The death of a 28-year-old woman who worked in an anti-plague laboratory in Russia is raising concerns about what caused her illness.
The woman died Friday, according to the World Health Organization, with no cause of death confirmed. A Russian official said the woman died of pneumonia of “undetermined” origin and did not link her death to her work at the Irkutsk Anti-Plague Institute of Siberia and the Far East.
Darya Shipilova, 28, was identified by her mother and Russian media outlets as the lab worker.
On Tuesday, the Centers for Disease Control and Prevention said on X that it is monitoring “reports of a suspected case of pneumonic plague in the Irkutsk region of Russia that resulted in a death,” although the circumstances of the case “remain unconfirmed.”
“At this time, there is no indication of a broader threat to the United States, but CDC and our interagency partners are prepared and will continue to monitor the situation closely,” the agency posted.
Key details aren’t known, including whether the woman was infected with plague at all and, if so, whether it was naturally occurring plague or bacteria studied in the lab. Scientists also don’t know how quickly her illness progressed and what treatment she received. Nearly 200 people who came into contact with the woman are under precautionary medical observation, according to Russian media.
Officials in Russia said Tuesday that no plague had been detected in 60% of the identified group tested so far.
“Maybe it’s going to come out that she died from something unrelated and it was just a coincidence” that she worked in an anti-plague lab, said Lisa Morici, a microbiologist and immunologist in the Tulane University School of Medicine.
Dr. Ashish Jha, the White House’s former Covid response coordinator, told NBC News in an interview, “If there were weapons programs, biological weapons programs in these labs, that would be much more concerning to me.”
“We need to understand that now,” he added.
The situation is still rapidly unfolding. But here’s what we know about the pneumonic plague, how it spreads and how dangerous it is.
What is plague?
Plague is an infection caused by Yersinia pestis bacteria. Known as the “Black Death” during the 14th century, the plague triggered several global pandemics over centuries before the discovery of antibiotics.
It presents in three main forms: bubonic, pneumonic and septicemic, according to the World Health Organization. All three are caused by Yersinia pestis, but they occur in different parts of the body.
Bubonic is the most common form, Morici said. It is primarily transmitted through bites of infected fleas or direct contact with infected rodents, which can cause painful, swollen lumps in the lymph nodes. It is usually not contagious.
Left untreated, however, it can spread to the lungs and become pneumonic plague, which can pass from person to person through respiratory droplets, Morici said.
Septicemic plague occurs when the bacteria grow and spread in the blood.
How does pneumonic plague spread?
Pneumonic plague can spread through the air when an infected person or animal coughs or sneezes.
The respiratory droplets don’t travel very far, maybe three to six feet, said Dr. Dave Wagner, director of the Pathogen and Microbiome Institute at Northern Arizona University. “They drop to the ground pretty quickly.”
It’s the rarest form of the disease, according to WHO.
Dr. William Schaffer, an infectious diseases expert at Vanderbilt University Medical Center, said close contacts are most at risk. Pneumonic plague isn’t something that spreads “distantly across a room, but to face-to-face contacts,” he said.
“It’s highly unlikely for most people to get the pneumonic form of the disease,” Morici said.
Covid, for example, spreads like wildfire through the air, traveling beyond six feet.
“It’s nothing like the Covid-19 pandemic,” she said.
How deadly is it?
While pneumonic plague is the rarest form of the disease, it’s also the deadliest.
“It’s the one that’s so frightening because it can kill so quickly,” Morici said.
It progresses remarkably fast, Wagner said. Symptoms typically appear within one to two days of exposure, and patients require treatment within 48 hours of showing symptoms to prevent fatal complications. Symptoms can include shortness of breath and coughing or blood in the phlegm.
Because of how rapidly it attacks the respiratory system, public health experts consider this strain the most likely candidate for a biological attack, according to Morici.
People with pneumonic plague are often quarantined, she said. Healthcare workers will often wear personal protective equipment, such as an N95 mask, or even a full body suit in case of accidental exposure.
“We’re using the strictest levels of biocontainment,” she said.
How is it treated?
Antibiotics are highly effective against plague, including pneumonic plague.
“This is why we don’t have big plague outbreaks anymore,” Wagner said.
Are experts worried about a potential plague outbreak?
Schaffner said there’s no evidence to suggest that the plague bacteria are evolving in a way to become resistant to antibiotics. “We will not turn 2026 into the Middle Ages, where the Black Death caused vast amounts of death throughout Europe. That will not happen.”
Wagner said he has no reason to believe this suspected case of plague is “going to take off and spread.”
“The plague that we have today is the same plague that was the scourge of humanity for so long during great pandemics,” he said.
Is the plague found in the U.S.?
About seven cases of plague are reported in the U.S. each year, according to the CDC. Most occur in rural parts of the Southwest, including Arizona, California, Colorado and New Mexico. These are areas where Yersinia pestis bacteria naturally circulate among wild rodents like prairie dogs and their fleas.
Most people are treated quickly with antibiotics and recover. Deaths from the plague in the U.S. are rare but do happen.
Last July, a man in Arizona died of pneumonic plague after he was exposed to sick cats. Within a week, the man went to an emergency department with shallow breathing, a fast heart rate, chest pain and a dry cough. Despite getting antibiotics and oxygen, the man died within eight hours of his admission to the hospital. Testing later showed he had pneumonic plague.
