LONDON (Reuters) - Two British citizens are critically ill after they were exposed to Novichok, the same nerve agent that struck down a former Russian agent and his daughter in March, Britain’s top counter-terrorism officer said.
What do we know, and not know, so far?
The Novichok group of poisons was first developed by the Soviet Union in the 1970s and 80s.
There are several variants of Novichok, a binary weapon containing two less toxic chemicals that when mixed react to produce a poison several times more lethal than sarin or VX.
Russia’s ambassador to Britain, Alexander Yakovenko, has identified the alleged poison as Novichok A-234, derived from an earlier version known as A-232.
Nerve agents like Novichok disrupt and halt many of the human body’s essential processes, including breathing.
Novichok does this by blocking an enzyme called acetylcholinesterase, which regulates messages down nerves and at junctions between nerves and muscles. It can cause paralysis, convulsions, vomiting and the partial or total collapse of bodily functions. In fatal cases, death can be due to asphyxiation or cardiac arrest.
“The consequences of being exposed to a nerve agent include the risk of heart attack and damage to the brain through poor oxygenation,” said Alastair Hay, a professor of environmental toxicology at Britain’s Leeds University.
“Breathing will likely have been seriously impaired, both through the failure of normal muscle action and the secretion of fluids into the lungs,” he added.
The ambulance service was called at 0915 GMT on Saturday to an address in Muggleton Road, Amesbury, seven miles (11 km) north of Salisbury, where Sergei Skripal and his daughter Yulia were found poisoned in March.
At the Amesbury address, a 44-year-old woman had collapsed. At 1430 GMT the ambulance service was called back to same address where a 45-year-old man was ill.
Both are in critical condition at Salisbury District Hospital.
Initially, it was thought they had overdosed on contaminated heroin or crack cocaine but by Monday there were concerns over their symptoms and samples were sent to the Porton Down military laboratory.
Neil Basu, Britain’s most senior counter-terrorism officer, said the samples showed the pair — named by British media as Dawn Sturgess and Charlie Rowley — had been exposed to the nerve agent Novichok.
British Prime Minister Theresa May has accused Russia of poisoning former double agent Skripal and his daughter Yulia with Novichok. Russia has repeatedly denied involvement.
“Following the detailed analysis of these samples, we can confirm that the man and woman have been exposed to the nerve agent Novichok, which has been identified as the same nerve agent that contaminated both Yulia and Sergei Skripal,” Basu said.
Skripal and his daughter were found unconscious on a bench outside The Maltings shopping centre in Salisbury on March 4.
After weeks of treatment at Salisbury District Hospital, Yulia was discharged in April and Sergei in May.
She told Reuters in May: “My life has been turned upside down. We are so lucky to have both survived this attempted assassination. Our recovery has been slow and extremely painful.”
Both the Skripals now reside at a secret location.
Mystery surrounds the poisonings.
The motive for attacking an aged Russian traitor who was exchanged in a Kremlin-approved spy swap is still unclear.
The logic of using such an exotic nerve agent, which has overt links to Russia’s Soviet past, is also unclear, though British security sources have suggested it may have been used to send a signal to the opponents of the Kremlin.
Russian officials have said that if Novichok had been deployed by a state-sponsored hit squad then thousands would have died in Salisbury, including the Skripals.
It is also unclear where the Novichok came from, who deployed it and, after the most recent poisoning, how much of it is left in and around Salisbury.
Health chiefs said the risk to the public was low, repeating their earlier advice given after the Skripals were taken ill that the public should wash their clothes and use cleansing wipes on personal items.
But the nature of the Novichok group of agents means it does not decompose quickly.
“They are designed to be quite persistent — they hang around in the environment, neither evaporating or decomposing quickly,” said Andrea Sella, professor of inorganic chemistry at UCL.
“While the public at large are at very low risk from this material, until the source is found there is a remote chance that someone else might come into contact with it.”
Police have cordoned off at least five different areas, including a park and a property in Salisbury, and a pharmacy and a Baptist church community centre in Amesbury, although health chiefs said the risk to the public was low.
Reporting by Guy Faulconbridge and Kate Kelland; Editing by Catherine Evans