<Tr> <Th> NCBI </Th> <Td> proteins </Td> </Tr> <P> Botulinum toxin (BTX) is a neurotoxic protein produced by the bacterium Clostridium botulinum and related species . It prevents the release of the neurotransmitter acetylcholine from axon endings at the neuromuscular junction and thus causes flaccid paralysis . Infection with the bacterium causes the disease botulism . The toxin is also used commercially in medicine, cosmetics and research . </P> <P> Botulinum is the most acutely lethal toxin known, with an estimated human median lethal dose (LD) of 1.3--2.1 ng / kg intravenously or intramuscularly and 10--13 ng / kg when inhaled . </P> <P> There are eight types of botulinum toxin, named type A--H. Type A and B are capable of causing disease in humans, and are also used commercially and medically . Types C--G are less common; types E and F can cause disease in humans, while the other types cause disease in other animals . Type H is considered the deadliest substance in the world--an injection of only 2 - billionths of a gram (2 ng) can cause death to an adult . Botulinum toxin types A and B are used in medicine to treat various muscle spasms and diseases characterized by overactive muscle . The commercial form is marketed under the brand name Botox, among others . </P>

What is the most toxic substance to humans