A person in the US has died from pneumonic plague. It’s not just a disease of history

A person in Arizona has died from the plague, local health officials reported on Friday.

This marks the first such death in this region in 18 years. But it’s a stark reminder that this historic disease, though rare nowadays, is not just a disease of the past.

So what actually is “plague”? And is it any cause for concern in Australia?

There are 3 types of ‘plague’

The word “plague” is often used to refer to any major disease epidemic or pandemic, or even to other undesirable events, such as a mouse plague. Naturally, the word can evoke fear.

But scientifically speaking, plague is a disease caused by the bacterium Yersinia pestis.

Plague has three main forms: bubonic, septicemic and pneumonic.

Bubonic is the most common and is named after “buboes”, which are the painful, swollen lymph nodes the infection causes. Other symptoms include fever, headache, chills and weakness.

Bubonic plague is typically spread by fleas living on animals such as rats, prairie dogs and marmots. If an infected flea moves from their animal host to bite a human, this can cause an infection.

People can also become infected through handling an animal infected with the disease.

Septicemic plague occurs if bubonic plague is left untreated, or it can occur directly if the disease enters the bloodstream. Septicemic plague causes bleeding into the organs. The name comes from septicemia, which refers to a serious blood infection.

The recent death in the United States was due to a case of pneumonic plague, which is the most severe form. Bubonic plague can in some cases spread to the lungs, where it becomes pneumonic plague. However, pneumonic plague can also spread from person to person via tiny respiratory droplets, in a similar way to COVID. Symptoms are similar to the other forms but also include severe pneumonia.

Some 30–60% of people who contract bubonic plague will die, while the fatality rate can be up to 100% for pneumonic plague if left untreated.

Plague: a potted history

This disease is one of the most important in history. The Plague of Justinian (541–750CE) killed tens of millions of people in the western Mediterranean, heavily impacting the expansion of the Byzantine Empire.

The medieval Black Death (1346–53) was also seismic, killing tens of millions of people and up to half of Europe’s population.

Spread by the growing trade networks of the British empire, the third and most recent plague pandemic spanned the years 1855 until roughly 1960, peaking in the early 1900s. It was responsible for 12 million deaths, primarily in India, and even reached Australia.

It’s believed the bubonic plague was largely behind these pandemics.

Plague in the modern day

First introduced into the US during the third pandemic, plague infects an average of seven people a year in the west of the country, due to being endemic in groundhog and prairie dog populations there. The last major outbreak was 100 years ago.

Deaths are very rare, with 14 deaths in the past 25 years in the US.

Globally, there have been a few thousand cases of plague over the past decade.

The countries with the most cases currently include the Democratic Republic of the Congo, Madagascar and Peru, with cases also occurring in India, central Asia and the US. Cases usually occur in rural and agricultural areas.

Plague can be treated

Plague can easily be treated with common antibiotics, typically a course of 10–14 days, which can include both oral and intravenous antibiotics. But it must be treated quickly.

The recent death is concerning, as it involves the airborne pneumonic form of the disease, the only form that spreads easily from person to person. But there’s no evidence of further spread of the disease within the US at this stage.

As Y. pestis is not found in Australian animals, there is little risk here. Plague has not been reported in Australia in more than a century.

But plague, like many diseases, is influenced by environmental conditions. The risk of climate change causing an expansion in the habitat of animal hosts means public health experts around the world should continue to monitor it closely.

The plague, though often perceived as a disease of history, is still with us and can pose a major health threat if not treated early.