What is the pneumonic plague?

The bacteria that causes bubonic plague. Science Source hide caption

NPR's Russia correspondent Charles Maynes reported this week on what we know about a Russian researcher working in a lab studying the plague who died from pneumonia of an unknown origin last week.

Maynes reports that the employee was a 28-year-old woman who worked in a lab in Siberia, some 2,500 miles from Moscow. An investigation by Russia's consumer health watchdog concluded that no pathogens in her body were connected to her work with infectious disease.

But local media have raised concerns about the spread of pneumonic plague, which NPR has not independently confirmed.

It's one of the diseases studied at the lab in Siberia. It's airborne and can be fatal.

While noting that 200 "contacts" were in quarantine, Russia has denied that there are cases of plague in the area. But questions loom. In a press conference Wednesday, the head of the World Health Organization, Tedros Adhanom Ghebreyesus said these Russian assurances were — at the very least — incomplete: "We don't yet have the full picture of this event and we're not able to conduct a full risk assessment. "

In the meantime, here's what we do know about the bacterial disease of plague — and the variant known as pneumonic plague.

The plague comes in several versions, depending on which body part the bacteria invade. When a flea bites a person, the individual typically develops what's called bubonic plague. In this case, the telltale sign is one or more swollen and painful lymph nodes, known as buboes. (The word "bubonic" comes from the Greek boubon , which means groin, because some people have swollen lymph nodes in their groin.) Doctors can diagnose the disease by taking a sample from the person's blood or lymph nodes and then submitting the sample to a lab for testing.