Influences of MHC class II haplotypes on avian influenza traits in Thai indigenous chicken

Natural infections with influenza viruses have been reported in a variety of animal species including human, pigs, horses, sea mammals, mustelids and birds. Occasionally devastating pandemics occur in domestic chickens (broiler and layers) and human. During November 2003 to March 2004 in many countries in Asia, there are outbreaks of H5Nl avian influenza virus, causing of death of infected patients and devastated poultry industry. Some groups of Thai indigenous chickens are survivable recommended as resistance. These traits were related to immunogenetics, especially, the major histocompatibility complex (MHC) class I and class II molecules. The chicken MHC class II was investigated as candidate genes for avian influenza resistance. Seven hundred and thirty Thai indigenous chickens of small holder farms in the rural area of avian influenza outbreaks in the central part of Thailand were used in this study. They were separated into two groups, 340 survivable chickens and 390 dead chickens (resistance and susceptible). Genomic DNA were precipitated from blood samples and feathers. Diluted DNA was amplified to identify MHC haplotype. Data were statistically analyzed by chi-square analysis to test significant differences of influences of MHC class II haplotypes on avian influenza traits. The results represented ten MHC class II haplotypes, A9, B12, B13, B14, B19, B21, B2, B4, B5, and B6, and included eighteen of their crossbred. The homozygous B21 from these collected samples had 100 percent of survival rate and they were the major survival group. In addition, the heterozygous B21 also showed high survival rate because of co-dominant expression of these genes. In the other way, the homozygous B 13 had 100 percent of mortality rate and they were the major group of high mortality rate. These results confirmed that MHC class II haplotypes influenced on avian influenza resistant traits in Thai indigenous chicken. The MHC genes can be used as genetic markers to improve disease resistant traits in chicken.