Abstract
Although Newcastle disease virus (NDV) with high pathogenicity has frequently been isolated in poultry in China since 1948, the mode of its transmission among avian species remains largely unknown. Given that various wild bird species have been implicated as sources of transmission, in this study we genotypically and pathotypically characterized 23 NDV isolates collected from chickens, ducks, and pigeons in live bird markets (LBMs) in South China as part of an H7N9 surveillance program during December 2013–February 2014. To simulate the natural transmission of different kinds of animals in LBMs, we selected three representative NDVs—namely, GM, YF18, and GZ289—isolated from different birds to evaluate the pathogenicity and transmission of the indicated viruses in chickens, ducks, and pigeons. Furthermore, to investigate the replication and shedding of NDV in poultry, we inoculated the chickens, ducks, and pigeons with 106 EID50 of each virus via intraocular and intranasal routes. Eight hour after infection, the naïve contact groups were housed with those inoculated with each of the viruses as a means to monitor contact transmission. Our results indicated that genetically diverse viruses circulate in LBMs in South China's Guangdong Province and that NDV from different birds have different tissue tropisms and host ranges when transmitted in different birds. We therefore propose the continuous epidemiological surveillance of LBMs to support the prevention of the spread of these viruses in different birds, especially chickens, and highlight the need for studies of the virus–host relationship.
Highlights
Due to its high morbidity and mortality, Newcastle disease (ND) is considered to be the most significant and widespread infectious disease in commercial poultry—one that can cause severe economic losses in poultry, chickens, and affect a range of other domestic species, including ducks and pigeons (Sinkovics and Horvath, 2000; Office International Des Epizooties (OIE), 2012)
Newcastle disease virus (NDV) strains are categorized as highly virulent, moderately virulent, or avirulent, all according to pathogenicity for chickens gauged by the intracerebral pathogenicity index (ICPI) and mean death time (MDT; OIE, 2012)
NDV strains have been divided into two major divisions—class I and class II—which contribute to the extensive genetic diversity among poultry worldwide, with class I being further divided into nine genotypes distributed worldwide in waterfowls and class II comprising 18 (I–XVIII) genotypes when the sequences are isolated over time (Ballagi-Pordány et al, 1996; Liu et al, 2003; Kim et al, 2007; Miller et al, 2010; Diel et al, 2012; OIE, 2012; Snoeck et al, 2013)
Summary
Due to its high morbidity and mortality, Newcastle disease (ND) is considered to be the most significant and widespread infectious disease in commercial poultry—one that can cause severe economic losses in poultry, chickens, and affect a range of other domestic species, including ducks and pigeons (Sinkovics and Horvath, 2000; OIE, 2012). In 1948, genotype IX emerged as a unique group including the first virulent NDV strains (F48E9) in South China, and members of the genotype are occasionally isolated from a wild variety of bird species (Liu et al, 2003). Many newly emergent strains isolated from a wide range of birds contribute to increasing the global burden of NDV and cause enormous losses in the poultry industry (Liu et al, 2003; Jinding et al, 2005; Kim et al, 2007; Kang et al, 2014). Genotype VII of NDV strains have continued to circulate in poultry throughout South China and are considered to be enzootic as they spread around the globe
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