Evaluation and Attempted Optimization of Avian Embryos and Cell Culture Methods for Efficient Isolation and Propagation of Low Pathogenicity Avian Influenza Viruses

Characterization of highly pathogenic avian influenza virus in retail dairy products in the US

In March 2024, clade 2.3.4.4b H5N1 highly pathogenic avian influenza virus (HPAIV) was detected in dairy cattle in the US, and it was discovered that the virus could be detected in raw milk. Although affected cow's milk is diverted from human consumption and current pasteurization requirements are expected to reduce or eliminate infectious HPAIV from the milk supply, a study was conducted to characterize whether the virus could be detected by quantitative real-time RT-PCR (qrRT-PCR) in pasteurized retail dairy products and, if detected, to determine whether the virus was viable. From 18 April to 22 April 2024, a total of 297 samples of Grade A pasteurized retail milk products (23 product types) were collected from 17 US states that represented products from 132 processors in 38 states. Viral RNA was detected in 60 samples (20.2%), with qrRT-PCR-based quantity estimates (non-infectious) of up to 5.4log1050% egg infectious doses per mL, with a mean and median of 3.0log10/mL and 2.9log10/mL, respectively. Samples that were positive for type A influenza by qrRT-PCR were confirmed to be clade 2.3.4.4 H5 HPAIV by qrRT-PCR. No infectious virus was detected in any of the qrRT-PCR-positive samples in embryonating chicken eggs. Further studies are needed to monitor the milk supply, but these results provide evidence that the infectious virus did not enter the US pasteurized milk supply before control measures for HPAIV were implemented in dairy cattle.IMPORTANCEHighly pathogenic avian influenza virus (HPAIV) infections in US dairy cattle were first confirmed in March 2024. Because the virus could be detected in raw milk, a study was conducted to determine whether it had entered the retail food supply. Pasteurized dairy products were collected from 17 states in April 2024. Viral RNA was detected in one in five samples, but infectious virus was not detected. This provides a snapshot of HPAIV in milk products early in the event and reinforces that with current safety measures, infectious viruses in milk are unlikely to enter the food supply.

Duration of Highly Pathogenic Avian Influenza Virus and Newcastle Disease Virus Infectivity in Dried Ornithologic Study Skins

Ornithologic study skins are specimens of avian skins that have been preserved by drying after removing the viscera and muscle. Because of the high value of study skins for scientific studies, specimens are shared among researchers. There is concern that study skins might be contaminated with high-consequence diseases such as highly pathogenic avian influenza virus (HPAIV) or Newcastle disease virus (NDV). To mitigate risk, thermal or chemical treatment of study skins may be required before transfer; however, such treatments might damage the specimens. Therefore, a study was conducted to evaluate the duration of infectivity of HPAIV and NDV in study skins prepared from infected chickens (Gallus gallus). Study skins were prepared from 10 chickens infected with each virus. Skin and feather pulp samples were taken at the time of study skin preparation to establish starting titers. Mean starting titers in the skin was 4.2 log10 and 5.1 log10 50% egg infectious doses (EID50) for HPAIV and NDV groups respectively, and were 6.7 log10 EID50 for HPAIV, and 6.4 log10 EID50 for NDV in feather pulp. Samples were collected at 2 and 4 wk of drying to quantify viable virus. At 2 wk, fewer samples had detectable virus and mean titers were 1.8 log10 (skin) and 2.1 log10 (feathers) EID50 for HPAIV, and 1.7 log10 (skin) and 3.5 log10 (feathers) EID50 for NDV. At 4 wk viable virus could not be detected in either tissue type.

Remote Sensing and Ecological Variables Related to Influenza A Prevalence and Subtype Diversity in Wild Birds in the Lluta Wetland of Northern Chile

The Lluta River is the northernmost coastal wetland in Chile, representing a unique ecosystem and an important source of water in the extremely arid Atacama Desert. During peak season, the wetland is home to more than 150 species of wild birds and is the first stopover point for many migratory species that arrive in the country along the Pacific migratory route, thereby representing a priority site for avian influenza virus (AIV) surveillance in Chile. The aim of this study was to determine the prevalence of influenza A virus (IAV) in the Lluta River wetland, identify subtype diversity, and evaluate ecological and environmental factors that drive the prevalence at the study site. The wetland was studied and sampled from September 2015 to October 2020. In each visit, fresh fecal samples of wild birds were collected for IAV detection by real-time RT-PCR. Furthermore, a count of wild birds present at the site was performed and environmental variables, such as temperature, rainfall, vegetation coverage (Normalized Difference Vegetation Index-NDVI), and water body size were determined. A generalized linear mixed model (GLMM) was built to assess the association between AIV prevalence and explanatory variables. Influenza positive samples were sequenced, and the host species was determined by barcoding. Of the 4349 samples screened during the study period, overall prevalence in the wetland was 2.07% (95% CI: 1.68 to 2.55) and monthly prevalence of AIV ranged widely from 0% to 8.6%. Several hemagglutinin (HA) and neuraminidase (NA) subtypes were identified, and 10 viruses were isolated and sequenced, including low pathogenic H5, H7, and H9 strains. In addition, several reservoir species were recognized (both migratory and resident birds), including the newly identified host Chilean flamingo (Phoenicopterus chilensis). Regarding environmental variables, prevalence of AIV was positively associated with NDVI (OR = 3.65, p < 0.05) and with the abundance of migratory birds (OR = 3.57, p < 0.05). These results emphasize the importance of the Lluta wetland as a gateway to Chile for viruses that come from the Northern Hemisphere and contribute to the understanding of AIV ecological drivers.

Novel Low Pathogenic Avian Influenza H6N1 in Backyard Chicken in Easter Island (Rapa Nui), Chilean Polynesia

Little is known about the prevalence of avian influenza viruses (AIV) in wildlife and domestic animals in Polynesia. Here, we present the results of active AIV surveillance performed during two sampling seasons in 2019 on Easter Island (Rapa Nui). Tracheal and cloacal swabs as well as sera samples were obtained from domestic backyard poultry, while fresh faeces were collected from wild birds. In addition to detecting antibodies against AIV in 46% of the domestic chickens in backyard production systems tested, we isolated a novel low pathogenic H6N1 virus from a chicken. Phylogenetic analysis of all genetic segments revealed that the virus was closely related to AIV’s circulating in South America. Our analysis showed different geographical origins of the genetic segments, with the PA, HA, NA, NP, and MP gene segments coming from central Chile and the PB2, PB1, and NS being closely related to viruses isolated in Argentina. While the route of introduction can only be speculated, our analysis shows the persistence and independent evolution of this strain in the island since its putative introduction between 2015 and 2016. The results of this research are the first evidence of AIV circulation in domestic birds on a Polynesian island and increase our understanding of AIV ecology in region, warranting further surveillance on Rapa Nui and beyond.

