Explainer-What do we know about plague institute lab worker's death in Russia?

MOSCOW/LONDON, Oct 6 - A laboratory worker at a plague research institute in Siberia fell ill and died in undisclosed circumstances on October 2, prompting authorities to 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.

Russian media named the victim as Darya Shipilova, a 28-year-old laboratory worker at the Irkutsk Anti-Plague Research Institute of Siberia and the Far East.

The authorities said she died of an unknown type of pneumonia but that as a precaution they quarantined everyone who had come into contact with her.

Unconfirmed reports of how she fell ill have circulated on social media.

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. 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.

There is no confirmation she died from plague although one regional governor said she "may" have died from plague.

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.

Elena Sofina, a local official in Siberia, said 60% of those quarantined had since been released. Local media said about 200 were initially quarantined.

Sofina said "a dangerous diagnosis" had not been confirmed.

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 over 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.

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 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.

US President Donald Trump said the laboratory worker's death was a "big problem for Russia" and offered to help Moscow deal with it. US Secretary of State Marco Rubio said Russia should share more information about the death.

The WHO in Geneva said Russia had told it there were no plague cases in the city of Irkutsk. Reuters could not establish whether this meant plague could be ruled out in the lab worker's case.

Kazakhstan, Kyrgyzstan and Uzbekistan said they were stepping up precautionary measures at their borders to guard against the possible spread of infectious diseases.

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.

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 persons 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. REUTERS