plague: bubonic, pneumonic, septicemic, meningeal and pharyngeal. 

It is found primarily in semi-arid forests and grasslands and most commonly affects animals such as squirrels, voles, rabbits, and prairie dogs. Carnivores can also be infected if they consume infected prey. Pets, particularly cats, are also at risk of contracting Y. pestis in these regions. 

How do Humans Become Infected? 

The bacteria that cause plague, Yersinia pestis, is transmitted to humans who are bitten by fleas that have fed on infected animals, by handling infected animals, or inhalation of infected respiratory droplets. 

Most human cases of plague in the United States occur in northern New Mexico, northern Arizona, southern Colorado, California, southern Oregon, and western Nevada. Globally, plague epidemics have occurred in South America, Asia, and Africa, where recent epidemics have occurred in smaller villages or towns. 

Pneumonic plague is the only form of plague that can be transmitted person-to-person. It requires close, sustained contact in order to spread. In fact, there hasn’t been a case of person-to-person transmission of pneumonic plague documented in the U.S. since 1924. (CDC) 

Is Plague Deadly? 

In the Middle Ages, plague was responsible for the death of an estimated 50 million people, or 60 percent of Europe’s population at the time. However today there are fewer than 5,000 cases of plague a year, and in the U.S. there have been an average of just 7 cases of plague a year in recent decades. 

Prior to the development of sulfonamide antibiotics, the mortality for all plague infections was between 66-93 percent. Modern antibiotics are effective at treating the plague, but plague infections can cause death if they are not identified and treated promptly. 

How to Diagnose Plague

Health care practitioners should consider a plague diagnosis if a patient has symptoms suggestive of plague and lives in or has recently traveled to the western United States or other areas where plague is endemic.  

Signs and symptoms of plague vary depending on the type of plague. Of the five forms of plague, bubonic, pneumonic, and septicemic plague are the most common.  

• The characteristics of bubonic plague include swollen, tender lymph nodes (i.e., “bubo”) near the site of a flea bite, fever, chills, malaise, and headache. Symptoms onset 2-8 days after exposure. 
• Pneumonic plague is characterized by fever, shortness of breath, cough with purulent or bloody sputum. A chest X-ray (CXR) often looks “worse” than the patient early on in course. Symptoms typically start within 1-3 days. 
• Septicemic plague is identified by fever, chills, extreme weakness, abdominal pain, shock, and possibly bleeding into the skin and other organs. Skin and other tissues may turn black and die, especially on fingers, toes, and the nose. Symptom onset is not clearly defined, but likely happens within days. 

Blood or samples of a swollen lymph gland can be tested to determine the cause of illness, however if plague has been identified as a possible cause of illness, treatment should begin immediately. 

Type	Risk Factors	Characteristics
Bubonic plague (most common)	Bite from infected fleas, most commonly the Oriental rat flea (Xenopsylla cheopsis)	Swollen, tender lymph nodes (i.e. “bubo”) near the site of a flea bite  Fever, chills, malaise, headache  Symptoms onset 2-8 days after exposure
Pneumonic plague	Inhaled through infectious respiratory droplets from a sick animal or human	Fever, shortness of breath, cough with purulent or bloody sputum  Chest X-ray (CXR)  often looks “worse” than the patient early on in course  Bilateral pulmonary infiltrates often present  Symptoms onset 1-3 days after exposure
Septicemic plague		Fever and sepsis without localizing symptoms. Abdominal pain, nausea, vomiting, or diarrhea may be present  Delays in diagnosis are often present
Meningeal plague	Recent infection with bubonic, pneumonic, or septicemic plague	ever, stiff neck, and confusion  Present in 6% of individuals with plague.   Symptom onset 9-14 days after onset of acute plague infection
Pharyngeal plague	Contamination of the oropharynx with Y. pestis-infected materials such as inadequately cooked meat of infected animals.	Sore throat with or without swollen lymph nodes in the neck

How do You Treat Plague? 

Prompt treatment is critical to prevent complications or death. Two classes of antibiotics are recommended for the initial treatment for Y. pestis infection, at least one of which is considered first-line. See the CDC’s recommendations for the antimicrobial treatment and prophylaxis of plague resulting from either naturally occurring transmission or a bioterrorism-related event (Tables 1-3, 5, 7, 8). The use of two antibiotics is recommended to minimize the chance that the patient receives ineffective therapy.  

There is little antibiotic resistance that naturally occurs in Y. pestis, although engineered strains of Y. pestis associated with bioterrorism could be substantially resistant. Once susceptibility information is available, most clinicians narrow antibiotics to just one effective agent.  

PPE and Infection Prevention Control 

Y. pestis is transmitted through larger exhaled water particles and remains suspended for a short duration of time. While standard precautions are used for all patients, droplet precautions, meaning use of a medical mask, are also utilized for patients with suspected or confirmed pneumonic plague.  

Transmission is highest when a patient is in the mid- to late-stages of infection, when patients are both coughing vigorously and have large amounts of bacteria present in their lungs. Droplet precautions may be removed once a patient has had effective antibiotics for at least 48 hours, clinical improvement is seen, and sputum production has decreased. 

Post-Exposure Prophylaxis for Plague 

Risk determination for health care workers should be assessed in collaboration with the Infection Prevention and Control Department and the Occupational Health team (at the facility?). Antibiotics can be offered as post-exposure prophylaxis to individuals who were not wearing a mask and had close prolonged contact with a patient with pneumonic plague. Laboratory workers who handled Y. pestis specimens without proper precautions should also be offered prophylactic antibiotics. Finally, antibiotics are also offered to anyone who has been in contact with an infected animal. Antibiotics are generally given for 7 days in the event of exposure (see Table 4, 6, and 9, CDC).