Neuropathology of feral conures with bromethalin toxicosis

Bromethalin is a widely used neurotoxic rodenticide sometimes affecting nontarget wildlife. However, the effects of bromethalin on avian species are largely unknown. Here, we report the neuropathology of 14 feral conures (Psittacara sp.) with bromethalin toxicosis. Clinically, all birds presented with different degrees of paraparesis that sometimes progressed to dysphagia, ataxia, and tetraparesis. Histologically, there was astrogliosis, pallor, and vacuolation of white matter in the brain. This was usually more prominent in the medial longitudinal fasciculus, pons, optic tectum, cerebellar peduncle, and ventral funiculus. In most affected areas, there was loss of oligodendrocytes, and axons had extensive myelin loss or marked intramyelinic edema with splitting of myelin sheaths at the intraperiod line. Conures with bromethalin toxicosis had neuropathological changes similar to those of mammals exposed to bromethalin but with a characteristic distribution, probably related to higher susceptibility to cytotoxic edema in certain regions of the avian brain.

Simple Method for Establishing Primary Leporidae Skin Fibroblast Cultures

Commercial hare and rabbit immortalized cell lines are extremely limited regarding the many species within the lagomorpha order. To overcome this limitation, researchers and technicians must establish primary cell cultures derived from biopsies or embryos. Among all cell types, fibroblasts are plastic and resilient cells, highly convenient for clinical and fundamental research but also for diagnosis, particularly for viral isolation. Here, we describe a fast and cheap method to produce primary fibroblast cell cultures from leporid species, using dispase II, a protease that allows dermal-epidermal separation, followed by a simple enzymatic digestion with trypsin. This method allows for the establishment of an in vitro cell culture system with an excellent viability yield and purity level higher than 85% and enables the maintenance and even immortalization of leporid fibroblastic cells derived from tissues already differentiated.

In Vitro Viral Evolution Identifies a Critical Residue in the Alphaherpesvirus Fusion Glycoprotein B Ectodomain That Controls gH/gL-Independent Entry

Herpesvirus entry and spread requires fusion of viral and host cell membranes, which is mediated by the conserved surface glycoprotein B (gB). Upon activation, gB undergoes a major conformational change and transits from a metastable prefusion to a stable postfusion conformation. Although gB is a structural homolog of low-pH-triggered class III fusogens, its fusion activity depends strictly on the presence of the conserved regulatory gH/gL complex and nonconserved receptor binding proteins, which ensure that fusion occurs at the right time and space. How gB maintains its prefusion conformation and how gB fusogenicity is controlled remain poorly understood. Here, we report the isolation and characterization of a naturally selected pseudorabies virus (PrV) gB able to mediate efficient gH/gL-independent virus-cell and cell-cell fusion. We found that the control exerted on gB by the accompanying viral proteins is mediated via its cytosolic domain (CTD). Whereas gB variants lacking the CTD are inactive, a single mutation of a conserved asparagine residue in an alpha-helical motif of the ectodomain recently shown to be at the core of the gB prefusion trimer compensated for CTD absence and uncoupled gB from regulatory viral proteins, resulting in a hyperfusion phenotype. This phenotype was transferred to gB homologs from different alphaherpesvirus genera. Overall, our data propose a model in which the central helix acts as a molecular switch for the gB pre-to-postfusion transition by conveying the structural status of the endo- to the ectodomain, thereby governing their cross talk for fusion activation, providing a new paradigm for herpesvirus fusion regulation.

Adaptation and characterization of Anatid herpesvirus 1 in different permissible cell lines

Duck viral enteritis is an acute, contagious infection of Anatidae family members. The disease is caused by Anatid herpesvirus 1 (AnHV-1). The infection of AnHV-1 is controlled by vaccination to the flock with chick embryo adapted attenuated vaccine in developed countries. However, its economic impact in developing countries is substantial and there is a need to understand the cell culture spectrum of the virus to produce its vaccine on a mass scale. In the present study, the permissivity of AnHV-1 for different cells was analyzed. The AnHV-1 showed enhanced replication following its serial passage in CEF, DF-1, Vero, MDCK, and QT-35 cells. The characteristic cytopathic effect (CPE) of rounding and clumping of cells were observed in CEF, DF-1, Vero, and QT-35 cell lines. The infectivity and viral replication were highest in CEF, DF-1, Vero, and QT-35 cells. In contrast, the results suggested that MDCK cells are less permissive for AnHV-1 infection with negligible CPE and reduced viral replication. Heterologous cell culture systems other than chicken embryo fibroblasts to adapted live vaccine viruses will provide a system devoid of other avian infectious agents. Moreover, it can be used for the propagation and cultivation of AnHV-1 vaccine strain for developing cell culture-based vaccines with high titer and could be an economical alternative for the existing options.

Avian Influenza Virus Isolation, Propagation, and Titration in Embryonated Chicken Eggs

Avian influenza virus and some mammalian influenza A viruses can be isolated, propagated, and titrated in embryonated chicken eggs (ECEs). Most sample types can be accommodated in ECE culture with appropriate processing. Isolation may also be accomplished in cell culture, and if a mammalian lineage influenza A is expected to be in an avian sample, for example swine influenza in turkey specimens, mammalian cell may be preferable. Culture in ECEs is highly sensitive but is not specific for influenza A, which may be an advantage because a sample may be screened for several agents at once. Once an agent is isolated in culture, the presence of influenza viruses can be confirmed by hemagglutination inhibition assay, antigen immunoassay, agar gel immunodiffusion assay, or RT-PCR. Finally, ECEs may be used to propagate and titrate an avian influenza virus.

Evaluation of host systems for efficient isolation and propagation of duck Tembusu virus

Several phylogenetic clusters of duck Tembusu virus (DTMUV) that caused outbreaks in ducks in Asia have been identified since its emergence in 2010, highlighting the need for an efficient host system that can support isolation of all circulating phylogenetic clusters of DTMUV. In this study, various host systems, including different avian embryonated eggs (duck and chicken) and cell cultures (primary duck embryo fibroblast (DEF), primary chicken embryo fibroblast (CEF), baby hamster kidney (BHK-21), African green monkey kidney (Vero) and Aedes albopictus clone C6/36 (C6/36) cells), were evaluated and compared for their ability to support DTMUV isolation and propagation. Our results showed that all host systems were susceptible to DTMUV infection; however, BHK-21 and primary DEF cells supported more efficient replication of DTMUV compared to the other host systems. BHK-21 cells had the highest DTMUV isolation rate when tested with experimental and field clinical samples. All circulating phylogenetic clusters of DTMUV, including clusters 1, 2 and 3, were successfully isolated from duck clinical samples using BHK-21 cells. In conclusion, our findings supported the use of BHK-21 cells as a host system for primary isolation of all circulating phylogenetic clusters of DTMUV from duck clinical samples. This study highlights the importance of selecting the most appropriate host system for efficient isolation and propagation of DTMUV from duck clinical samples.RESEARCH HIGHLIGHTS DTMUV replicated more efficiently in BHK-21 and primary DEF cells than in other host systems tested.BHK-21 cells had the highest DTMUV isolation rate.All DTMUV phylogenetic clusters were successfully isolated from the samples using BHK-21 cells.BHK-21 cells were the most efficient host system for DTMUV isolation.

