Efficacy of an inactivated bivalent vaccine against the prevalent strains of Newcastle disease and H9N2 avian influenza
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RESEARCH
Open Access
Efficacy of an inactivated bivalent vaccine against the prevalent strains of Newcastle disease and H9N2 avian influenza Jing Zhao1, Huiming Yang1, Hongjun Xu2, Zengbin Ma1 and Guozhong Zhang1*
Abstract Background: Newcastle disease (ND) and avian influenza subtype H9N2 (H9N2 AI) are two of the most important diseases of poultry, causing severe economic losses in the global poultry industry. Vaccination is an effective way to prevent and control the spread of ND virus (NDV) and H9N2 AI virus (AIV), but the antigenic differences between the current circulating strains and the vaccine strains might account for recent ND and H9N2 AI outbreaks in vaccinated poultry flocks. Methods: We developed an inactivated bivalent H9N2 and NDV vaccine based on the current prevalent strains of H9N2 AIV and NDV in China and evaluated its efficacy in chickens in this study. Results: The results indicated that the inactivated bivalent vaccine could induce a fast antibody response in vaccinated chickens. The hemagglutination inhibition (HI) titer in the sera increased rapidly, and the highest HI titer was observed at 4 weeks post-vaccination (wpv) with a mean titre of 8.6 log2 for NDV and 9.5 log2 for H9N2. Up until 15 wpv, HI titers were still detectable at a high level of over 6 log2. The immunized chickens showed no signs of disease after challenge at 3 wpv with the prevalent strains of NDV and H9N2 AIV isolated in 2012–2014. Moreover, viral shedding was completely inhibited in vaccinated chickens after challenge with H9N2 AIV and inhibited by at least 90% with NDV compared to the controls at 5dpc. Conclusions: Our findings suggest that the inactivated NDV and H9N2 vaccine induces a fast and strong antibody response in vaccinated chickens and is efficacious in poultry against NDVs and H9N2 AIVs. Keywords: Newcastle disease virus, H9N2 avian influenza virus, Inactivated vaccine, Efficacy, Chicken
Background Newcastle disease virus (NDV) and avian influenza virus (AIV) are two of the most important pathogens in poultry worldwide [1]. Newcastle disease (ND) is usually caused by virulent NDV, which can result in 100% mortality in many species of birds [2]. The H9N2 low pathogenic avian influenza viruses have been circulating worldwide in multiple avian species, resulting in great economic losses owing to reduced egg production or increased mortality associated with coinfection with other pathogens [3–6]. Thus, severe economic losses in the poultry industry * Correspondence: [email protected] 1 Key Laboratory of Animal Epidemiology and Zoonoses;, Ministry of Agriculture, College of Veterinary Medicine, China Agricultural University, No.2 Yuanmingyuan West Road, Haidian District, Beijing 100193, People’s Republic of China Full list of author information is available at the end of the article
caused by NDV and AIV highlight the importance of vaccine improvement and development. In China, the implementation of extensive vaccination programs in commercial poultry farms has reduced the number of epizootic outbreaks of
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