Abstract
H5N1 highly pathogenic avian influenza (HPAI) was one of the most important avian diseases in poultry production of China, especially in Guangdong province. In recent years, new H5N1 highly pathogenic avian influenza viruses (HPAIV) still emerged constantly, although all poultry in China were immunized with H5N1 vaccinations compulsorily. To better understand the pathogenicity and transmission of dominant clades of the H5N1 HPAIVs in chicken from Guangdong in 2012, we chose a clade 7.2 avian influenza virus named A/Chicken/China/G2/2012(H5N1) (G2) and a clade 2.3.2.1 avian influenza virus named A/Duck/China/G3/2012(H5N1) (G3) in our study. Our results showed that the chickens inoculated with 103 EID50 of G2 or G3 viruses all died, and the titers of virus replication detected in several visceral organs were high but different. In the naive contact groups, virus shedding was not detected in G2 group and all chickens survived, but virus shedding was detected in G3 group and all chickens died. These results showed that the two clades of H5N1 HPAIVs had high pathogenicity in chickens and the contact transmission of them was different in chickens. The results of cross reactive HI assay showed that antigens of G2 and G3 were very different from those of current commercial vaccines isolates (Re-4, Re-6, and D7). And to evaluate the protective efficacy of three vaccines against most isolates form Guangdong belonging to clade 2.3.2.1 in 2012, G3 was chosen to challenge the three vaccines such as Re-4, Re-6, and D7. First, chickens were immunized with 0.3 ml Re-4, Re-6, and D7 inactivated vaccines by intramuscular injection, respectively, and then challenged with 106 EID50 of G3 on day 28 post-vaccination. The D7 vaccine had 100% protection against G3 for chickens, the Re-6 vaccine had 88.9%, and the Re-4 vaccine only had 66.7%. Our results suggested that the D7 vaccine could prevent and control H5N1 virus outbreaks more effectively in Guangdong. From the above, it was necessary to conduct continuously epidemiological survey and study the pathogenicity and antigenic variation of avian influenza in Southern China.
Highlights
Influenza A viruses are the most important pathogen of three types (A, B, and C) of influenza viruses, to both the poultry industry and human health
According to antigenic characteristics by the WHO, the HA gene of G2 belonged to clade 7.2, and that of G3 belonged to clade 2.3.2.1 (Figure 1). Their HA genes had a series of basic amino acids at the cleavage site of the HA (-RRRKR/GLF-), which represents the high pathogenicity of the H5N1 AIVs in poultry (Gohrbandt et al, 2011)
The first H5N1 highly pathogenic avian influenza virus (HPAIV) in China was isolated from sick geese in Guangdong province in 1996 (Xu et al, 1999)
Summary
Influenza A viruses are the most important pathogen of three types (A, B, and C) of influenza viruses, to both the poultry industry and human health. In 2002, a new H5N1 HPAI outbreak in Hong Kong infected millions of birds, including several types of wild water fowl. This was the first time the H5N1 HPAIV was found to infect water fowl (Lee et al, 2005; Nguyen et al, 2005). Between 2003 and 2005, the H5N1 HPAI repetitively broke out in East Asia and South Asia, and even spread to Europe and Africa This resulted in more than 150 million birds dead or slaughtered and 53 human fatalities (SturmRamirez et al, 2004; World Health Organization, 2005). Since 2003, the H5N1 HPAI had continued influencing more than 60 states or areas including Laos, Vietnam, Thailand, Hong Kong, and China (World Health Organization, 2013b). H5N1 HPAIVs are zoonotic etiological agents recognized as a severe threat to both the poultry industry and human public health around the world
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