Equine-Like H3 Avian Influenza Viruses in Wild Birds, Chile

Since their discovery in the United States in 1963, outbreaks of infection with equine influenza virus (H3N8) have been associated with serious respiratory disease in horses worldwide. Genomic analysis suggests that equine H3 viruses are of an avian lineage, likely originating in wild birds. Equine-like internal genes have been identified in avian influenza viruses isolated from wild birds in the Southern Cone of South America. However, an equine-like H3 hemagglutinin has not been identified. We isolated 6 distinct H3 viruses from wild birds in Chile that have hemagglutinin, nucleoprotein, nonstructural protein 1, and polymerase acidic genes with high nucleotide homology to the 1963 H3N8 equine influenza virus lineage. Despite the nucleotide similarity, viruses from Chile were antigenically more closely related to avian viruses and transmitted effectively in chickens, suggesting adaptation to the avian host. These studies provide the initial demonstration that equine-like H3 hemagglutinin continues to circulate in a wild bird reservoir.

Cell Cultures for Virology: Usability, Advantages, and Prospects

Virus detection in natural and clinical samples is a complicated problem in research and diagnostics. There are different approaches for virus isolation and identification, including PCR, CRISPR/Cas technology, NGS, immunoassays, and cell-based assays. Following the development of genetic engineering methods, approaches that utilize cell cultures have become useful and informative. Molecular biology methods allow increases in the sensitivity and specificity of cell cultures for certain viruses and can be used to generate reporter cell lines. These cell lines express specific reporter proteins (e.g., GFP, luciferase, and CAT) in response to virus infection that can be detected in a laboratory setting. The development of genome editing and synthetic biology methods has given rise to new perspectives regarding the design of virus reporter systems in cell cultures. This review is aimed at describing both virology methods in general and examples of the development of cell-based methods that exist today.

Insertion of Basic Amino Acids in the Hemagglutinin Cleavage Site of H4N2 Avian Influenza Virus (AIV)-Reduced Virus Fitness in Chickens is Restored by Reassortment with Highly Pathogenic H5N1 AIV

Highly pathogenic (HP) avian influenza viruses (AIVs) are naturally restricted to H5 and H7 subtypes with a polybasic cleavage site (CS) in hemagglutinin (HA) and any AIV with an intravenous pathogenicity index (IVPI) ≥ 1.2. Although only a few non-H5/H7 viruses fulfill the criteria of HPAIV; it remains unclear why these viruses did not spread in domestic birds. In 2012, a unique H4N2 virus with a polybasic CS ³²²PEKRRTR/G³²⁹ was isolated from quails in California which, however, was avirulent in chickens. This is the only known non-H5/H7 virus with four basic amino acids in the HACS. Here, we investigated the virulence of this virus in chickens after expansion of the polybasic CS by substitution of T³²⁷R (³²²PEKRRRR/G³²⁹) or T³²⁷K (³²²PEKRRKR/G³²⁹) with or without reassortment with HPAIV H5N1 and H7N7. The impact of single mutations or reassortment on virus fitness in vitro and in vivo was studied. Efficient cell culture replication of T³²⁷R/K carrying H4N2 viruses increased by treatment with trypsin, particularly in MDCK cells, and reassortment with HPAIV H5N1. Replication, virus excretion and bird-to-bird transmission of H4N2 was remarkably compromised by the CS mutations, but restored after reassortment with HPAIV H5N1, although not with HPAIV H7N7. Viruses carrying the H4-HA with or without R³²⁷ or K³²⁷ mutations and the other seven gene segments from HPAIV H5N1 exhibited high virulence and efficient transmission in chickens. Together, increasing the number of basic amino acids in the H4N2 HACS was detrimental for viral fitness particularly in vivo but compensated by reassortment with HPAIV H5N1. This may explain the absence of non-H5/H7 HPAIV in poultry.

Coupling metabolomics analysis and DOE optimization strategy towards enhanced IBDV production by chicken embryo fibroblast DF-1 cells

Infectious bursal disease (IBD) caused by IBD virus (IBDV) is highly contagious viral and vaccination in chicken embryo has been an effective mean to prevent acute infection. However, the current production of IBDV vaccine faces serious batch instability and external contamination. The chicken embryonic fibroblast cell line DF-1 is widely used for the proliferation of avian viruses and vaccine production. Thus, optimizing the production of IBDV by DF-1 cells has an important application value. Combining metabolomics analysis and a Design of Experiments (DOE) statistical strategy, this study successfully optimized the process of IBDV production by DF-1 cells. Differential analysis and time series analysis of metabolite data in both IBDV-infected and uninfected DF-1 cells were performed by multivariate statistical analysis. The results showed that the intracellular metabolite intensities of glycolysis, the pentose phosphate pathway, the nucleoside synthesis pathway, lipid metabolism, and glutathione metabolism were upregulated, and the TCA cycle underwent a slight downregulation after IBDV infection of DF-1 cells. Based on the metabolome results and DOE statistical optimization method, the additive components suitable for IBDV proliferation were determined. The IBDV titer increased by 20.7 times upon exogenous addition of cysteine, methionine, lysine and nucleosides in the control medium, which is consistent with the predicted result (20.0 times) by a multivariate quadratic equation. This study provides a strategy for the efficient production of IBDV vaccines and could potentially be utilized to improve the production of other viral vaccines and biologics.

Assessment of replicate numbers for titrating avian influenza virus using dose-response models

Embryonating chicken eggs (ECEs) are among the most sensitive laboratory host systems for avian influenza virus (AIV) titration, but ECEs are expensive and require space for storage and incubation. Therefore, reducing ECE use would conserve resources. We utilized statistical modeling to evaluate the accuracy and precision of AIV titration with 3 instead of 5 ECEs for each dilution by the Reed-Muench method for 50% endpoint calculation. Beta-Poisson and exponential dose-response models were used in a simulation study to evaluate observations from actual titration data from 18 AIV isolates. The reproducibility among replicates of a titration was evaluated with one AIV isolate titrated in 3 replicates with the beta-Poisson, exponential, and Weibull dose-response models. The standard deviation (SD) of the error between input and estimated virus titers was estimated with Monte Carlo simulations using the fitted dose-response models. Good fit was observed with all models that were utilized. Reducing the number of ECEs per dilution from 5 to 3 resulted in the width of the 95% confidence interval increasing from ±0.64 to ±0.75 log₁₀ 50% ECE infectious doses (EID₅₀) and the SD of the error increased by 0.03 log₁₀ EID₅₀. Our study suggests that using fewer ECEs per dilution is a viable approach that will allow laboratories to reduce costs and improve efficiency.

