The vaccination-challenge trial: the gold standard test to evaluate the protective efficacy of infectious coryza vaccines.
Infectious coryza is an upper respiratory tract disease of chickens with the major impact occurring in multi-age flocks. We investigated the relationship between the level of antibodies, as detected by a haemagglutination-inhibition (HI) assay, in infectious coryza-vaccinated chickens and the protection against challenge in those chickens. In one experiment, chickens given a single dose of either of two infectious coryza vaccines lacked a detectable HI response to vaccination but showed significant levels of protection 11 weeks after vaccination. In contrast, in chickens given two doses of an infectious coryza vaccine and challenged 3 weeks after the second vaccine dose, there was a strong serological response with 36/40 birds having a HI titre of 1/20 or greater. In this trial there was an apparent relationship between titre and subsequent protection, with none of the 32 chickens with a titre of 1/40 or 1/80 showing any clinical signs and only one of the same group yielding the challenge organism on culture. In contrast, three of the four vaccinated chickens with a HI titre less than 1/5 developed the typical clinical signs of coryza and yielded the challenge organism on culture. Overall, our results suggest that HI titres cannot be regarded as a definitive predictor of vaccine efficacy. We suggest that the vaccination-challenge trial is the gold standard for the evaluation of the immune response to infectious coryza vaccines.
García
A
A
Laboratorios Avilab, Porcicultores 80 Tepatitlan, Jalisco, México.
Romo
F
F
Ortiz
A M
AM
Blackall
P J
PJ
D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D002645:Chickens; D010850:Picornaviridae Infections / Q000517:prevention & control / Q000662:veterinary*; D011201:Poultry Diseases / Q000517:prevention & control* / Q000821:virology; D012229:Rhinovirus / Q000276:immunology*; D014765:Viral Vaccines / Q000276:immunology*
D000914:Antibodies, Viral; D014765:Viral Vaccines