A suspected case of plague in Siberia has triggered international concern, with the US saying it is monitoring the situation “closely” and the World Health Organization requesting more information.
Russian officials have imposed sweeping quarantine measures in Irkutsk, where a lab worker at a local plague research centre died in hospital of pneumonia of “unknown” origin, according to the authorities. Officials said that micro-organisms associated with her professional activities were not detected and insist there has been no outbreak.
On Wednesday, the WHO said it had requested further information from Russia to clarify “the cause of the severe pneumonia, the pathogen that prompted the public health measures, and media reports of a second employee with pneumonia of an undetermined cause”.
Russia’s health watchdog said on Wednesday that it had sent information regarding the situation in Irkutsk to WHO.
This is what we know about the disease and the potential threats it presents.
What is the plague?
Plague is a so-called zoonotic disease that spreads from animals to humans and is often fatal if untreated. It is transmitted to people via fleas that live on small mammals such as rats. It can spread from person to person via respiratory particles or contact with contaminated body fluids or materials.
The most common type is bubonic plague. The pathogen multiplies in the lymphatic system and, if left untreated, can cause the open pus-filled sores for which the disease is infamous. If the bacteria spread to the lungs or blood, bubonic can evolve into two other forms — pneumonic and septicaemic — that are usually fatal.
It is possible to contract both pneumonic and septicaemic plague directly. Pneumonic plague is the most contagious form from person to person. It can trigger severe epidemics, according to the WHO, although it is less transmissible than some viruses such as Covid-19.
What outbreaks have we seen in the past?
Plague has historically caused devastating pandemics that loom large in popular culture and folk memory many centuries later.
It is believed to have caused the so-called “Black Death”, estimated to have killed tens of millions of people in Europe in the 1300s. Since this happened long before the development of the germ theory of how invading microbes cause disease, people lacked the knowledge as well as the medical means to curb the spread.
What do we know about this case, and what have Russian authorities said?
The lab worker, Daria Shipilova, died in a hospital in Shelekhov near Irkutsk on October 2. She had been admitted three days earlier.
Several local and federal news outlets reported, citing unnamed sources, that Shipilova died from pneumonic plague. The reports referenced various accounts of how she may have contracted it, but there has been no official or authorised confirmation.
Russia’s chief sanitary doctor visited Irkutsk the same day because of what the local governor described as “a suspected case of a particularly dangerous infection”.
The governor said that all of Shipilova’s contacts had been placed under observation. Local officials said Shelekhov hospital had been de facto quarantined.
Russia’s health watchdog Rospotrebnadzor said two days later on October 4 that Shipilova died from a “pneumonia of unknown” origin. The regulator added that her biological samples “did not detect any micro-organisms linked to her professional work”.
Shipilova’s mother, also a medical worker, told a local media outlet on October 5 that she had yet to receive the official conclusion on her daughter’s death.
The anti-plague facility where Shipilova worked is one of a few such research institutes in Russia and in the world. Her scientific publication history shows that she studied the antibiotic resistance of Yersinia pestis — the bacterium that causes plague — in natural reservoirs.
How common is the plague in the world today?
Plague bacteria still circulate in animals, meaning that there is a permanent so-called “reservoir” of the pathogens. These jump across to humans from time to time.
It is found on all continents except Oceania, according to the WHO. Since the 1990s most human cases have been reported in Africa, particularly in Madagascar and the Democratic Republic of Congo. Cases have also been reported in recent years in Mongolia, which shares a long border with Russia, but large plague outbreaks are now extremely rare in Russia and its neighbours.
Estimates of the number of human plague cases worldwide annually run to 1,000 or more. An average of seven human plague cases is reported each year in the US, according to the country’s Centers for Disease Control and Prevention.
“Plague itself has not disappeared,” said Piero Olliaro, a professor at the University of Oxford’s Pandemic Sciences Institute. “Around 200 rodent species can harbour the bacterium, with reservoirs found across the Americas, Eurasia and Africa. Sporadic human cases therefore continue to occur.”
Once identified, plague transmission chains can be broken by isolating infected patients. They can be treated successfully with antibiotics if the disease is identified early on.
What other questions are raised by the Russian case?
The case has raised questions about whether the bacteria came from a biological research facility.
There are legitimate reasons to keep pathogens in secure facilities, notably to better understand diseases and improve potential treatments for them. Accidental lab leaks of microbes do sometimes happen — and when they do it is important to understand why, to help prevent a repeat.
Such research facilities have capabilities to work on potential bioweapons, by engineering pathogens to make them more transmissible or more deadly — or both.
On the face of it, plague bacteria would not be the most obvious choice for this, since they do not spread between people as easily as some other known pathogens and are treatable with existing drugs.
Alongside plague, the Irkutsk institute studies other pathogens that would be better suited for use as biological weapons because of their lethality, including anthrax.