This disease killed 60% of Europe's population, now it's back

While you may have read about plague in history books, three recent cases in China are a stark reminder the disease is not a thing of the past.

A 55-year-old man from northern China’s Inner Mongolia Autonomous Region has been diagnosed with bubonic plague after eating wild rabbit meat. His case follows confirmation that two other people from the same region have the pneumonic form of the disease.

The two pneumonic plague patients – husband and wife – are quarantined in Beijing. Their cases are not thought to be related to the case of the 55-year-old man.

Plague is caused by Yersinia pestis, a bacteria found in small mammals and the fleas that feed on them. Humans usually get plague after being bitten by an infected flea or by handling an infected animal.

Early diagnosis and treatment with antibiotics are essential, according to the World Health Organization (WHO), which puts the fatality rate at 30-100% if left untreated.

Bubonic plague – which results in swollen lymph nodes, or buboes – is the most common type. Transmission between humans is rare at this stage, but the disease can advance and spread to the lungs (pneumonic plague).

Pneumonic plague is the deadliest and most virulent form. It’s highly contagious because it is spread when an infected person coughs. A rarer third type, septicemic plague, affects the bloodstream.

In the sixth century, between 30 and 50 million people – roughly half the world’s population at the time – died in the Plague of Justinian, which is thought to have been spread by merchant ships infested with rodents.

About 800 years later, plague wreaked havoc on Europe, killing about 50 million people, or 60% of the continent’s population.

The disease was known as the Black Death because it can cause blackening of body tissue, commonly in victims’ fingers, toes and nose.

Over the next 500 years, smaller plague epidemics continued to occur, including a major outbreak in England in 1665, in which one-fifth of London’s population died.

The third plague pandemic originated in southwestern China’s Yunnan province in the 1850s and moved along opium trade routes. By 1894, it had reached Guangzhou and Hong Kong. And from these port cities, it spread globally, resulting in more than 10 million deaths.

Though outbreaks are becoming more unusual, plague still lingers today.

Between 2010-2015, 3248 people were infected worldwide, with 584 deaths, according to the WHO.

It is most common in Madagascar, Democratic Republic of the Congo and Peru, but infections also occur in countries from China to the United States.

It’s a global problem: potential plague natural foci – the epidemiological factors needed for its transmission – are distributed around the world.

Experts have warned the risk of major pandemics that could kill tens of millions of people and cause economic and social chaos is increasing – and governments aren’t properly prepared.

According to a new report by the Global Preparedness Monitoring Board, epidemic-prone diseases such as influenza, severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), Ebola, Zika, plague, yellow fever and others are "harbingers of a new era of high-impact, potentially fast-spreading outbreaks that are more frequently detected and increasingly difficult to manage."