Control Of Avian Influenza Research Articles

Genetic and biological characteristics of avian influenza virus subtype H1N8 in environments related to live poultry markets in China

BackgroundSince 2008, avian influenza surveillance in poultry-related environments has been conducted annually in China. Samples have been collected from environments including live poultry markets, wild bird habitats, slaughterhouses, and poultry farms. Multiple subtypes of avian influenza virus have been identified based on environmental surveillance, and an H1N8 virus was isolated from the drinking water of a live poultry market.MethodsVirus isolation was performed by inoculating influenza A-positive specimens into embryonated chicken eggs. Next-generation sequencing was used for whole-genome sequencing. A solid-phase binding assay was performed to test the virus receptor binding specificity. Trypsin dependence plaque formation assays and intravenous pathogenicity index tests were used to evaluate virus pathogenicity in vitro and in vivo, respectively. Different cell lines were chosen for comparison of virus replication capacity.ResultsAccording to the phylogenetic trees, the whole gene segments of the virus named A/Environment/Fujian/85144/2014(H1N8) were of Eurasian lineage. The HA, NA, PB1, and M genes showed the highest homology with those of H1N8 or H1N2 subtype viruses isolated from local domestic ducks, while the PB2, PA, NP and NS genes showed high similarity with the genes of H7N9 viruses detected in 2017 and 2018 in the same province. This virus presented an avian receptor binding preference. The plaque formation assay showed that it was a trypsin-dependent virus. The intravenous pathogenicity index (IVPI) in chickens was 0.02. The growth kinetics of the A/Environment/Fujian/85144/2014(H1N8) virus in different cell lines were similar to those of a human-origin virus, A/Brisbane/59/2007(H1N1), but lower than those of the control avian-origin and swine-origin viruses.ConclusionsThe H1N8 virus was identified in avian influenza-related environments in China for the first time and may have served as a gene carrier involved in the evolution of the H7N9 virus in poultry. This work further emphasizes the importance of avian influenza virus surveillance, especially in live poultry markets (LPMs). Active surveillance of avian influenza in LPMs is a major pillar supporting avian influenza control and response.

Recombinant baculovirus vaccine expressing hemagglutinin of H7N9 avian influenza virus confers full protection against lethal highly pathogenic H7N9 virus infection in chickens.

The emergent highly pathogenic avian influenza A (H7N9) (HPAI) virus is a major public concern in China. Therefore, it is crucially important to develop an effective vaccine against this virus. In this study, we constructed a baculovirus vaccine expressing the hemagglutinin (HA) of H7N9 strain A/Chicken/Jiaxing/148/2014 (JX148). The recombinant baculovirus (rBac-JX148HA) generated in this study showed good growth in insect cells and good safety, and it stably expressed the HA protein. We compared the immunogenicity and efficacy of the inactivated whole-virus vaccine JX148 and rBac-JX148HA. One chicken in the JX148-treated group died on day 4 post-challenge, and three chickens had typical clinical symptoms (survival rate, 90%; morbidity, 40%). However, no chickens immunized with rBac-JX148HA showed clinical signs during the 14-day observation period. An analysis of viral shedding and viral replication demonstrated that rBac-JX148HA more efficiently inhibited viral shedding and viral replication than the inactivated whole-virus vaccine. Taken together, these results indicate that the inactivated recombinant baculovirus vaccine induces a high hemagglutination inhibition antibody titer, provides complete protection against challenge with the highly pathogenic H7N9 virus, and effectively inhibits viral shedding. Therefore, the candidate vaccine has potential utility in the prevention and control of H7N9 avian influenza and is also appropriate for veterinary vaccines using cell suspension culture technology.

Detection of Infection Sources for Avian Influenza A(H7N9) in Live Poultry Transport Network During the Fifth Wave in China

