The Black Death is here to stay

While our world is currently consumed by the coronavirus threat who ever thinks about Bubonic Plague or the Black Death? Plague is an infectious disease that has played a critical role in our world's history. The word Plague also continues to conjure up basic fears and dreads and in many ways is related to the fear we continue to have about infectious disease and contagion.

Many people, however, continue to believe that Bubonic Plague is a thing of the past and that we have nothing to fear. But the truth is that Bubonic Plague has never disappeared and is here to stay. In addition, believe it or not, Bubonic Plague is today more geographically widespread in our world than at any time in the previous 1000 years and continues to be a threat to humans.

Historically Plague has killed hundreds of millions of people and there have been a large number of Plague pandemics over the last 700 years the last of which spread out of Asia in the late 19^th century and infected parts of Australia in the period 1900-1925.

Plague outbreaks have left an indelible imprint on our world even though we now consider them to be part of an earlier age.

The Justinian Plague in the 6^th and 8^th centuries quickly spread across Asia, North Africa, the Middle East and parts of Europe and killed millions of people. The Black Death in the 14^th century wrecked total havoc on Europe causing tens of millions of deaths wiping out one third of West Europe's population and reshaping the continent. In the 17^th century plague returned to Europe with major outbreaks in France between 1647 and 1649, London in 1665 when 10 percent of the city's population caught the disease, Holland in the 1660s and Vienna in 1679.

The last major Plague pandemic originated in the Yunnan province in south-west China in the 1880s and spread to Hong Kong from where it was carried by ships around the world. By 1900 had spread to many parts of the world infecting North and South Africa, the USA, Honolulu, South America and Portugal as well as Australia. In Australia 1400 people caught plague between 1900 and 1925 and 535 died from the disease.

After this pandemic ran its course people believed that Plague had had its day and that the advent of a Plague vaccine and antibiotic drugs spelt the end of our worries. Plague was then largely forgotten and placed on the lowest rungs of infectious disease risk.

But the truth is that Plague has never disappeared and remains a critical issue for our world today. From the 1980s our world has seen a steep upward trend in the number of plague cases particularly in Africa.

The Democratic Republic of the Congo and Madagascar have experienced Plague outbreaks in virtually every year over the last three decades. Between 1954 and 2019 the world has seen more than 100,000 cases of Plague and more than 9,000 deaths. Today there are a few thousand cases of Plague reported every year with a death rate between 5 and 15 percent and important epidemics continue in parts of Africa and Asia.

Plague is a zoonotic bacterial infection well adapted to surviving in permanent natural reservoirs with its animal hosts. Over 200 species of ground-living rodents have been found to support the disease. In such an environment the Plague bacillus has adapted perfectly to its host's life style, hibernating when the animal hibernates only to revive with the animal in Spring. Some of its host animals do not catch the infection, others do in a minor way and rarely an epizootic occurs and it is during this time that humans and other species become vulnerable to infection.

In 1894 during the last pandemic Yersin identified the bacterial agent responsible for the disease (Yersinia Pestis) and a few years later Ashburton-Thompson in Australia revealed that the disease was spread by fleas. Today, Plague is a classic zoonosis permanently maintained in animal reservoirs throughout many parts of Asia, Africa, Latin America and the USA.

Allied to this, Plague remains closely linked to poverty in many parts of the developing world where poor drainage, slum and shanty housing, lack of water and sheer poverty enables the survival of large rat colonies.

But Plague is much more than this.

In the Western USA, for example, plague has been present for more than 100 years and has established permanent reservoirs among ground living rodents which have proved impossible to remove. Every year a few cases of human Plague are reported in Arizona, Colorado, Oregon, Nevada, New Mexico and California and have been shown to spread from a wide variety of animals including rats, deer mice, rabbits, prairie dogs and foxes.

But apart from Bubonic Plague spread by animals and fleas there is another form of plague that is even more deadly – Pneumonic Plague. Pneumonic Plague is the most severe form of plague spread by the inhalation of infected droplets from an infected person. The Pneumonic Plague epidemic that broke out in Manchuria in 1910-1911 remains the most severe outbreak our world has experienced although cases of pneumonic plague still present themselves. In Manchuria possibly 60,000 people died from Pneumonic Plague in 1910-11. Pneumonic Plague remains the deadliest of all Plagues and without immediate treatment is invariably fatal.

In Australia are we under any threat from the Plague today?

Well given an increasingly mobile world where tens of millions of people cross international borders by air every month there is always the threat of an infected person carrying the disease back to Australia. More significantly however, perhaps Plague never disappeared from Australia after the 1900-25 pandemic but simply retreated back into a natural reservoir of an Australian animal host.

But what evidence exists that Plague infiltrated Australian wildlife in 1900-25?

Well, in 1902 during the human pandemic in Sydney a large number of native animals in the Zoological Gardens died from Plague and over the next five years Plague wrecked havoc among native rodents along the Clarence River as well as among native rats in the Mossman District near Port Douglas. This is exactly what happened in the USA between 1900 and 1920 after which Plague permanently established itself among a variety of ground-living animals. Could this have also happened in Australia? We do not really know and to the best of the author's knowledge rural native animals in Eastern Australia have never been tested for Plague.

There is little doubt that a large Plague outbreak in our world or in Australia would place extraordinary pressure on health-care resources and create scenes of considerable fear and panic. But are we really safe?