Clostridium botulinum toxin acts by:

Ans. c (Blocking Ach release at synapses & NMJ). (Ref. Harrison's, 18th/ Chapter 141. Botulism; KDT 5th/76)BOTULISM (Food-borne botulism, Wound botulism, Intestinal botulism).Pathogenesis:# Of the eight distinct toxin types described (A, B, Cl, C2, D, E, F, and G), all except C2 are neurotoxins\# C2 is a cytotoxin of unknown clinical significance.# Toxin types A, B, E, and (rarely) F cause human disease; type G (from C. argentinense) has been associated with sudden death, but not with neuroparalytic illness.# Botulinum neurotoxin, whether ingested, inhaled, or produced in the intestine or a wound, enters the vascular system and is transported to peripheral cholinergic nerve terminals, including -- Neuromuscular junctions,- Postganglionic parasympathetic nerve endings, and- Peripheral ganglia.- The central nervous system is not involved.# The edrophonium chloride (Tensilon) test for myasthenia gravis may be falsely positive in botulism but is usually less dramatically positive than in the former condition.# The steps involved in neurotoxin activity include:- Specific binding to presynaptic nerve cells at the myoneural junction,- Internalization of the toxin inside the nerve cell in endocytic vesicles,- Translocation of the toxin into the cytosol, and- Proteolysis by toxin (a zinc endopeptidase) of components of the neuroexocytosis apparatus curtailing release of the neurotransmitter acetylcholine.- Cure follows sprouting of new nerve terminals.Treatment:# Neither the use of antibiotics to eliminate an intestinal source for possible continued toxin production nor the administration of guanidine hydrochloride and other drugs to reverse paralysis is of proven value.# After testing for hypersensitivity to horse serum, antitoxin is given# Rx of infant botulism requires supportive care and administration of human botulism immune globulin.# A pentavalent vaccine (A-E) is available for use in highly exposed individuals.Also remember:BOTULINUM TOXIN may be a treatment used:# For achalasia# For anal fissure# For dystonia# For essential tremor# For gastroparesis,# For Tourette syndrome# As bioterrorism agent# For Frey's syndrome Botulinum toxin type A has been approved for the treatment of strabismus, blepharospasm, cervical dystonia, and glabellar lines.Botulinum toxin type B has been approved for the treatment of cervical dystonia.