A toxoid is a protein toxin, which has been denatured (by e.g. heat or chemical treatment) and has, therefore, lost its toxicity. A toxoid retains, however, its antigenic properties and can, therefore, be used in vaccines.
Toxoids are toxins without toxic activity that can elicit an immune response, that is, antibodies (see above for explanation). Toxoids can be produced by chemical inactivation of the native toxin or by manipulations of the gene encoding the toxin so that the toxin is inactivated.The main advantage of toxoids is that they are safer than the disease-associated toxin. Toxoids administered parenterally elicit antibodies (IgM and IgG).
TOXOID VACCINES:
- Both gram negative and gram-positive bacteria produce exotoxins. Exotoxins can be inactivated by formaldehyde, iodine, other chemical or heat treatment and form toxoid.
- Toxoid is immunogenic without toxic effects. Toxoid vaccines have been used for tetanus, anthrax etc.
- Some veterinary vaccines combine both toxoid and killed bacteria by formalizing the whole culture and this is called anaculture. These types of vaccines are available for clostridial diseases. Trypsinization of anaculture makes it more immunogenic.
Advantage: The exotoxin is immunogenic and the whole organism can be avoided.
Disadvantage: Only effective if diseases caused solely by bacterial exotoxins.
The tetanus vaccine is a solution of tetanus toxoid.