A Study on the Prevalence and Virulence of Avian Influenza A (H5N1, H5N6 and H7N9) Viruses on Poultry at Lang Son Markets in Vietnam

Abstract

Abstract:In 2014 and 2015, composite cloacal and tracheal swab samples of poultry sold at markets in Lang Son province (Vietnam) were collected in order to examine the circulation of avian influenza A (H5N1, H5N6 and H7N9) viruses. The results show that: (i) for the chicken illegally imported from China, 3.93% to 6.43% of the chickens were found positive with type A, 3.18% to 3.78% were positive with subtype H5, and 0.37% to 3.40% were positive with subtype N1 viruses; (ii) for the chicken sold at local markets, 15.55% were found positive with type A, 5% were positive with subtype H5, and 2.77% were positive with subtype N1 viruses; (iii) for the chicken sold at the border markets, 13.49% were positive with type A, 4.76% were positive with subtype H5, and 3.96% were positive with subtype N1 viruses; (iv) for the chicken and ducks sold at the border markets with avian influenza A viruses (H5N6), 10.4% to 36.1% were positive with type A; 4.1% to 6.25% were positive with subtype H5; and 2.3% to 6.25% were found positive with subtype N6 viruses; (v) subtype H7N9 were not prevalent on the poultry sold at the border and local markets; and (vi) laboratory chicken for testing IVPI (Intravenous Pathogenicity Index) showed symptoms of sickness and died within one to two days after infected with H5N1 and H5N6 viruses. The IVPI ranged from 2.9 to 2.92. This shows that the avian influenza virus strains isolated in Lang Son were highly virulent (HPAI).