Recovery of influenza A viruses from lake water and sediments by experimental inoculation

Influenza A viruses (IAV) are zoonotic pathogens relevant to human, domestic animal and wildlife health. Many avian IAVs are transmitted among waterfowl via a faecal-oral-route. Therefore, environmental water where waterfowl congregate may play an important role in the ecology and epidemiology of avian IAV. Water and sediment may sustain and transmit virus among individuals or species. It is unclear at what concentrations waterborne viruses are infectious or remain detectable. To address this, we performed lake water and sediment dilution experiments with varying concentrations or infectious doses of four IAV strains from seal, turkey, duck and gull. To test for infectivity of the IAV strains in a concentration dependent manner, we applied cultivation to specific pathogen free (SPF) embryonated chicken eggs and Madin-Darby Canine Kidney (MDCK) cells. IAV recovery was more effective from embryonated chicken eggs than MDCK cells for freshwater lake dilutions, whereas, MDCK cells were more effective for viral recovery from sediment samples. Low infectious dose (1 PFU/200 μL) was sufficient in most cases to detect and recover IAV from lake water dilutions. Sediment required higher initial infectious doses (≥ 100 PFU/200 μL).

Medium optimization based on comparative metabolomic analysis of chicken embryo fibroblast DF-1 cells

Chicken embryo fibroblast DF-1 cells are increasingly being used in the production of avian virus vaccines. However, the relatively low proliferative capacity does not meet the requirements of industrial production. In this study, we attempted to improve the proliferative capacity of DF-1 cells. The results of intracellular metabolomics showed that 28 types of metabolites could play roles in DF-1 cell growth based on the variance and timing analysis of intracellular metabolites from DF-1 cells grown in two media with distinct growth difference, DMEM/F12 (1 : 1) and DMEM. By examining the differences in the components in the two media, DOE was used to screen and optimize the growth medium for DF-1 cells. The maximum cell density was 40.72% higher, and the infectious bursal disease virus (IBDV) titer was 2.68 times higher, in the optimized medium than in the control. This study proposes a complete solution from metabolomics to media optimization.

This study proposes a medium optimal method based on DOE methodology and metabolomics of chicken embryo fibroblasts DF-1 cells.

Wild birds in Chile Harbor diverse avian influenza A viruses

While the circulation of avian influenza viruses (IAV) in wild birds in the northern hemisphere has been well documented, data from South America remain sparse. To address this gap in knowledge, we undertook IAV surveillance in wild birds in parts of Central and Northern Chile between 2012 and 2015. A wide diversity of hemagglutinin (HA) and neuraminidase (NA) subtypes were identified and 16 viruses were isolated including low pathogenic H5 and H7 strains, making this the largest and most diverse collection of Chilean avian IAVs to date. Unlike IAVs isolated from wild birds in other South American countries where the genes were most like viruses isolated from wild birds in either North America or South America, the Chilean viruses were reassortants containing genes like viruses isolated from both continents. In summary, our studies demonstrate that genetically diverse avian IAVs are circulating in wild birds in Chile highlighting the need for further investigation in this understudied area of the world.

Assessment of pathogenicity and antigenicity of American lineage influenza H5N2 viruses in Taiwan

During December 2003 and March 2004, large scale epidemics of low-pathogenic avian influenza (LPAI) H5N2 occurred in poultry farms in central and southern Taiwan. Based on genomic analysis, these H5N2 viruses contain HA and NA genes of American-lineage H5N2 viruses and six internal genes from avian influenza A/H6N1 viruses endemic in poultry in Taiwan. After disappearing for several years, these novel influenza H5N2 viruses caused outbreaks in poultry farms again in 2008, 2010 and 2012, and have evolved into high pathogenic AI (HPAI) since 2010. Moreover, asymptomatic infections of influenza H5N2 were detected serologically in poultry workers in 2012. Therefore, we evaluated antigenicity and pathogenicity of the novel H5N2 viruses in ferrets. We found that no significant antigenic difference was detected among the novel H5N2 viruses isolated from 2003 to 2014 and the novel H5N2 viruses could cause mild infections in ferrets. Monitoring zoonotic transmission of the novel H5N2 viruses is necessary.

The Length of N-Glycans of Recombinant H5N1 Hemagglutinin Influences the Oligomerization and Immunogenicity of Vaccine Antigen

Hemagglutinin glycoprotein (HA) is a principle influenza vaccine antigen. Recombinant HA-based vaccines become a potential alternative for traditional approach. Complexity and variation of HA N-glycosylation are considered as the important factors for the vaccine design. The number and location of glycan moieties in the HA molecule are also crucial. Therefore, we decided to study the effect of N-glycosylation pattern on the H5 antigen structure and its ability to induce immunological response. We also decided to change neither the number nor the position of the HA glycosylation sites but only the glycan length. Two variants of the H5 antigen with high mannose glycosylation (H5_hm) and with low-mannose glycosylation (H5_Man5) were prepared utilizing different Pichia strains. Our structural studies demonstrated that only the highly glycosylated H5 antigen formed high molecular weight oligomers similar to viral particles. Further, the H5_hm was much more immunogenic for mice than H5_Man5. In summary, our results suggest that high mannose glycosylation of vaccine antigen is superior to the low glycosylation pattern. Our findings have strong implications for the recombinant HA-based influenza vaccine design.

Investigation of a mortality cluster in wild adult yellow-eyed penguins (Megadyptes antipodes) at Otago Peninsula, New Zealand

We investigated an epidemic mortality cluster of yellow-eyed penguins (Megadyptes antipodes) that involved 67 moribund or dead birds found on various beaches of the Otago Peninsula, New Zealand, between 21 January and 20 March 2013. Twenty-four carcases were examined post-mortem. Histological lesions of pulmonary, hepatic and splenic erythrophagocytosis and haemosiderosis were found in 23 of 24 birds. Fifteen birds also had haemoglobin-like protein droplets within renal tubular epithelial cells. Despite consistent histological lesions, a cause of death could not be established. Virology, bacteriology and molecular tests for avian influenza, avian paramyxovirus-1, avipoxvirus, Chlamydia psittaci, Plasmodium spp., Babesia spp., Leucocytozoon spp. and Toxoplasma gondii were negative. Tissue concentrations of a range of heavy metals (n = 4 birds) were consistent with low level exposure, while examination of proventricular contents and mucus failed to detect any marine biotoxins or Clostridium botulinum toxin. Hepatic concentrations of total polycyclic aromatic hydrocarbons (PAHs) (n = 5 birds) were similar to background concentrations of polycyclic aromatic hydrocarbons previously found in yellow-eyed penguins from the South Island of New Zealand, but there were significantly higher concentrations of 1-methylnapthelene and 2-methylnapthelene in the birds found dead in this mortality cluster. The biological significance of this finding is unclear. A temporal investigation of the epidemic did not indicate either a common source or propagative epidemic pattern. Although our investigation did not definitively implicate a toxic or infectious agent, we could not rule out causes such as toxic marine organisms or mycoplasmosis. Further investigations should therefore by carried out in the event of future mortality clusters.

