The plague never left, we just stopped looking

In the first week of October, a word that much of the world had filed under history returned to the news. A 28-year-old laboratory worker at the Irkutsk Anti-Plague Research Institute in Siberia died, and nearly 200 people were placed under observation in hospital. Plague was suspected. Russia's public health agency, Rospotrebnadzor, spoke only of pneumonia of unknown aetiology, which means an illness whose cause has not yet been identified.The reaction followed a familiar script. Alarm came first, then explanation, then the quiet relief of being told that the risk to the public is low. But the script itself deserves scrutiny, because it rests on a premise the science does not support: that plague had gone, and that its appearance is a return.It is not a return. The plague never left. We simply stopped looking.IS THE PLAGUE BACK, OR DID IT NEVER LEAVE?The bacterium behind plague, Yersinia pestis, was never eradicated. It persists in wild animals and in the fleas that feed on them, forming what scientists call natural reservoirs, meaning places where a germ survives without needing human beings at all. The World Health Organization says human plague remains endemic in several countries, with most recent cases reported in the Democratic Republic of the Congo and Madagascar. Professor Brendan Wren of the London School of Hygiene and Tropical Medicine puts the global figure at around 2,000 reported cases a year, mostly in such regions. Around 2,000 human cases are reported each year, mostly in regions where plague is endemic. (Illustration: Radifah Kabir) The disease that killed between a third and a half of Europe's people in the 14th century, by common estimates, still circulates quietly in the animal world. Scientists have even recovered its genome from the teeth of Black Death victims buried in London in 1348 and 1349, and found an ancestor of the strains that survive today.HOW DOES PLAGUE SPREAD FROM ANIMALS TO PEOPLE?Plague travels through a cycle with three parts: animal, flea and human. An infected flea bites a person, and bubonic plague begins. When infected animals die in large numbers, their fleas lose their hosts and look for new ones, and human beings can fall into that gap. Ecological disruption, animal die-offs and contact with infected animals all create opportunities for the bacterium to cross over. Then the biology can change. If the infection settles in the lungs, it becomes pneumonic plague, which the World Health Organization describes as especially contagious, because it can pass between people through respiratory particles. When infected animals die, their fleas look for new hosts, and sometimes that host is a person. (Illustration: Radifah Kabir) Madagascar showed what that can mean. In 2017, a large pneumonic plague outbreak struck the island, with many cases in its capital, Antananarivo. A disease rooted in rural ecosystems had entered a crowded city.Professor Wren adds a necessary note of proportion. Human-to-human spread of plague, he points out, is relatively uncommon compared with respiratory viruses such as the coronavirus. Plague is dangerous, and it is not easily transmitted.WHY CAN'T PLAGUE BE ERADICATED LIKE SMALLPOX?Smallpox is the only human disease the world has declared eradicated, in 1980. It was possible because smallpox lived only in people. Remove the human hosts, and the virus had nowhere left to go.Plague has other homes. It lives in rodents and other wild animals, and no vaccination campaign can reach a burrow. That is why plague is described as controlled and never as conquered, and why the difference matters. Control means we can treat the cases we find. Eradication would mean there were no cases left to find. We have achieved the first, and have been tempted to speak as though we had achieved the second.IS PLAGUE CURABLE TODAY?Yes, and this is genuine progress. Antibiotics can cure plague, provided treatment begins early. Professor Wren says pneumonic plague remains treatable with antibiotics when diagnosed promptly. Untreated, it can turn life-threatening within a day or two. Everything depends on those first hours.That is why the observation of nearly 200 people in Irkutsk, however alarming it sounds, is a sensible precaution. Professor Wren describes monitoring and isolating laboratory staff and other contacts in just those terms, and he stresses the importance of strict biosafety procedures when handling dangerous pathogens.WHAT IS ACTUALLY KNOWN ABOUT THE IRKUTSK CASE?Less than the headlines suggested. The death of the laboratory worker has been reported, and so has the observation of around 200 people. Rospotrebnadzor has described the illness as pneumonia of unknown aetiology. Some reports suggest she may have been accidentally infected after a test tube broke, a detail Professor Wren noted without confirming. Russian authorities say they have found no evidence linking her death to pathogens handled at the institute. Tests confirming plague have not been made public, and nothing so far describes an outbreak. The London School of Hygiene and Tropical Medicine assesses the risk to the public as likely low.A young woman has died, and the cause remains unresolved. That calls for care in what we say, and patience in what we conclude.WHAT SHOULD THE WORLD LEARN FROM THE PLAGUE SCARE?The most important lesson has nothing to do with Siberia. It is that modern medicine has made plague manageable, and that we have allowed manageable to slide into gone. Antibiotics improve the odds dramatically when treatment comes early. Surveillance can catch a pathogen before a local event becomes a wider one. These are real achievements, and they depend on someone continuing to look.The danger, then, is not an ancient bacterium rising from the dead. It is our habit of confusing control with eradication. Plague survives because its animal reservoirs survive, and as climate, land use, wildlife contact, urbanisation and human mobility change, the boundary between those reservoirs and us may change too. A system that has stopped paying attention is poorly placed to notice when it does.The question worth asking is not whether the Black Death is coming back. It is how many other diseases we call defeated, simply because we have grown good at containing them.- Ends