The mother of a young Russian scientist who died following a suspected plague leak has denied reports her daughter was infected after breaking a test tube containing deadly bacteria.

Lab technician Darya Shipilova, 28, died on October 2 after she fell ill while working at the Siberian anti-plague research institute in Irkutsk. 

Though her death was initially attributed to the 'plague' by local officials, these statements have since been retracted. 

The Kremlin has dismissed the claims, instead saying she died from 'pneumonia of unknown aetiology [origin]' 

Local media claimed Darya, whose home has since been disinfected by PPE-clad workers multiple times, may have been infected after she broke a test tube containing bacteria. 

But her mother, medical professional Svetlana Shipilova, denied this account of her daughter's death, saying it is 'impossible' to break the test tubes used in these research institutions. 

She said: 'I don't want to read nasty things about my child. I know the truth. I find myself fending off foolish acquaintances who actually believed all that.

'The smart ones, of course, didn't believe it. Not even all medical professionals realise that it's impossible to break the test tube – even if you hurl it against a wall.

'Only an amateur would say something like that. Even hypothetically, it's simply impossible to spill or break it. They are so heavily protected.'

Svetlana added because she and other relatives have been locked up in quarantine, she has not been able to bury her daughter, saying: 'Who is going to bury her if we are sitting here imprisoned?' 

She said of her daughter: 'She was such a hard worker. A pure, truly pure soul. It was hard for her superviser, because she knew Dasha and knew exactly why she was hiring her.

'It is very difficult to get a job at the [Irkutsk] Anti-Plague Institute.

'She had watched Dasha work during her internship and realised she was a genuinely decent person – a real workaholic.'

At 10pm on the night Darya died, three vehicles pulled up outside Shipilova's two-storey apartment block in Irkutsk, local media reported.  

Workers wearing orange protective suits and gas masks carried containers before treating both entrances to the building with a pungent chemical.

The smell was so acrid that neighbours had to open the doors because they could barely breathe, said a resident.

The workers were sent by Russian health watchdog Rospotrebnadzor.

They told locals: 'Some girl died, a deadly dangerous virus.' Since then, the building has been twice more disinfected.

Yesterday reports of a second unconfirmed case of plague in Siberia struck, causing the World Health Organisation (WHO) to demand answers from Russia. 

But Kremlin continued to stonewall the international body, claiming: 'No case of this dangerous disease has been recorded in the city of Irkutsk.'

The plague, the rare bacterial infection infamously known for killing tens of millions in 14th-century Europe, never went away but is now easily treated with antibiotics.

Since the Nineties, most human cases have been reported in Africa, especially Congo and Madagascar, according to WHO.

There are an average of about seven human cases per year in the US, according to the Centres for Disease Control and Prevention, mostly in rural areas of the American West.

'People think the plague is gone, it was something that occurred 500 years ago. It's not. It's here amongst us,' said Simon Clarke of the University of Reading. 

'Unless you get rid of those wild animals, which of course is not possible, then you're not going to get rid of the bacteria.' 

People in Siberia have been dying of plague for at least 5,500 years. The earliest evidence of a form of the disease was found in teeth from ancient hunter-gatherers north of the region's Lake Baikal.

Pneumonic plague and the more well-known bubonic plague – also called the Black Death – are caused by the same bacteria, called Yersinia pestis.

The bacteria spread naturally among rodents like prairie dogs and rats. Fleas that jump from infected animals and bite people can spread the disease.

The bubonic plague is the most common form of the infection. It causes painfully swollen lymph nodes that are most commonly found in the groin, armpit and neck, called buboes. Other symptoms include sudden high fever and chills, headaches, and pain in the abdomen, legs and arms, according to the Cleveland Clinic.

There are two other forms of the plague: pneumonic plague, which can be caused by inhaling the bacteria, infects the lungs, while septicemic plague is an infection in the bloodstream. Both are fatal if not treated early, according to WHO.

Bubonic plague will often develop into the other two forms of plague if untreated. 

Other than bites from infected fleas, people can also get plague by touching infected bodily fluids, so health experts recommend taking extra care when handling dead or sick animals.

The plague can also spread through the respiratory droplets of someone who has pneumonic plague.

'If you cough, you can spread it to another person, but that doesn't travel very far,' said Dr Glenn Wortmann, MedStar Washington Hospital Centre. 'So you really need to be in face-to-face contact with that person to get pneumonic plague.'

That's why 'the chance of this spreading widely in Russia and then extending here to the US will not happen,' he said.