Macrophages from disease resistant B2 haplotype chickens activate T lymphocytes more effectively than macrophages from disease susceptible B19 birds

Resistance to respiratory pathogens, including coronavirus-induced infection and clinical illness in chickens has been correlated with the B (MHC) complex and differential ex vivo macrophage responses. In the current study, in vitro T lymphocyte activation measured by IFNγ release was significantly higher in B2 versus B19 haplotypes. AIV infection of macrophages was required to activate T lymphocytes and prior in vivo exposure of chickens to NP AIV plasmid enhanced responses to infected macrophages. This study suggests that the demonstrated T lymphocyte activation is in part due to antigen presentation by the macrophages as well as cytokine release by the infected macrophages, with B2 haplotypes showing stronger activation. These responses were present both in CD4 and CD8 T lymphocytes. In contrast, T lymphocytes stimulated by ConA showed greater IFNγ release of B19 haplotype cells, further indicating the greater responses in B2 haplotypes to infection is due to macrophages, but not T cells. In summary, resistance of B2 haplotype chickens appears to be directly linked to a more vigorous innate immune response and the role macrophages play in activating adaptive immunity.

A prime/boost vaccination with HA DNA and Pichia-produced HA protein elicits a strong humoral response in chickens against H5N1

Highly pathogenic avian influenza viruses cause severe disease and huge economic losses in domestic poultry and might pose a serious threat to people because of the high mortality rates in case of an accidental transmission to humans. The main goal of this work was to evaluate the immune responses and hemagglutination inhibition potential elicited by a combined DNA/recombinant protein prime/boost vaccination compared to DNA/DNA and protein/protein regimens in chickens. A plasmid encoding hemagglutinin (HA) from the A/swan/Poland/305-135V08/2006 (H5N1) virus, or the recombinant HA protein produced in Pichia pastoris system, both induced H5 HA-specific humoral immune responses in chickens. In two independent experiments, anti-HA antibodies were detected in sera collected two weeks after the first dose and the response was enhanced by the second dose of a vaccine, regardless of the type of subunit vaccine (DNA or recombinant protein) administered. The serum collected from chickens two weeks after the second dose was characterized by three types of assays: indirect ELISA, hemagglutination inhibition (HI) and a diagnostic test based on H5 antibody competition. Although the indirect ELISA failed to detect superiority of any of the three vaccine regimens, the other two tests clearly indicated that priming of chickens with the DNA vaccine significantly enhanced the protective potential of the recombinant protein vaccine produced in P. pastoris.

Avian H11 influenza virus isolated from domestic poultry in a Colombian live animal market

Live animal markets (LAMs) are an essential source of food and trade in Latin American countries; however, they can also serve as ‘hotbeds' for the emergence and potential spillover of avian influenza viruses (AIV). Despite extensive knowledge of AIV in Asian LAMs, little is known about the prevalence South American LAMs. To fill this gap in knowledge, active surveillance was carried out at the major LAM in Medellin, Colombia between February and September 2015. During this period, overall prevalence in the market was 2.67% and a North American origin H11N2 AIV most similar to a virus isolated from Chilean shorebirds asymptomatically spread through multiple bird species in the market resulting in 17.0% positivity at peak of infection. Phenotypically, the H11 viruses displayed no known molecular markers associated with increased virulence in birds or mammals, had α2,3-sialic acid binding preference, and caused minimal replication in vitro and little morbidity in vivo. However, the Colombian H11N2 virus replicated and transmitted effectively in chickens explaining the spread throughout the market. Genetic similarity to H11 viruses isolated from North and South American shorebirds suggest that the LAM occurrence may have resulted from a wild bird to domestic poultry spillover event. The ability to spread in domestic poultry as well as potential for human infection by H11 viruses highlight the need for enhanced AIV surveillance in South America in both avian species and humans.

Expression of Factor X in BHK-21 Cells Promotes Low Pathogenic Influenza Viruses Replication

A cDNA clone for factor 10 (FX) isolated from chicken embryo inserted into the mammalian cell expression vector pCDNA3.1 was transfected into the baby hamster kidney (BHK-21) cell line. The generated BHK-21 cells with inducible expression of FX were used to investigate the efficacy of the serine transmembrane protease to proteolytic activation of influenza virus hemagglutinin (HA) with monobasic cleavage site. Data showed that the BHK-21/FX stably expressed FX after ten serial passages. The cells could proteolytically cleave the HA of low pathogenic avian influenza virus at multiplicity of infection 0.01. Growth kinetics of the virus on BHK-21/FX, BHK-21, and MDCK cells were evaluated by titrations of virus particles in each culture supernatant. Efficient multicycle viral replication was markedly detected in the cell at subsequent passages. Virus titration demonstrated that BHK-21/FX cell supported high-titer growth of the virus in which the viral titer is comparable to the virus grown in BHK-21 or MDCK cells with TPCK-trypsin. The results indicate potential application for the BHK-21/FX in influenza virus replication procedure and related studies.

Mallard or chicken? Comparing the isolation of avian influenza A viruses in embryonated Mallard and chicken eggs

Background

To date, the most efficient and robust method for isolating avian influenza A viruses (IAVs) is using embryonated chicken eggs (ECEs). It is known that low-pathogenic avian IAVs undergo rapid genetic changes when introduced to poultry holdings, but the factors driving mutagenesis are not well understood. Despite this, there is limited data on the effects of the standard method of virus isolation of avian-derived viruses, that is, whether isolation in ECEs causes adaptive changes in avian IAVs. Eggs from a homologous species could potentially offer an isolation vessel less prone to induce adaptive changes.

Methods

We performed eight serial passages of two avian IAVs isolated from fecal samples of wild Mallards in both ECEs and embryonated Mallard eggs, and hemagglutination assay titers and hemagglutinin sequences were compared.

Results

There was no obvious difference in titers between ECEs and embryonated Mallard eggs. Sequence analyses of the isolates showed no apparent difference in the rate of introduction of amino acid substitutions in the hemagglutinin gene (three substitutions in total in embryonated Mallard eggs and two substitutions in ECEs).

