Submitted to: Avian Diseases
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/12/2002
Publication Date: 6/5/2003
Citation: Beck, J.R., Swayne, D.E., Davison, S., Casavant, S., Gutierrez, C. 2003. Validation Of Egg Yolk Antibody Testing As A Method To Determine Influenza Status In White Leghorn Hens. Avian Diseases 47:867-71, 2003. Interpretive Summary: The avian influenza (AI) status of chicken flocks is determined by testing blood serum for antibodies against the virus and is important for certifying eggs and egg products for export. However, this method is cumbersome and labor intensive because it requires handling of individual birds. As an alternative test method, we infected egg laying chickens with mildly pathogenic H7N2 AI virus and examined egg yolks as a source of antibodies against influenza virus. Antibodies against influenza were detected in the egg yolks of the infected chickens. This method can be substituted for blood serum testing to certify AI free status of a flock for export of eggs and egg products.
Technical Abstract: Determination of the avian influenza (AI) status of a flock has traditionally been done by detection of serum antibodies. However, for many diseases, detection of antibodies in egg yolk has been effective in monitoring disease status of laying flocks. This study compared the utility of egg yolk verses serum for determining AI status in laying hen flocks. Specific-pathogen-free white leghorn hens were inoculated via respiratory tract with an H7N2 mildly pathogenic AI virus or sterile allantoic fluid, or subcutaneously with an inactivated oil emulsion vaccine produced from the same AI virus or normal allantoic fluid. Antibody levels were determined by using the agar gel immunodiffusion (AGID) test, the hemagglutination inhibition (HI) test and the enzyme-linked immunosorbent assay (ELISA). Anti-influenza antibodies were detected in sera of all live virus inoculated hens by day 7 post-inoculation (PI) (AGID and ELISA tests), but detection of antibodies in egg yolk was delayed by a few days, with all being positive by day 14 PI. Sera from all vaccinated hens were positive by day 14 PI (AGID and ELISA tests) and egg yolk was positive by day 18 PI. The HI test was less sensitive than the ELISA and AGID tests in detecting anti-influenza antibodies in both sera and yolk. Serum and yolk from all control birds remained negative throughout the study. These studies show that currently used serological tests can detect antibodies in serum and yolk samples from hens exposed to live AI virus or from those that have been vaccinated. Antibody is detected earlier in the serum than in the yolk, and earlier from a bird exposed to a live infection than from a vaccinated bird.