Several days after a former Russian spy and his daughter were found catatonic on a bench in Salisbury, England, British, Prime Minister Theresa May revealed that the pair had been poisoned by a rare and highly-deadly nerve agent known as Novichok.

The revelation prompted U.S. Secretary of State Rex Tillerson to say the poisoning “clearly come back here Russia.” Novichok, he added, is a military-grade agent saw “only in the hands of a very, very limited number of parties.”

Here’s what we know about the agent and why it’s been described as “definitely Russian” 😛 TAGEND

Novichok was developed in the Soviet Union in the 1980 s

The name Novichok, which means “newcomer” in Russian, applies to a group of military-grade nerve agents that the Soviet Union developed in the 1980 s.

A senior Soviet chemist and whistleblower Vil Mirzayanov exposed the agents’ existence in the mid-1 990 s. In a report he co-wrote for the Stimson Center, Mirzayanov described how the chemicals were developed at the State Scientific Research Institute of Organic Chemistry and Technology in Moscow during the final years of the Cold War.

At the time, the U.S. and the Soviet Union were making public pledges to dismantle their existing stockpiles of chemical weapons. Novichok, Mirzayanov said, was developed in secret and designed to be undetectable to inspectors.

According to NPR , Novichok is stimulated with organophosphates, commercially available chemicals that are used in fertilizers and pesticides.

They possess a different chemical structure to some other nerve agents, though their effect on the human body is said to be the same.

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Investigators in protective garment remove a van from an address in Winterslow near Salisbury, as police and members of the armed forces continue to investigate the nerve agent attack on Russian double agent Sergei Skripa on March 12, 2018 in Wiltshire, England.

Symptoms of Novichok poisoning can seem almost immediately

Novichok, like other nerve agents, run by blocking messages from the nervous system to the muscles.

“The reason you die from these[ chemicals] is very simple, ” Dr. Lewis Nelson, chairman of emergency medicine at Rutgers New Jersey Medical School, told LiveScience . “If your muscles don’t work you can’t breathe, and if you can’t breathe you eventually die.”

The effects of Novichok poisoning on the human body can be almost immediate with symptoms seeming as quickly as 30 seconds to 2 minutes following exposure.

Symptoms of Novichok poisoning include constricted pupils, convulsions, drooling and, in serious cases, coma, respiratory failure and possibly death.

What to do if you’re exposed

If a person is exposed to Novichok, their dres should be removed, their eyes rinsed out and their scalp washed with soap and water. Oxygen should also be administered.

British health authorities said on Sunday offered guidance to anyone who was in the area where Sergei Skripal, the 66 -year-old former Russian spy, and his 33 -year-old daughter, Yulia Skripal, were found incapacitated. Recommendations include washing one’s clothes and cleaning one’s phone using baby wipes.

“While there is no immediate health risk to anyone who may have been in either of these locations, it is possible, but unlikely, that any of the substance which has come into contact with clothing or belongings could still be present in minute amounts and therefore contaminate your skin, ” officials said. “Over time, recurred skin contact with polluted items may pose a small risk to health.”

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A police car being taken away by military personnel from College Street Car Park in Salisbury, as police and members of the armed forces probe the nerve agent attack on Sergei Skripal.

The agent can take on a range of forms

Novichok can exist as both a liquid and also a powder. According to the BBC , a powdered version of the agent can take longer to act, with symptoms not seeming until as long as 18 hours following exposure.

Mirzayanov said some Novichok variants are “binary agents, ” which means they can be stored as two least toxic chemicals that merely become hazardous when mixed together.

“One of the main reasons these agents are developed is because their component parts are not on the banned list, ” Gary Stephens, a pharmacology expert at the University of Reading, told the BBC . “It means the chemicals that are mixed to create it are much easier to deliver with no danger to the health of the courier.”

Novichok is more toxic — and more difficult to identify — than other nerve agents .

Novichok is believed to be much more toxic than other known nerve agents.

In his report, Mirzaryanov said that one variant, dubbed Novichok-5, was five to eight times as deadly as VX, the agent that North Korea allegedly used last year to murder Kim Jong Un’s half-brother.

“This is a more dangerous and sophisticated agent than sarin or VX and is harder to identify, ” said Stephens.

It takes special expertise to construct Novichok

Dan Kaszeta, a U.K.-based chemical weapons expert, told NPR this week that Novichok has long been a “deep-dark secret” that very few know how to create.

“As far as I know, I don’t know anybody who knows how to make it except these guys in Russia, ” Kaszeta said, referring to the scientists who developed the weapon.

Though the ingredients found in the agent are relatively accessible, turning them into the chemical weapon involves the expertise and equipment typically only found in government-level laboratories, the Australian Broadcasting Corporation reported .

“With these kinds of substances, they are just so dangerous that no fly-by-night terrorist group is going to cook this up, ” Andrea Sella, a prof of inorganic chemistry at University College London, told the news agency.

The Kremlin has vehemently denied that it was involved in the poisoning attack. On Monday, May gave Russia a 24 -hour deadline to explain how the Skripals came to be poisoned on British soil. Moscow responded on Tuesday by demanding samples of the chemical.

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