Conclusion

Embryonated Mallard eggs seem to be good isolation vessels for avian IAVs but carry some practical problems such as limited availability and short egg-laying season of Mallards. Our study finds isolation of Mallard-derived avian IAVs in ECEs non-inferior to isolation in embryonated Mallard eggs, but more research in the area may be warranted as this is a small-scale study.

Necrotic Response to Low Pathogenic H9N2 Influenza Virus in Chicken Hepatoma Cells

Background:

Limited knowledge about the molecular mechanism of avian influenza H9N2 virus pathogenicity in birds as well as human hosts has limited the development of effective control against the disease. To overcome this issue detailed understanding of the infectious characteristics of the virus in host cells should be obtained.

Objectives:

In this study we examined the replication kinetics of H9N2 virus in a chicken hepatoma cell line to obtain insight into the pathogenesis of H9N2 viruses.

Materials and Methods:

The kinetic replication of H9N2 influenza virus in chicken hepatoma and fibroblastic cells was studied in the presence and absence of supplemental trypsin. High viral titers observed in liver cells in a short time correlated with the degree of cytopathic effects. To determine whether the ultimate outcome of infection results in programmed cell death, the infected cells were observed by the cell viability assay, DNA fragmentation, caspase cascade activation, and quantified lactate dehydrogenase release.

Results:

The degree of viability was significantly reduced in infected hepatoma cells. Observations of caspase activation and cell DNA laddering in infected cells were not indicative of apoptosis. The infected hepatoma cells released lactate dehydrogenase, which is consistent with cell death by necrosis.

Conclusions:

Taken together, these data reveal that cellular protease of chicken liver cells allows the replication of high yields of H9N2 virus in the absence of trypsin and also cell death in the infected cells is due to necrosis.

Comparative analysis of selected innate immune-related genes following infection of immortal DF-1 cells with highly pathogenic (H5N1) and low pathogenic (H9N2) avian influenza viruses

H5N1 and H9N2 viruses are important causes of avian influenza in China. H5N1 is typically associated with severe to fatal disease in poultry, while H9N2 is usually associated with mild disease. Differences in viral virulence prompted us to investigate whether innate immune responses would be differentially regulated following infection by H5N1 and H9N2 viruses. To address this hypothesis, expression of a panel of innate immune-related genes including IFN-α, IFN-β, Mx1, OASL, ISG12, IFIT5, IRF7, USP18, SST, and KHSRP in immortal DF-1 cells following H5N1 and H9N2 infection was analyzed and compared by real-time quantitative RT-PCR. Cells infected by either virus overall exhibited a similar expression profile for four ISGs (Mx1, OASL, ISG12, and IFIT5), IFN-α, IFN-β, and SST gene. However, two immune-regulatory genes (IRF7 and KHSRP) were not responsive to highly pathogenic H5N1 infection but were strongly up-regulated in DF-1 cells infected with low pathogenic H9N2 infection. The subtype-dependent host response observed in this study offers new insights into the potential roles of IRF7 and KHSRP in control and modulation of the replication and virulence of different subtypes or strains of avian influenza A virus.

Growth and replication of infectious bursal disease virus in the DF-1 cell line and chicken embryo fibroblasts

Infectious bursal disease virus (IBDV) causes a highly contagious disease in young chicks and leads to significant economic losses in the poultry industry. To determine a suitable cell line for IBDV infection, replication, and growth kinetics of the virus, DF-1 cells and chicken embryo fibroblasts (CEF) were used. The population doubling per day (Pd/D) was found to be higher in DF-1 as compared to CEF cells. A suitable time of infection (TOI) was established for increased production of virus and greater infectivity titers. The DF-1 and CEF cells were found to be susceptible to infection by producing marked cytopathic effects (CPEs), and the growth curves of IBDV in DF-1 and CEF cells were evaluated by infectivity assay using tissue culture infectious dose (TCID₅₀). The cytopathic effects of the virus in DF-1 and CEF cells were found to be similar, but higher viral titers were detected in the DF-1 cells as compared to CEF. Thus the DF-1 cell line had a higher growth potential and infectivity, which will be of advantage in vaccine production.

Evaluation of avian influenza serologic and virologic diagnostic methods in wild Anseriformes and Charadriiformes

Evaluation of avian influenza virus (AIV) diagnostic methods, including a nucleoprotein (NP) competitive enzyme-linked immunosorbent assay (c-ELISA), hemagglutination inhibition (HI) test, type A real-time reverse transcription polymerase chain reaction (RRT-PCR), and embryonating chicken egg (ECE) virus isolation (VI), suggested validity of these tests in wild birds comparable to that reported in poultry. This was determined by analyzing the results from experimental inoculation of three species of wild birds with a low-pathogenicity AIV and from field surveillance data. The NP c-ELISA in a high-AIV prevalence setting had 100% diagnostic sensitivity (Se; 95% confidence interval [CI]: 81.5%-100%) and 91% diagnostic specificity (Sp; 95% CI: 70.8%-98.9%) in negative controls compared with the RRT-PCR. In low-AIV prevalence flocks using a > 60% inhibition positivity threshold, relative to the HI test, c-ELISA performed with 90.5% Se (95% CI: 86.2%-93.8%) and 41.2% Sp (95% CI: 38.1%-44.5%). Assessment of HI suggests a titer > or = 8 is a positive test result in wild-bird sera, and using this titer had 83.3% Se (95% CI: 58.6%-96.4%) in experimentally infected birds. The RRT-PCR diagnostic performance compared with VI in cloacal swabs varied over 2-6 days postinoculation, having high Se (83.3%-100%) and Sp (94.1%-100%) with substantial agreement (kappa = 0.8). The cycle thresholds (C(t)) for the RRT-PCR of C(t) < 37 for positivity and C(t) = 37-40 as indeterminate were found to be valid for the species included in this study. In view of the interpretative diagnostic difficulties in heterogeneous populations of wild birds, this evaluation in three species of wild birds and in surveillance data should provide greater confidence in the application of these methods routinely used in poultry.

Avian influenza: virology, diagnosis and surveillance

Avian influenza virus (AIV) is the causative agent of a zoonotic disease that affects populations worldwide with often devastating economic and health consequences. Most AIV subtypes cause little or no disease in waterfowl, but outbreaks in poultry can be associated with high mortality. Although transmission of AIV to humans occurs rarely and is strain dependent, the virus has the ability to mutate or reassort into a form that triggers a life-threatening infection. The constant emergence of new influenza strains makes it particularly challenging to predict the behavior, spread, virulence or potential for human-to-human transmission. Because it is difficult to anticipate which viral strain or what location will initiate the next pandemic, it is difficult to prepare for that event. However, rigorous implementation of biosecurity, vaccination and education programs can minimize the threat of AIV. Global surveillance programs help record and identify newly evolving and potentially pandemic strains harbored by the reservoir host.

