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Reducing The Risk of Avian Influenza Outbreaks by Increasing Genetic Resistance in Chickens

Ewald, Sandra; Toro, Haroldo
Auburn University
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The long term goal of this project is to reduce the risk of avian influenza (AI) outbreaks by increasing genetic resistance in the chicken population. We hypothesize that as in other species, the Mx gene limits AI viral replication and/or disease outbreaks in chickens, thus genetic stocks can be selected for increased resistance against AI. The specific aims of the proposed research are:

  1. Determine if embryo fibroblasts cultures differing in Mx genotype differ in susceptibility to infection with low pathogenic AI strains (LPAI).
  2. Determine whether commercial chickens having the antiviral Mx allele are resistant to challenge with different LPAI viruses.
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Non-Technical Summary - Avian Influenza causes enormous economical losses to the poultry industry. In addition outbreaks of highly-pathogenic AI have occurred in humans in various Asian countries as result from transmission from AI affected chickens. In mice and humans, one of the Mx proteins is induced in cells by RNA viruses through the interferon-alpha and -beta pathways, and inhibits replication of influenza virus.We propose herein to determine if birds differing in Mx genotype differ in susceptibility to infection with AI virus

Approach - Obj. 1. In vitro studies of AI virus replication in cells of the three Mx genotypes (Mx+/+, +/- and -/-) will be conducted with chicken embryo fibroblast (CEF) cultures established from individual embryonated chicken eggs (ECE). CEF will be infected with virus (dose to be determined) in the presence of acetylated trypsin as described by Garber et al. (4), who demonstrated that AI strain A/Turkey/Wisconsin68 (H5N9) replicates in CEF. These authors also showed that CEF transfected to express mouse Mx1 protein were resistant to the same AI virus. CEF transfected to express mouse Mx1 constitutively (4) produced many fewer (500-fold) and smaller plaques than untransfected CEF cultures at the viral dose used. Virus yields, determined by plating the supernatant fluids from infected CEF with or without mouse Mx1 expression onto susceptible CEF, revealed that Mx1 expression reduced viral yield by more than 3 orders of magnitude. Obj. 2.Evaluate chickens from a commercial line for Mx allele associations with resistance or susceptibility to AI challenge. Chicks in the study will be typed for Mx 631 dimorphism and challenged with LPAI. Because we expect no mortality or severe disease symptoms from these AI strains, we will evaluate duration and severity of infection by 3 criteria:

  1. Viral persistence in the respiratory and intestinal tract.
  2. Histopathological changes and histomorphometry of the nasal and tracheal mucosa.
  3. Specific antibody response.
Persistence of virus in the respiratory and intestinal tract will be determined by virus re-isolation attempts. We expect more efficient clearance of the virus and either faster recovery or less damage in the respiratory tract epithelium/mucosa in Mx+ birds.
Funding Source
Nat'l. Inst. of Food and Agriculture
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Bacterial Pathogens
Risk Assessment, Management, and Communication
Meat, Poultry, Game