Recently, Northern Arizona recorded its first pneumonia-related death since 2007, following a similar incident in Oregon last year when the state saw its first bubonic plague case since 2015.
While the plague hasn’t been transmitted between people in the U.S. for over a century, sporadic cases do arise. But what leads to these occurrences?
Current plague cases in the United States are a far cry from those seen during the Middle Ages. Back then, the plague was responsible for the deaths of at least 25 million Europeans between 1347 and 1352.
Rats aboard ships from Crimea and Asia arriving in Sicily have long been blamed for introducing the bubonic plague to Europe. As fleas ran out of their rodent hosts, which lacked resistance, they sought humans as new hosts.
When someone is infected or potentially capable of spreading the plague, quarantine measures like those implemented during the COVID pandemic can be enacted. The development of vaccines in the late 19th century, improved sanitation, enhanced health practices, and modern antibiotics have all contributed to controlling the plague when it resurfaces.
Currently, the U.S. sees around seven cases of plague each year, according to the Centers for Disease Control and Prevention, while the World Health Organization notes that most human cases in the past three decades have occurred in Africa.
If cases arise in the U.S., they predominantly appear in the western states, particularly in New Mexico and Arizona, with some also reported in southern Oregon, western Nevada, and California.
Plague cases generally tend to be glandular in nature.
Plague manifests in three primary forms: bubonic (the one historically associated with the Black Death), septicemic, and pneumonic. All forms are attributed to the Yersinia pestis bacterium, which affects both humans and mammals.
Each type of plague presents distinct symptoms and is caused by varying factors.
Bubonic plague results from flea bites, especially from rodents, and is characterized by a sudden high fever, chills, headaches, abdominal pain, and swollen lymph nodes that may ooze pus. The bacteria can proliferate within the lymph nodes and potentially spread throughout the body if not treated with antibiotics.
Septicemic plague has similar symptoms, including fever, chills, extreme fatigue, abdominal distress, and possibly bleeding from the skin or internal organs. This form can emerge from untreated bubonic plague or through contact with infected animals.
If someone with glandular or septic plague doesn’t receive treatment and the bacteria infects their lungs, they may develop pneumonia. Individuals can also contract pneumonic plague by inhaling droplets expelled by infected people or animals. Common symptoms include fever, headache, weakness, and accelerated pneumonia onset.
The incubation period for bubonic and septic plague typically spans several days, whereas pneumonia can manifest in over a day. Notably, pneumonic plague is the only variant known to spread directly between people and is considered the most dangerous.
From 2020 to 2023, the CDC reported 15 cases of plague in humans, with three casualties. According to the Cleveland Clinic, effective treatment requires antibiotics as soon as possible. Administering antibiotics within 24 hours of the onset of symptoms significantly enhances recovery likelihood, with many feeling better within a week or two.
Generally, around 90% of patients survive with prompt treatment. However, without intervention, the plague can be fatal.
Health officials have not disclosed how the Arizona resident, who succumbed to the pneumonia plague earlier this year, contracted the disease. The previous year’s case in Oregon was linked to a pet cat. In recent years, Colorado has reported positive tests for septic plague in cats, as well as in prairie dog colonies and squirrels.
Infectious fleas are the primary source of plague cases in the U.S. today, but handling infected animals—such as cats, rabbits, and rodents—can also pose risks.
To minimize the risk of infection, it’s advisable to take precautions against flea bites. This includes using insect repellent containing DEET and keeping outdoor areas clean to deter fleas. Moreover, it’s essential to speak with veterinarians about flea prevention for pets, particularly if they live in areas prone to the plague.