Avian influenza virus isolation, propagation, and titration in embryonated chicken eggs

Avian influenza virus and some mammalian influenza A viruses are usually isolated, propagated, and titrated in embryonated chicken eggs (ECE). Most any sample type can be accommodated for culture with appropriate processing. Isolation may also be accomplished in cell culture particularly if mammalian lineage isolates are suspected, for example, swine influenza in turkey specimens. Culture is highly sensitive, but is not specific for influenza A, which may be an advantage because a sample may be screened for several agents at once. Once an agent is isolated in culture, the presence of influenza viruses is confirmed with any of several assays. The methods for propagating virus isolates in ECE are described.

Somatic cells, stem cells, and induced pluripotent stem cells: how do they now contribute to conservation?

More than a decade has now passed since the birth of the first endangered species produced from an adult somatic cell reprogrammed by somatic cell nuclear transfer. At that time, advances made in domestic and laboratory animal species provided the necessary foundation for attempting cutting-edge technologies on threatened and endangered species. In addition to nuclear transfer, spermatogonial stem cell transplantation and induction of pluripotent stem cells have also been explored. Although many basic scientific questions have been answered and more than 30 wild species have been investigated, very few successes have been reported. The majority of studies document numerous obstacles that still need to be overcome to produce viable gametes or embryos for healthy offspring production. This chapter provides an overview of somatic cell and stem cell technologies in different taxa (mammals, fishes, birds, reptiles and amphibians) and evaluates the potential and impact of these approaches for animal species conservation.

Accumulation and inactivation of avian influenza virus by the filter-feeding invertebrate Daphnia magna

The principal mode of avian influenza A virus (AIV) transmission among wild birds is thought to occur via an indirect fecal-oral route, whereby individuals are exposed to virus from the environment through contact with virus-contaminated water. AIV can remain viable for an extended time in water; however, little is known regarding the influence of the biotic community (i.e., aquatic invertebrates) on virus persistence and infectivity in aquatic environments. We conducted laboratory experiments to investigate the ability of an aquatic filter-feeding invertebrate, Daphnia magna, to accumulate virus from AIV-dosed water under the hypothesis that they represent a potential vector of AIV to waterfowl hosts. We placed live daphnids in test tubes dosed with low-pathogenicity AIV (H3N8 subtype isolated from a wild duck) and sampled Daphnia tissue and the surrounding water using reverse transcription-quantitative PCR (RT-qPCR) at 3- to 120-min intervals for up to 960 min following dosing. Concentrations of viral RNA averaged 3 times higher in Daphnia tissue than the surrounding water shortly after viral exposure, but concentrations decreased exponentially through time for both. Extracts from Daphnia tissue were negative for AIV by cell culture, whereas AIV remained viable in water without Daphnia present. Our results suggest daphnids can accumulate AIV RNA and effectively remove virus particles from water. Although concentrations of viral RNA were consistently higher in Daphnia tissue than the water, additional research is needed on the time scale of AIV inactivation after Daphnia ingestion to fully elucidate Daphnia's role as a potential vector of AIV infection to aquatic birds.

Avian influenza: mixed infections and missing viruses

A high prevalence and diversity of avian influenza (AI) viruses were detected in a population of wild mallards sampled during summer 2011 in California, providing an opportunity to compare results obtained before and after virus culture. We tested cloacal swab samples prior to culture by matrix real-time PCR, and by amplifying and sequencing a 640bp portion of the hemagglutinin (HA) gene. Each sample was also inoculated into embryonated chicken eggs, and full genome sequences were determined for cultured viruses. While low matrix Ct values were a good predictor of virus isolation from eggs, samples with high or undetectable Ct values also yielded isolates. Furthermore, a single passage in eggs altered the occurrence and detection of viral strains, and mixed infections (different HA subtypes) were detected less frequently after culture. There is no gold standard or perfect reference comparison for surveillance of unknown viruses, and true negatives are difficult to distinguish from false negatives. This study showed that sequencing samples prior to culture increases the detection of mixed infections and enhances the identification of viral strains and sequences that may have changed or even disappeared during culture.

Prevalence and characterization of influenza viruses in diverse species in Los Llanos, Colombia

While much is known about the prevalence of influenza viruses in North America and Eurasia, their prevalence in birds and mammals in South America is largely unknown. To fill this knowledge gap and provide a baseline for future ecology and epidemiology studies, we conducted 2 years of influenza surveillance in the eastern plains (Los Llanos) region of Colombia. Real-time reverse transcriptase polymerase chain reaction (RT-PCR) identified influenza viruses in wild birds, domestic poultry, swine and horses. Prevalence ranged from 2.6% to 13.4% across species. Swine showed the highest prevalence and were infected primarily with 2009 pandemic H1N1 (pH1N1) viruses genetically related to those in humans. In addition, we isolated H5N2 viruses from two resident species of whistling ducks (genus Dendrocygna) that differed completely from previous South American isolates, instead genetically resembling North American wild bird viruses. Both strains caused low pathogenicity in chickens and mammals. The prevalence and subtype diversity of influenza viruses isolated from diverse species within a small area of Colombia highlights the need for enhanced surveillance throughout South America, including monitoring of the potential transmissibility of low-pathogenic H5N2 viruses from wild birds to domestic poultry and the emergence of reassortant viruses in domestic swine.

Influenza virus subpopulations: exchange of lethal H5N1 virus NS for H1N1 virus NS triggers de novo generation of defective-interfering particles and enhances interferon-inducing particle efficiency

Reassortment of influenza A viruses is known to affect viability, replication efficiency, antigenicity, host range, and virulence, and can generate pandemic strains. In this study, we demonstrated that the specific exchange of the NS gene segment from highly pathogenic A/HK/156/97 (H5N1) [E92 or E92D NS1] virus for the cognate NS gene segment of A/PR/834(H1N1) [D92 NS1] virus did not cause a significant change in the sizes of infectious particle subpopulations. However, it resulted in 2 new phenotypic changes: (1) de novo generation of large subpopulations of defective-interfering particles (DIPs); and (2) enhancement of interferon (IFN)-inducing particle efficiency leading to an order of magnitude or higher quantum (peak) yield of IFN in both avian and mammalian cells. These changes were attributed to loss of function of the H5N1-NS gene products. Most notably, the NS exchange obliterated the usual IFN-induction-suppressing capacity associated with expression of full-size NS1 proteins, and hence functionally mimicked deletions in the NS1 gene. The loss of NS1-mediated suppression of IFN induction, de novo generation of DIPs, and the concomitant enhancement of IFN-inducing particle efficiency suggest that in an attenuated background, the H5N1-NS could be used to formulate a self-adjuvanting live attenuated influenza vaccine similar to viruses with deletions in the NS1 gene.

