LEADING scientists are frantically working to develop a vaccine for the PLAGUE amid fears terrorists could kill millions if they weaponized the deadly bacteria.

The Medieval disease famously wiped out one third of Europe's population in the 13th and 14th centuries in one of the most devastating pandemics in human history now known as the Black Death.

4 The plague wiped out one third of Europe's population in the Medieval pandemic known as the Black Death (illustrated) Credit: Alamy

4 Millions in Britain were also killed by the disease during the Middle Ages Credit: Alamy

Today the disease - which has a 90 to 100 per cent mortality rate - has been classed by the World Health Organisation as a "re-emerging human pathogen".

Dr Ashok Chopra, a professor of microbiology and immunology at the University of Texas, is leading studies he hopes will develop a vaccine to counter all three strains.

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He told The Sun Online: "We are specifically looking at pneumonic plague because the mortality rate associated with pneumonic plague is very high - almost 100 percent."

Bubonic plague is the most commonly recognised strain of the disease - but the pnuemonic variant is much more virulent, and unlike bubonic, is spread via airborne particles.

"If terrorists use those organisms - they could utilise the bacteria. It could lead to mass deaths in a very short period of time. It would spread very, very quickly.

"Think about the bubonic plague in Europe in the 13th, 14th century. One third of the population was wiped out because of infection. That's the typical scenario that you should think of.

"At the time it started with the bubonic plague and then it went to the pnuemonic plague and one third of the population died so the consequences could be enormous."

His team's lab research had so far shown promising results on rats - they were successfully vaccinated for five months against the disease.

4 Pictured is microscopic plague bacteria, known by its scientific name Yersinia pestis Credit: Dr Ashok Chopra

The Department of Defence has also taken interest in his work and he hopes to receive additional government funding to begin testing on primates.

He said: "It's very easy to grow, the bacteria, you don't need any sophisticated equipment so if it falls into the wrong hands they can grow it and spread it easily.

Such a scenario is not unheard of. In the Second World War, Imperial Japan dropped thousands of plague-infested fleas on Chinese cities.

Developed at its covert "Unit 731" biological and chemical warfare facility, these attacks are believed to have killed around 400,000 civilians.

Dr Chopra added: "We had more cases of plague in 2015, 2016, after a very long period of time. The last case was in 1924 in LA... then it was 2015, 2016.

"So that is quite scary, that there may be more cases of natural infections in the area - so it is important not only for cases of terrorism."

4 Research is underway at the University of texas Medical Branch (pictured) to develop the vaccine Credit: Google Streetview

Currently there are antibiotics available to counter the disease, but Dr Chopra warned they are ineffective if not administered within a day of the onset of symptoms. With most doctors having little experience of the disease, it is unlikely it would be identified before it's too late.

And given the symptoms are easily mistaken for that of a common flu, he said it was imperative a vaccine is developed.

"The window for antibiotic treatment is very narrow, so it is usually between 20 - 24 hours after the appearance of the symptoms of the disease. If you delay the treatment then you will still see people dying.

"Therefore it's very important that we have a vaccine to be given to people, especially to military people who go overseas."

A HISTORY OF PLAGUE AS A BIOLOGICAL WEAPON Given the virality of the plague, history is littered with instances of it being used as a biological weapon. Historical accounts from the far east describe it being used by the Mongols, Huns and rampaging Chinese armies to infect adversaries. This involved catapaulting infected animals or corpses of plague victims into besieged cities, or dumping them into water supplies to infect enemies' drinking water. During the Second World War, Imperial Japan pioneered warheads filled with disease-ridden rats, mice, clothing and fleas which it dropped on Chinese civilians. The disease had been developed at the so-called "Unit 731" facility in northeast China, which was the site of some of Japan's most horrendous war crimes. An estimated 250,000 people were subjected to experimentation at the site. Following the war, both the US and Russia harnessed the technology - much of which was based on Japanese and German research - to use plague as a weapon. Studies have since revealed the USSR focused on developing "aerosolized" forms of the disease - thereby removing the need for it to be transmitted via infected fleas or animals. And despite being a signatory to a convention banning the development of such weapons, Russia was found to still be creating the weapons as late as the 1990s when former USSR microbiologist Ken Alibek defected to the US.

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