The objective of this study are to conduct a case-control Genome-Wide Association Study to identify genomic regions that differ between survivors vs their age and genetic-matched controls, determine whether the same genetic regions affect survival to HPAI in three genetic varieties of commercial layer chickens, and whether the same genetic regions affect survival to H7N3 and H5N2 strains of HPAI.
Identifying any genetic differences would be extremely valuable because it will enable the breeding HPAI resistant chickens. Additionally, this on-going project may provide information on specific genes that vaccinations can target or are best targeted for gene editing.
Scientists working on this project include: Dr. Anna Wolc, assistant professor in department of animal science at Iowa State University and geneticist at Hy-Line Int.; Dr. Jack Dekkers, professor in department of animal science at Iowa State University; Dr. Wioleta Drobik, assistant professor at Warsaw University of Life Sciences; and Dr. Janet Fulton, Molecular Geneticist, Hy-Line International.
Highly Pathogenic Avian Influenza (HPAI) strains have resulted in significant economic losses to the poultry egg production industry. The 2015 H5N2 HPAI outbreak in the US resulted in losses due to mortality or mandated euthanization of over 50 million hens. With cooperation from several commercial egg producers, blood samples were obtained from rare survivors of different commercial egg production varieties within production facilities in the US mid-west. Samples were also obtained from birds that had survived following an H7N3 HPAI outbreak in Mexico. DNA was isolated from these blood samples and also from non-affected birds of the same commercial varieties. Variation in the DNA was compared between the survivors and their controls using a chip that detects variation in 600,000 DNA positions simultaneously. Statistical analysis of the DNA differences was done to determine if there was any relationship between these DNA differences and the ability to survive HPAI, either H5N2 in the US or H7N3 in Mexico.
Analysis of the DNA from the HPAI challenge survivors from both H5N2 and H7N3 viruses showed that there is genetic influence on survival, with 20% of the survival of the birds being due to genetics. This indicates that it should be possible to improve resistance to HPAI infection by selection. Furthermore, specific regions of the DNA were shown to influence survival to HPAI. This provides an opportunity to identify which genes may be involved with resistance, providing specific targets for genetic selection. However, the results from the two virus strains did not show the same genetic regions being involved, showing that there is neither a single gene or a small number of genes involved with the resistance. This complicates the process of selection for improved resistance, as it suggests that different selection would be needed for resistance to different viruses.
Further research is ongoing with these samples, in collaboration with Dr. Jacqueline Smith of the Roslin Institute in Scotland, who will be sequencing these samples to improve the resolution of the genetic variation being identified. Additional samples of survivor hens and their progeny will also be analyzed.