Thomas Jeffries, Senior Lecturer in Microbiology, Western Sydney University

Conflicting information about the death of a lab worker at a Russian plague research institute has fueled fears about the possibility of pneumonic plague spreading.

Nearly 200 people are in quarantine in Siberia after 28-year-old Darya Shipilova fell ill at work and later died on October 2.

The exact circumstances of her death are unknown. A senior Russian official posted on social media last week that Shipilova “had died from the plague” – before editing the post to add “possibly”. Russia’s health watchdog has since stated she died from “pneumonia of unknown etiology”.

Local media reports suggested she was infected following an accident at the lab where she worked, the Irkutsk Anti-Plague Research Institute of Siberia and the Far East. But these have not been confirmed.

So, what is plague, and how does it spread? Should we be worried?

Plague is caused by the bacterium Yersinia pestis. The bacteria generally live in ground-dwelling rodents such as rats and prairie dogs, but can also infect humans.

The same Y. pestis bacteria can cause three different types of plague.

Bubonic plague is spread from animals to humans by fleas, and causes swelling (called buboes) in the lymph nodes. Other symptoms include fever, headache, chills and weakness.

Bubonic plague can kill within a few days if antibiotics are not used. Between 30–60% of people who contract this form of plague will die.

Septicemic plague occurs if bubonic plague is left untreated, or it can occur directly if the disease enters the bloodstream. Septicemic plague causes bleeding into the organs; the name refers to the serious blood infection, septicemia, that this form of the disease can cause.

Pneumonic plague – the suspected but unconfirmed cause of Shipilova’s death in Siberia – can occur when bubonic plague spreads to the lungs. But pneumonic plague can also spread from person to person via tiny respiratory droplets.

Pneumonic plague is the rarest but most severe form. The fatality rate is up to 100% if left untreated.

In addition to the other symptoms, pneumonic plague also includes severe pneumonia – an infection of the lungs, in this case caused by bacteria.

Bubonic plague was responsible for the death of tens of millions of people in the western Mediterranean between 541–750CE (the Plague of Justinian) and killed up to half of Europe’s population in the middle ages (the Black Death).

But there have been outbreaks since medieval times.

A third pandemic spanning the end of the nineteenth century and beginning of the twentieth killed up to 12 million people.

Plague is still endemic to Central Asia, Africa, the Americas and Siberia, where the Russian lab worker died last week. This means it is present at a steady, consistent level in these regions.

Cases typically occur in rural and agricultural areas which makes a potential lab leak in an urban area unusual.

Yes. A 10–14-day course of antibiotics (either oral or intravenous) treats the plague – as long as they are taken soon after infection.

However, since 1995, several antibiotic-resistant strains have been detected in the wild.

In the 1980s, Soviet Union scientists also engineered resistant strains – this history forms the basis of hypothetical scenarios involving biological warfare.

However, there is no evidence the strain alleged to have killed Shipilova could not be treated by antibiotics or that the lab is researching biological weapons.

There has only been one documented major outbreak of the pneumonic plague, in the 1910s in China.

We still don’t know much about the case in Siberia. But at this stage, there’s little evidence to cause concern about potential for an epidemic (which is localized) or a pandemic (which involves multiple countries).

In a statement on Monday, the World Health Organization (WHO) said it was aware of reports a laboratory worker in Irkutsk had “died of severe pneumonia” but no cause of death had been officially confirmed.

The WHO statement also said: “Based on unofficial information available, the public health risk to the general population appears to be low. The risk assessment will be updated once more information is available.”

To assess this risk, access to transparent information about how Shipilova fell ill and died will be essential.

This article is republished from The Conversation under a Creative Commons license. Read the original article.

(TheConversation/APC)