Scientists have discovered a new type of botox they believe is the “deadliest substance known to man” and have withheld the DNA sequence because an antidote is not known.

It is the first time the scientific community has made such a move to withhold such information but security concerns have dictated that they do so.

New Scientist reports that just 2 billionths of a gram, or inhaling 13 billionths of a gram, of the protein botulinum produced by the soil bacterium Clostridium botulinum will kill an adult.

The toxin blocks the release of acetylcholine, the chemical secreted by nerves that makes muscles work. People who accidentally ingest it, as can happen when the bacteria grows in food, develop botulism and often die of paralysis.

Victims are treated with antibodies that are produced artificially and react with the seven families of botulinum – named A to G – discovered so far.

Stephen Arnon and colleagues at the California Department of Public Health in Sacramento reported this week that they have found an eighth toxin – type H – in the feces of a child who had the typical symptoms of botulism.

“Because no antitoxins as yet have been developed to counteract the novel C. Botulinum toxin, the authors had detailed consultations with representatives from numerous appropriate US government agencies,” editors of the Journal of Infectious Diseases said.

Japanese cult Aum Shinrikyo tried to release Botulinum in downtown Tokyo in the 1990s.

This story originally appeared on News.com.au.