Effect of natural and chimeric haemagglutinin genes on influenza A virus replication in baby hamster kidney cells

Baby hamster kidney (BHK21) cells are used to produce vaccines against various viral veterinary diseases, including rabies and foot-and-mouth-disease. Although particular influenza virus strains replicate efficiently in BHK21 cells the general use of these cells for influenza vaccine production is prohibited by the poor replication of most strains, including model strain A/PR/8/34 [H1N1] (PR8). We now show that in contrast to PR8, the related strain A/WSN/33 [H1N1] (WSN) replicates efficiently in BHK21 cells. This difference is determined by the haemagglutinin (HA) protein since reciprocal reassortant viruses with swapped HAs behave similarly with respect to growth on BHK21 cells as the parental virus from which their HA gene is derived. The ability or inability of six other influenza virus strains to grow on BHK21 cells appears to be similarly dependent on the nature of the HA gene since reassortant PR8 viruses containing the HA of these strains grow to similar titres as the parental virus from which the HA gene was derived. However, the growth to low titres of a seventh influenza strain was not due to the nature of the HA gene since a reassortant PR8 virus containing this HA grew efficiently on BHK21 cells. Taken together, these results suggest that the HA gene often primarily determines influenza replication efficiency on BHK21 cells but that in some strains other genes are also involved. High virus titres could be obtained with reassortant PR8 strains that contained a chimeric HA consisting of the HA1 domain of PR8 and the HA2 domain of WSN. HA1 contains most antigenic sites and is therefore important for vaccine efficacy. This method of producing the HA1 domain as fusion to a heterologous HA2 domain could possibly also be used for the production of HA1 domains of other viruses to enable the use of BHK21 cells as a generic platform for veterinary influenza vaccine production.

Impact of chicken-origin cells on adaptation of a low pathogenic influenza virus

Understanding the growth dynamics of influenza viruses is an essential step in virus replication and cell-adaptation. The aim of this study was to elucidate the growth kinetic of a low pathogenic avian influenza H9N2 subtype in chicken embryo fibroblast (CEF) and chicken tracheal epithelial (CTE) cells during consecutive passages. An egg-adapted H9N2 virus was seeded into both cell culture systems. The amount of infectious virus released into the cell culture supernatants at interval times post-infection were titered and plaque assayed. The results as well as cell viability results indicate that the infectivity of the influenza virus was different among these primary cells. The egg-adapted H9N2 virus featured higher infectivity in CTE than in CEF cells. After serial passages and plaque purifications of the virus, a CTE cell-adapted strain was generated which carried amino acid substitutions within the HA stem region. The strain showed faster replication kinetics in cell culture resulting in an increase in virus titer. Overall, the present study provides the impact of cell type, multiplicity of infection, cellular protease roles in virus infectivity and finally molecular characterization during H9N2 virus adaptation procedure.

Replication and adaptive mutations of low pathogenic avian influenza viruses in tracheal organ cultures of different avian species

Transmission of avian influenza viruses (AIV) between different avian species may require genome mutations that allow efficient virus replication in a new species and could increase virulence. To study the role of domestic poultry in the evolution of AIV we compared replication of low pathogenic (LP) AIV of subtypes H9N2, H7N7 and H6N8 in tracheal organ cultures (TOC) and primary embryo fibroblast cultures of chicken, turkey, Pekin duck and homing pigeon. Virus strain-dependent and avian species-related differences between LPAIV were observed in growth kinetics and induction of ciliostasis in TOC. In particular, our data demonstrate high susceptibility to LPAIV of turkey TOC contrasted with low susceptibility of homing pigeon TOC. Serial virus passages in the cells of heterologous host species resulted in adaptive mutations in the AIV genome, especially in the receptor-binding site and protease cleavage site of the hemagglutinin. Our data highlight differences in susceptibility of different birds to AIV viruses and emphasizes potential role of poultry in the emergence of new virus variants.

Susceptibility of different cell lines to Avian and Swine Influenza viruses

Influenza outbreaks are widespread in swine and avian populations. Disease control is jeopardized by the extreme antigenic variability of virus strains. Primary isolation of Influenza virus is performed using embryonated chicken eggs (ECE), but alternatives to ECE are badly needed. Although various cultured cells have been used for propagating Influenza A viruses, few types of cells can efficiently support virus replication. One of the most commonly cell lines used in order to isolate Influenza A virus, is represented by the Madin Darby Canine Kidney (MDCK) cell line, but cells derived from primary swine organs (kidney, testicle, lung and trachea) can also be employed. The aim of this study was the evaluation of NSK, MDCK, UMNSAH/DF1 cell lines suitability, compared to ECE for isolation and propagation of Avian and Swine virus subtypes. The results indicated both NSK and MDCK could provide an appropriate substrate for cultivating either Avian (AIV) or Swine (SIV) Influenza virus strains, especially for high pathogenicity Avian Influenza ones. Furthermore, NSK appeared more susceptible than MDCK cells for primary isolation of AIV. In contrast, UMNSAH/DF1 cell line seemed to be less permissive to support Avian virus growth. Furthermore, no SIV replication was detected except for one subtype. Additionally, the results of this study indicated that not all virus strains seemed to adapt with the same efficiency to the different cell lines. On the contrary, chicken embryos were shown to be the most suitable biological system for AIV isolation.

Genome-wide differential gene expression in immortalized DF-1 chicken embryo fibroblast cell line

BACKGROUND

When compared to primary chicken embryo fibroblast (CEF) cells, the immortal DF-1 CEF line exhibits enhanced growth rates and susceptibility to oxidative stress. Although genes responsible for cell cycle regulation and antioxidant functions have been identified, the genome-wide transcription profile of immortal DF-1 CEF cells has not been previously reported. Global gene expression in primary CEF and DF-1 cells was performed using a 4X44K chicken oligo microarray.

RESULTS

A total of 3876 differentially expressed genes were identified with a 2 fold level cutoff that included 1706 up-regulated and 2170 down-regulated genes in DF-1 cells. Network and functional analyses using Ingenuity Pathways Analysis (IPA, Ingenuity® Systems, http://www.ingenuity.com) revealed that 902 of 3876 differentially expressed genes were classified into a number of functional groups including cellular growth and proliferation, cell cycle, cellular movement, cancer, genetic disorders, and cell death. Also, the top 5 gene networks with intermolecular connections were identified. Bioinformatic analyses suggested that DF-1 cells were characterized by enhanced molecular mechanisms for cell cycle progression and proliferation, suppressing cell death pathways, altered cellular morphogenesis, and accelerated capacity for molecule transport. Key molecules for these functions include E2F1, BRCA1, SRC, CASP3, and the peroxidases.

CONCLUSIONS

The global gene expression profiles provide insight into the cellular mechanisms that regulate the unique characteristics observed in immortal DF-1 CEF cells.