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Let's Just Calm Down About the Bubonic Plague—For Now

You have worse infections to be scared of.
November 1, 2015, 3:00pm
Masks worn during experiments with Plague. Philippines, probably around 1912. Image: Otis Historical

By now you're probably aware of the one-person bubonic plague outbreak that hath descended up a small Oregon county. This was confirmed by officials on Friday, who identified the victim as a teenager unfortunate enough to get bitten by a plague-bearing flea while on a hunting trip. She's been hospitalized since Oct. 24, though much detail hasn't been revealed about her condition—just that she's recovering.

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The words "bubonic plague" conjure up Dark Ages images of firewood-stacked corpses and rapid population decimation—you know, "bring out your dead"—but, in the modern era, it's pretty low on the list of rational fears, even you were to catch it. Most antibiotics are effective in treating the infection, cutting the bubonic plague mortality rate down to between 1 and 15 percent. In untreated cases, however, that rate shoots up to 40 to 60 percent.

Moreover, bubonic plague isn't particularly transmissible. It persists mainly among rodents and is passed back and forth between them and their flea entourages. These rodent-flea cycles have been going on for some 6,000 years.

Bubonic plague goes a little something like this:

If the vector is a flea, bacillus proliferates in the flea's esophagus, preventing food entry into the stomach. To overcome starvation, the flea begins a blood-sucking rampage. Between its attempts to swallow, the distended bacillus-packed esophagus recoils, depositing the bacillus into the victim's skin.

The bacillus invades nearby lymphoid tissue, producing the famous bubo, an inflamed, necrotic, and hemorrhagic lymph node. Spread occurs along the lymphatic channels toward the thoracic duct, with eventual seeding of the vasculature. Bacteremia and septicemia ensue. The bacillus potentially seeds every organ, including the lungs, liver, spleen, kidneys, and rarely even the meninges.

Human to human transmission is next to impossible, requiring direct contact with infected tissue. Flea bites are far and away the most common vector, but scratches or bites from infected rodents can pass it on as well. It's carried by more than 200 different species of rodent and is present in all parts of the world.

Bubonic plague has two less-forgiving siblings: pneumonic plague and septicemic plague. Together, these two varieties make up around 5 percent of all plague infections. They're also far and away the most deadly: septicemic plague has a 40 percent mortality rate in treated cases and 100 percent mortality rate in untreated cases, while pneumonic plague is pretty much a death sentence, with a 100 percent mortality rate if not treated within the first 24 hours of infection.

Fortunately, these two versions are pretty rare. Pneumonic plague requires contact with an aerosolized form of the bacteria, which is unlikely to occur naturally, but may be engineered as in the case of biological weapons. Meanwhile, septicemic plague requires a bite (flea, most likely) to occur inside of the victim's mouth or throat, allowing it to jump directly into the bloodstream. It can happen.

The future of plague

Again, plague is incredibly common worldwide. It's just not common among humans. Modern sanitation means we don't have herds of rats and mice—and their parasitic flea followers—cruising around our living spaces. Also, at least in the United States, plague exists primarily in rural animal populations. This is where most humans catch it.

It's feared that plague with undergo a significant resurgent in coming years, for a variety of reasons. One of these is climate change. A 2006 study found that, "by using field data from 1949–1995 and previously undescribed statistical techniques, we show that Y. pestis [plague] prevalence in gerbils increases with warmer springs and wetter summers: A 1°C increase in spring is predicted to lead to a [greater than] 50 percent increase in prevalence." It alsonotes that plague-favoring climactic conditions existed at the outset of the Black Death as well as more recent pandemics in the same regions (Europe, Western Asia).

Making the situation worse is the ongoing population explosion, which has the effect of pushing human settlements further and further into rural areas and, thus, increasing their contact with wildlife. Helping things along, we can expect increasing overpopulation and decreasing sanitation to come alongside increasing urbanization.

To some degree, it seems, plague is just lying in wait.