Host innate immune responses of ducks infected with Newcastle disease viruses of different pathogenicities

Though previous studies have identified two strains of duck-origin Newcastle disease virus (NDV) with varying levels of pathogenicity, the relationship between the early-phase host innate immune response and pathogenesis of ducks infected with these strains in the lungs and thymuses remains unclear. In this study, we compared the viral distribution and mRNA expression of immune-related genes in ducks following infection with two NDV strains, Duck/CH/GD/SS/10 (SS-10) and Duck/CH/GD/NH/10 (NH-10). Both NDV strains replicated systemically in tested tissues (i.e., small intestine, cecal tonsils, brain, lung, bursa of Fabricius, thymus, and spleen) and exhibited different biological properties in duck pathogenicity. Real-time quantitative polymerase chain reaction showed that the expression of TLR3, TLR7, RIG-I, MDA5, IL-1β, IL-2, IL-6, IL-8, IFN-alpha, IFN-beta, IFN-gamma in the lungs was significantly greater than in the respective thymus genes during the early post infection stage. However, in the lungs, the expression of TLR3, TLR7, IL-1β, IL-2, IL-8, IFN-alpha, IFN-gamma, and MHC II induced by SS-10 at 72 h post-inoculation (hpi) was less than with NH-10. Furthermore, the expression of IL-6 and IFN-beta in the lungs and thymuses following infection with SS-10 was greater than that with NH-10 at 24 and 48 hpi. These results highlight important differences in host innate immune responses, courses of infection, and pathogenesis following NDV infection. Further studies should work to expand understandings of the molecular mechanisms related to NDV infection

Phylogenetic and pathotypic characterization of Newcastle disease viruses circulating in South China and transmission in different birds

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 h 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

Continuing Reassortant of H5N6 Subtype Highly Pathogenic Avian Influenza Virus in Guangdong

First identified in May 2014 in China’s Sichuan Province, initial cases of H5N6 avian influenza virus (AIV) infection in humans raised great concerns about the virus’s prevalence, origin, and development. To evaluate both AIV contamination in live poultry markets (LPMs) and the risk of AIV infection in humans, we have conducted surveillance of LPMs in Guangdong Province since 2013 as part of environmental sampling programs. With environmental samples associated with these LPMs, we performed genetic and phylogenetic analyses of 10 H5N6 AIVs isolated from different cities of Guangdong Province from different years. Results revealed that the H5N6 viruses were reassortants with hemagglutinin (HA) genes derived from clade 2.3.4.4 of H5-subtype AIV, yet neuraminidase (NA) genes derived from H6N6 AIV. Unlike the other seven H5N6 viruses isolated in first 7 months of 2014, all of which shared remarkable sequence similarity with the H5N1 AIV in all internal genes, the PB2 genes of GZ693, GZ670, and ZS558 more closely related to H6N6 AIV and the PB1 gene of GZ693 to the H3-subtype AIV. Phylogenetic analyses revealed that the environmental H5N6 AIV related closely to human H5N6 AIVs isolated in Guangdong. These results thus suggest that continued reassortment has enabled the emergence of a novel H5N6 virus in Guangdong, as well as highlight the potential risk of highly pathogenic H5N6 AIVs in the province

Reassortment of Avian Influenza A/H6N6 Viruses from Live Poultry Markets in Guangdong, China

Since early 2013, H7N9-subtype avian influenza virus (AIV) has caused human infection in eastern China. To evaluate AIV contamination and the public risk of infection, we systematically implemented environmental sampling from live poultry markets in Guangdong Province. Through real-time polymerase chain reaction assays and next-generation sequencing, we generated full nucleotide sequences of all 10 H6N6 AIVs isolated during sampling. Focusing on sequence analyses of hemagglutinin genes of the 10 H6N6 AIVs revealed that the viruses were low pathogenic AIVs with the typical hemagglutinin cleavage site of P-Q-I-E-T-R-G. The hemagglutinin, neuraminidase, and nucleocapsid genes of nine AIVs were of ST2853-like (H6-subtype) lineage, ST192-like (N6-subtype) lineage, and HN573-like (H6-subtype) lineage, respectively; whereas the other five genes were of ST339-like (H6-subtype) lineage. However, the polymerase PB2 and nucleocapsid genes of one strain (HZ057) were of GS/GD-like (H5N1-subtype) and ST339-like lineages. Phylogenic analysis revealed that all eight genes of the 10 viruses belonged to Eurasian avian lineage. Altogether, the 10 AIVs were reassortants of different genetic groups of exchanges with the same virus subtype, thus illustrating the genetic diversity and complexity of H6N6-subtype AIVs in Guangdong Province