VMC 311: Systematic Veterinary Bacteriology and Mycology (2+1)

ANTIGENS AND TOXINS

C.botulinum possesses a number of H, O and spore antigens

• Eight types of C.botulinum have been identified (Types A to G) based on the immunological difference in the toxins produced by them.
• These neurotoxins are identical in pharmacological action but differ in potency, distribution and antigenicity.
• They are neutralized only by the homologus antiserum.

Type	Toxin produced	Most susceptible animals	Sources of toxin	Disease
A	A	Humans, chickens, pigs	Vegetables, fruits, meat and fish	Food borne botulism
Cα	C1	Waterfowl	Invertebrate carcases, rotting vegetation and material on refuse dumps	Limberneck in long necked birds
Cβ	C2	Cattle, horses, mink, dogs	Carcases, baled silage, chicken manure as feed supplement	Forage poisoning
D	D	Cattle, sheep	Eating contaminated bones and carcases of small mammals (Phosphorus deficiency-Pica)	Lamsiekte

• The toxins differ from other exotoxins in that it is not released during the life of the organism.
• It is appears in the medium only on the death and autolysis of the cell.
• It is believed to be synthesized initially as a nontoxic protoxin or progenitor toxin.
• Trypsin and other enzymes activate progenitor toxin to active toxin.
• The toxin is heat labile and its mol.wt. is 70,000.
• One mg of neurotoxins contains more than 120 million mouse lethal doses.
• The lethal dose for human is 1-2μg. This toxin acts slowly taking several hours to kill.

Comparison of the toxins of C.tetani and C.botulinum

	C.tetani	C.botulinum
Site of toxin production	Wounds	Carcases, decaying vegetation and occasionally wounds and intestine
Mode of action	Centrally by blocking synaptic inhibition	Peripherally by blocking neuromuscular transmission
Type of paralysis	Spastic paralysis	Flaccid paralysis
Antigenic types of toxin	Tetanospasmin (one antigenic type)	Eight different toxins produced by types A-G