VMC 221: Veterinary Immunology and Serology (1+1)

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 formalinizing 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 whole organism can be avoided.
• Disadvantage: Only effective if diseases caused solely by bacterial exotoxins.

Bacterins

• Bacterins are the vaccines containing killed bacteria. This is usually done with formal dehyde and adjuvant like aluminiam hydroxide or alum is added to increase its immunogenicity.
• Autogenous vaccines are prepared using the organism from the infected animal itself or from other infected animals in the same farm after inactivation with formal dehyde and found successful to control diseases. For example fowl cholera vaccine.

• Advantages:
  • Easy to prepare
  • No reversion to virulence
• Disadvantages:
  • Immunity is short lasting (usually less than six months)