While many associate plague with medieval times and the infamous Black Death, a recent death in northern Arizona has underscored the persistent threat of this flea-borne disease, even in modern America. Health authorities in Coconino County, which encompasses Flagstaff, confirmed that an individual succumbed to pneumonic plague, a severe respiratory infection caused by the bacterium Yersinia pestis.
In the United States, incidents of human plague are quite uncommon. The Centers for Disease Control and Prevention (CDC) reports an average of seven human cases each year. Before this incident in Arizona, the latest fatality occurred in 2021. Y. pestis first appeared in American port cities around 1900 and has since established itself among rodent populations in several western states, including New Mexico, Arizona, Colorado, California, Oregon, and Nevada.
David Wagner, the executive director of the Pathogen and Microbiome Institute at Northern Arizona University and a plague researcher for over 25 years, emphasizes the rarity of plague in the U.S., suggesting that everyday precautions like wearing a seatbelt are more critical for safety. However, the recent fatal case highlights the ongoing need for vigilance against this ancient disease.
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In a conversation with *Scientific American*, Wagner discussed how plague operates, its symptoms, and why it continues to persist.
**How does plague infect individuals?**
Plague primarily affects rodents and their fleas. An infected rodent is bitten by a flea, which then carries *Y. pestis*. When this flea bites another rodent, it transmits the bacterium, perpetuating a cycle among rodent populations. This cycle has maintained the plague in natural environments for millennia.
**What’s the difference between bubonic and pneumonic plague?**
Plague, known historically as the Black Death, manifests in different forms. The recent case in Arizona involved pneumonic plague, which is particularly rare in the U.S. Most human cases derive from the bite of an infected flea. If no suitable rodent host is available, the flea might bite a human, transmitting the disease.
If the body’s immune defenses don’t halt *Y. pestis* at the entry point, the bacterium travels through the lymphatic system to the nearest major lymph node, causing it to swell (a condition known as a bubo, hence bubonic plague). Without flea-to-human transmission, the disease typically ends with the treatment or death of the infected person.
Untreated, bubonic plague can progress to the lungs, becoming secondary pneumonic plague, which can then be spread from person to person, termed primary pneumonic plague. Pneumonic plague can also arise from close contact with an infected animal.
**Can pets transmit plague?**
While it’s rare, pets, particularly those that roam freely, might carry fleas from infected rodents into human living spaces. Protective measures like flea and tick collars are advisable. Dogs often resist the infection and can develop antibodies, but cats are more vulnerable and can progress rapidly to pneumonic plague, posing a risk to humans.
**Symptoms and Treatment**
Typical symptoms of bubonic plague include fever, headache, chills, fatigue, and swollen lymph nodes. The disease is treatable with various antibiotics if diagnosed promptly. Left untreated, bubonic plague can be fatal in 30 to 60 percent of cases, while untreated pneumonic plague is nearly always fatal. Diagnosis can be challenging as symptoms resemble those of other illnesses, making rapid laboratory testing crucial.
**Plague Distribution and Endurance**
Plague has been endemic in western U.S. rodent populations for over a century, likely due to similarities between native rodents and those in Central Asia, where the bacterium originated. It spread rapidly across the western states but halted unexpectedly at the edge of the Great Plains. Wagner is currently collaborating with researchers in Madagascar, which reports more human plague cases annually than any other country.
**Long-term Persistence and Diminished Threat**
The lethality of plague has decreased over time, with historical pandemics claiming millions of lives. Today, improved hygiene helps control rat populations in urban areas, and the availability of antibiotics prevents large-scale outbreaks. Despite its persistence in certain environments, our understanding and ability to manage plague have significantly reduced its threat to public health.
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Cameron Aldridge combines a scientific mind with a knack for storytelling. Passionate about discoveries and breakthroughs, Cameron unravels complex scientific advancements in a way that’s both informative and entertaining.