The bubonic plague is back. Should you be worried?

First, what is the bubonic plague?

The plague is caused by Yersinia pestis, a zoonotic bacteria, i.e. bacteria that can spread between animals and people. Y pestis is usually found in small animals and their fleas.

Yersinia pestis in the foregut of the flea vector, under an electron microscope. (National Institute of Health, US)

According to the World Health Organisation (WHO), humans can be infected in one of three ways — “the bite of infected vector fleas”, “unprotected contact with infectious bodily fluids or contaminated materials” (like bitten by an infected rat), and “the inhalation of respiratory droplets/small particles from a patient with pneumonic plague”.

What are the disease’s symptoms?

Plague symptoms can manifest in a number of ways. Bubonic plague specifically refers to cases where bacteria gets into the lymph nodes. According to the United States’ Centre for Disease Control and Prevention (CDC), it can cause fever, headache, weakness and painful, swollen lymph nodes, and usually happens from the bite of an infected flea

Septicemic plague happens if the bacteria enters the bloodstream. This often follows untreated bubonic plague, and causes additional, more serious symptoms. These include abdominal pain, shock, bleeding into the skin, and blackening of appendages, most often fingers, toes or the nose. According to the CDC, this form comes either from flea bites or from handling an infected animal.

Pneumonic plague is the most dangerous, and according to the WHO, “almost always fatal” if untreated. As the name suggests, it happens when the bacteria enters the lungs, and adds rapidly developing pneumonia to the list of symptoms. According to the CDC, it is the only form of plague that can be spread from person to person by inhaling infectious droplets — also making it the most contagious.

What was the impact of the Black Death?

The Black Death was the single most deadly disease outbreak in history till the Great Influenza pandemic of 1918-20. Taking into account the significantly lower population levels of the 14th century, the Black Death is still the most deadly outbreak of all time, by some estimates, wiping out up to half of Europe’s population.

More than anything, it left a lasting impact on those who survived. A study published in 2022 in the journal Nature found that certain genetic mutations increased survival chances by around 40 per cent. This 40 per cent “was the strongest selective fitness effect ever estimated in humans,” Professor Luis Barreiro, of the University of Chicago, told the BBC.

Unfortunately, this mutation, which has since been passed, has been directly linked to the incidence of certain autoimmune diseases — meaning what happened 700 years ago might be impacting your health today.

The Black Death also left lasting social, economic and cultural impacts in Europe and beyond. Historian James Belich, in his 2022 book The World the Plague Made: The Black Death and the Rise of Europe argues that European global dominance can be directly traced to the mediaeval pandemic. Although this might be an oversimplification, it nonetheless provides an interesting insight into the story of the “Great Divergence” which continues to shape the world today.

So, should you be worried about another Black Death?

No. Doctors do not expect the disease to spread from Oregon or cause any deaths among humans.

Bubonic plague epidemics became a thing of the past by the 1930s. Today, according to the CDC, a couple of thousand plague cases are reported worldwide each year, mostly in Madagascar, the Democratic Republic of Congo, and Peru. Fatality is roughly 11 per cent.

This is because of modern antibiotics, which are fairly capable of dealing with the danger posed by Y pestis, as well as better hygiene and understanding of the disease. According to the CDC, all forms of plague are treatable with common antibiotics, with early treatment drastically improving chances of survival.

Even though Y pestis can still occur almost anywhere, and can be fatal to individuals, a larger pandemic echoing the Black Death is thus pretty much impossible.