Influences of major histocompatibility complex class I haplotypes on avian influenza virus disease traits in Thai indigenous chickens

Natural infections with influenza viruses have been reported in a variety of animal species including humans, pigs, horses, sea mammals, mustelids and birds. Occasionally, devastating pandemics occur in domestic chickens (broiler and layers) and in humans. From November 2003 to March 2004 in many countries in Asia, there were outbreaks of H5N1 avian influenza virus, causing death of infected patients, and devastating the poultry industry. Some groups of Thai indigenous chickens survived and were therefore classified as resistant. These traits were related to immunogenetics, in particular, the major histocompatibility complex (MHC) class I and class II molecules. The chicken MHC class I were investigated as candidate genes for avian influenza virus disease resistance. Seven hundred and thirty Thai indigenous chickens from smallholder farms in the rural area of avian influenza virus disease outbreaks in the central part of Thailand were used in the present study. They were separated into two groups, 340 surviving chickens and 390 dead chickens (resistant and susceptible). Genomic DNA were precipitated from blood samples and feathers. The DNA were used to amplify the MHC class I gene. Data were analyzed using chi square analysis to test significant differences of influences of MHC class I haplotypes on avian influenza virus disease traits. The results represented nine MHC class I haplotypes: A1, B12, B13, B15, B19, B21, B2, B6, and BA12, and included 10 of their heterozygotes. The homozygous B21 from these collected samples had a 100% survival rate and they were the major survival group. In addition, the heterozygous B21 also had a high survival rate because of co-dominant expression of these genes. In contrast, the homozygous B13 had a 100% mortality rate and they were the major mortality group. These results confirmed that MHC class I haplotypes influence avian influenza virus disease-resistant traits in Thai indigenous chicken. The MHC genes can be used as genetic markers to improve disease-resistant traits in chicken.