Just in time for Halloween, and centuries after “the black death” was the most feared thing in the world, new reports that one or more Russian scientists may have died from plague, possibly the pneumonic form, have once again put this ancient killer in the news. People are, well, justifiably concerned. Could this turn into another COVID? Is “the black death” back?
The answer is, “it’s complicated.”
Let’s Look at the Science
Whatever is going on in Russia is hardly comforting, but we’ll leave the speculation to others. Instead, let’s look at the science.
As The American Council on Science and Health reports, what we think of as “the plague” can take several forms. Bubonic plague is the one everybody knows, complete with its grotesquely swollen lymph nodes, or buboes. But pneumonic plague is even worse. Once Yersinia pestis infects the lungs, the disease can progress with terrifying speed, causing severe pneumonia, respiratory failure, and sometimes bloody sputum. Untreated, death can follow within days.
Laboratory exposure to plague is not unprecedented. Of more than 1,000 plague cases reported in the United States, 27 resulted from occupational exposure, including five infections in laboratory researchers. The most recent U.S. laboratory-acquired infection occurred in 2009 and was fatal. Plague vaccines are available outside the United States, although none is currently licensed here. Where they are available, vaccination is generally recommended only for people at high risk of exposure, including researchers who work with Y. pestis.
The Plague, Then
According to the Centers for Disease Control and Prevention (CDC), Plague was first introduced into the United States in 1900, from rat–infested steamships that had sailed from affected areas. Epidemics occurred in port cities. The last urban plague epidemic in the United States occurred in Los Angeles from 1924 through 1925. Plague then spread from urban rats to rural rodent species and became entrenched in many areas of the western United States. Since that time, plague has occurred as scattered cases in rural areas. Most human cases in the United States are acquired in two regions:
- Northern New Mexico, northern Arizona, and southern Colorado
- California, southern Oregon, and far western Nevada
Over 80% of United States plague cases have been the bubonic form. In recent decades, an average of five human plague cases have been reported each year (range: 0–17 cases per year). Plague has occurred in people of all ages (infants up to age 96), though 50% of cases occur in people ages 12–45. It occurs in both men and women, though historically is slightly more common among men, probably because of increased outdoor activities that put them at higher risk.
Meet Yersinia Pestis
Yersinia pestis, commonly known as “pneumonic plague,” is an extraordinarily virulent bacterium whose natural ecology involves rodents and the fleas that feed on them. Infected fleas can transmit the bacterium to other rodents, other mammals, and humans. Some wild rodents can harbor Y. pestis without obvious illness, allowing the organism to persist in natural reservoirs.
Cats are particularly susceptible to plague and can become infected through contact with infected rodents. They can, in turn, transmit the infection to humans. Under certain circumstances, plague can also spread directly from person to person. That becomes especially important with pneumonic plague because respiratory droplets from an infected person can transmit the bacterium without requiring a flea at all.
The Plague, Now
This is where 2026 differs rather dramatically from 1348. Today, plague, and specifically Y. pestis, is treatable with antibiotics, but speed matters. Because delaying treatment can be fatal, physicians are advised to begin antibiotics when plague is strongly suspected rather than waiting for laboratory confirmation.
Several antibiotics are effective against Y. pestis. Ciprofloxacin and other fluoroquinolones are important options, and depending on the patient’s condition, they can be given orally or intravenously. Gentamicin is also widely used. Streptomycin, the classic plague antibiotic, remains effective but can be difficult to obtain. Treatment generally continues for about 10–14 days, depending on the drug and clinical circumstances.
Antibiotics have obviously changed the equation. Before their introduction, plague was extraordinarily lethal. In an analysis of U.S. plague cases from 1900 through 2012, 66 percent of patients died before antibiotics became available. After their introduction, mortality fell to 16 percent. More strikingly, among 377 patients with all forms of plague who received at least one dose of an effective antibiotic, 9 percent died, compared with 52 percent of those who received either no treatment or ineffective treatment.
But Treatable Doesn’t Mean Harmless
A systematic review of 2,631 treated plague cases found an overall mortality rate of 13.6 percent. But among patients with pneumonic plague, 31.1 percent died despite receiving antimicrobial treatment. The corresponding figures were 14.2 percent for bubonic plague and 20 percent for septicemic plague.
A separate WHO (World Health Organization) evidence review reached a similar conclusion. Among the treated cases it examined, overall mortality was 21 percent. But it rose to 29 percent for pneumonic plague and 45 percent for septicemic plague, compared with 17 percent for bubonic plague.
Those numbers require an important qualification. They include patients treated during different eras, with different antibiotics, and at different stages of disease. They do not mean that someone who develops pneumonic plague today and receives prompt, appropriate treatment has a 30 percent chance of dying. In fact, WHO emphasizes that recovery rates for pneumonic plague are high when it is detected and treated promptly, ideally within 24 hours of symptom onset.
Still, those mortality figures make one thing abundantly clear. Having an antibiotic that kills a bacterium isn’t the same thing as having unlimited time to use it. With pneumonic plague, the clock starts ticking very quickly.
Seven centuries after the Black Death, we have antibiotics that medieval villagers could scarcely have imagined. But Yersinia pestis is still perfectly capable of killing us. And scaring the hell out of us.
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