By Andrew Osborn and Jennifer Rigby
MOSCOW/LONDON, Oct 8 (Reuters) - A laboratory worker at a plague research institute in Siberia fell ill and died in undisclosed circumstances on October 2, prompting authorities to initially quarantine about 200 people and causing public health fears on social media.
Here's what we know about the case, which officials have not linked to her work or plague, and about the disease she studied.
WHAT HAPPENED?
The as yet not fully explained death of Darya Shipilova, a 28-year-old
laboratory worker at the Irkutsk Anti-Plague Research Institute of Siberia and the Far East, prompted authorities in Russia to swiftly roll out a series of precautionary anti-epidemic measures that caught global attention.
The authorities said she had died of an unknown type of pneumonia but that, as a precaution, they had quarantined everyone who had come into contact with her.
They have since said that 90% of those people quarantined have been released after nearly 5,000 lab tests, that no plague cases have been detected in anyone she came into contact with, and that Shipilova herself was vaccinated and therefore "immune to the dangerous infections with which she worked".
Russia's health regulator said on Wednesday there were no risks of an epidemic breaking out and that it was winding down its precautionary measures.
Unconfirmed reports of how Shipilova fell ill quickly circulated on social media after her death, however.
One version said she had dropped a test tube containing live bacteria at work, a theory rejected by Russia's health watchdog. Another said she became sick after travelling to Thailand or Moldova. A third said she fell ill after going to an area near the border with Mongolia.
There is no evidence in the public domain to support any of those theories.
DID SHE DIE OF PLAGUE?
There is no confirmation she died from plague although one regional governor initially said she "may" have done so.
Health watchdog Rospotrebnadzor said she died of an unknown type of pneumonia and that no relevant pathogens had been found in anyone who came into contact with her.
It has not yet said, however, what caused the pneumonia that killed her or how she fell ill. Pneumonia, a lung infection, can have a variety of causes, including plague, as well as other bacterial infections or viral respiratory diseases, such as flu or COVID-19.
WHAT IS PLAGUE AND CAN YOU TREAT IT?
Plague circulates mainly among small animals and fleas. Caused by the bacterium Yersinia pestis, it can also infect humans. Outbreaks include the "Black Death", which killed more than 50 million people in Europe in the 1300s.
It is transmitted between animals and humans by the bite of infected fleas, inhalation of infected respiratory particles and — rarely — ingestion of infectious materials. The disease's mortality rate is 30%-100% if left untreated. If identified quickly, plague can be treated with antibiotics.
HOW COMMON IS PLAGUE?
Plague is endemic in many African countries, the former Soviet Union, the Americas and Asia, but most human cases in the last six years were reported from the Democratic Republic of the Congo and Madagascar, according to the World Health Organization.
Plague is endemic to Siberia, location of the first known prehistoric human outbreak, as Yersinia pestis is present there among small wild mammals and their fleas. It's rare for Russians to have plague.
WHAT ABOUT INTERNATIONAL REACTION?
The World Health Organisation in Geneva has asked Russia to share more information about the case, as has the United States, though President Donald Trump said on Wednesday he believed that Moscow had the situation under control and that the US did not think Shipilova's death had been caused by a bioweapon, a theory which has been the subject of speculation on social media.
Kazakhstan, Kyrgyzstan and Uzbekistan have said they were stepping up precautionary measures at their borders to guard against the possible spread of infectious diseases.
Russia is a full member of the WHO, which has a representative office in Moscow.
WHAT IS THE PLAGUE INSTITUTE IN SIBERIA?
The Irkutsk Anti-Plague Research Institute of Siberia and the Far East was set up in 1934 to control plague outbreaks. Its founding scientist helped quell outbreaks in Siberia, Mongolia and China, its website says. It later worked with other dangerous diseases, including cholera and anthrax.
WHAT ARE THE TYPES OF PLAGUE?
Plague comes in three forms affecting different parts of the body. Pneumonic plague, the most virulent and least common form, is an infection of the lungs which prompts patients to cough out infectious airborne droplets.
Bubonic plague is the most common form, occurring chiefly when an infected flea bites a person, and causes swollen lymph nodes or "buboes". Septicemic plague, which does not spread from person to person, occurs when plague bacteria multiply in the blood.
One form of plague can develop into another.
Infected people usually start with flu-like symptoms after an incubation period of one to seven days. They experience fever, chills, head and body aches and weakness, vomiting and nausea.
WHY IS THIS DEATH IN THE SPOTLIGHT?
The COVID-19 pandemic heightened concerns about the risk of new deadly diseases emerging, and reports of clusters of unknown illness or laboratory accidents now cause panic online.
Most scientists believe the coronavirus that caused COVID-19 came from animals, but some have suggested a lab leak caused it.
Public health experts have urged caution about the incident in Siberia, saying only one case has been reported and that Russian authorities say there is no evidence the lab worker was infected with plague.
(Reporting by Andrew Osborn and Jennifer Rigby; Writing by Adam Jourdan; Editing by Timothy Heritage and Alex Richardson)
