Efficacy studies on Haemophilus gallinarum bacterin preparations

Area of Science:

• Veterinary immunology
• Bacteriology
• Poultry health

Background:

• Haemophilus gallinarum causes significant economic losses in poultry.
• Serotype A strains are prevalent, necessitating effective vaccination strategies.
• Previous vaccine formulations have shown variable efficacy.

Purpose of the Study:

• To evaluate the efficacy of inactivated Haemophilus gallinarum bacterins against homologous and heterologous challenge.
• To compare the protective potential of thimerosal- and formalin-inactivated bacterins.
• To assess the effectiveness of a bivalent bacterin.

Main Methods:

• Chickens were immunized with broth cultures inactivated by thimerosal or formalin.
• Vaccination protocols included single or double doses.
• Inactivated bacterins were tested for efficacy against challenge inoculation with two serotype A strains of H. gallinarum.
• A bivalent bacterin was also evaluated.

Main Results:

• The two tested serotype A strains of H. gallinarum did not provide cross-protection, even within the same serotype.
• A single dose of thimerosal-inactivated bacterin conferred protection against homologous challenge.
• Two doses of formalin-inactivated bacterin were necessary for protection.
• The bivalent bacterin demonstrated good protection against one strain but not the other at a single dose.

Conclusions:

• Vaccine efficacy against Haemophilus gallinarum is strain-specific.
• Inactivation methods and dosage regimens significantly influence bacterin effectiveness.
• Further research is needed to develop broadly protective vaccines against H. gallinarum serotype A.