Numerous studies have demonstrated that exposure to live poultry or live poultry markets is the significant risk factor for human infection with avian influenza A(H7N9). However, the specific live poultry markets that are major infection sources for A(H7N9) human cases have not been explored in detail. In this study, we extract data associated with poultry farms, live poultry markets and farmers' markets from Baidu Map using the JavaScript language and then construct the live poultry transport network. From this, we establish our A(H7N9) transmission model over the network based upon probabilistic discrete-time Markov chain. On the basis of the obtained network and model, we propose spatiotemporal backward detection and forward transmission algorithms to detect the most likely infection sources and to compute the first arrival times of the infection sources. Our simulations use these algorithms to identify the specific locations of the infection sources, the first arrival times of the infection sources and the most likely transmission map of the A(H7N9) virus along the live poultry transport network. The results reveal that, in addition to the hazards posed by the live poultry markets, backyard poultry also contributed to A(H7N9) human infections; this risk source was significant especially in the newly affected provinces, in the fifth wave of infection. In particular, by analyzing the temperature characteristics at a given location when the infection source arrived, we find that the risk of human infection with the influenza A(H7N9) virus was high under 9°C~19°C; moderate under 0°C~9°C or 19°C~25°C; and low for temperatures 25°C. Our results suggest that strengthening the supervision of the live poultry market system and immunizing poultry at both live poultry markets and the backyard poultry operations under the high risk temperature band of 9°C~19°C, will be able to significantly contribute to the control of avian influenza A(H7N9) in the future.

Knowledge and Practices towards Avian Influenza among Poultry Workers in Pokhara

Avian influenza is currently a threat to global health. Prevention and control of Avian influenza depends on the knowledge and preventive practices of the poultry workers as well as general population. This article aims to assess the knowledge and preventive practices related to Avian influenza among poultry workers in Pokhara. Descriptive cross sectional study was conducted among 108 poultry workers in Pokhara using purposive sampling. Data was collected through face to face interview using structured interview schedule. The obtained data was analyzed by using descriptive (frequency, percentage, mean and standard deviation) and inferential statistics (Pearson correlation). The findings revealed that only 11.1 percent of the respondents had good knowledge. Only 26.9 percent gave correct answer about causative agent and three out of four gave correct definition of Avian influenza. Nearly two-third of the respondents had good practice of preventive measures. There was no significant relationship (r= 0.117, p= 0.226) between knowledge and practice score. The study concludes that the knowledge of Avian Influenza among poultry workers was low and the Practice was found relatively better. The groups should be targeted for appropriate intervention based on knowledge.

Single Immunization with Newcastle Disease Virus-Vectored H7N9 Vaccine Confers a Complete Protection Against Challenge with Highly Pathogenic Avian Influenza H7N9 Virus

In the fifth wave of the H7N9 avian influenza epidemic, highly pathogenic avian influenza (HPAI) A (H7N9) viruses have emerged and pose a great challenge to public health and the poultry industry. In addition, there are apparent genetic and antigenic variations between the classical H7N9 avian influenza virus and the newly-emerged H7N9 virus. Therefore, an antigenic-match vaccine is required for the prevention and control of H7N9 avian influenza in poultry in China. In this study, a recombinant Newcastle disease virus (NDV)-vectored vaccine expressing the HA derived from a prevailing HPAI H7N9 virus (GD15) was generated using reverse genetics. The recombinant virus (rAI4HA) showed virus yield and growth capacity in chicken embryos comparable to the parental virus (rAI4). Expression of the HA protein was detected in chicken embryo fibroblasts inoculated with rAI4HA. A chicken immunization study demonstrated that both rAI4HA and rAI4 induced similar anti-NDV hemagglutination inhibition (HI) antibody titers at weeks 2, 3, and 4 after a single immunization. However, rAI4HA-immunized chickens had a low seroconversion rate (20%) and negative HI titers against H7N9. Additionally, rAI4HA elicited high levels of H7N9-specifc IgY antibody as measured by ELISA. More importantly, the recombinant vaccine provided a complete protection against a lethal challenge with HPAI H7N9 virus and significantly inhibited virus shedding after a single immunization. Our results suggest that the recombinant NDV-vectored H7N9 vaccine expressing the antigenic-match HA can confer a complete protection against HPAI H7N9 challenge after a single immunization.

Where backyard poultry raisers seek care for sick poultry: implications for avian influenza prevention in Bangladesh

BackgroundIn Bangladesh, backyard poultry raisers lack awareness of avian influenza and infrequently follow government recommendations for its prevention. Identifying where poultry raisers seek care for their ill poultry might help the government better plan how to disseminate avian influenza prevention and control recommendations.MethodsIn order to identify where backyard poultry raisers seek care for their ill poultry, we conducted in-depth and informal interviews: 70 with backyard poultry raisers and six with local poultry healthcare providers in two villages, and five with government veterinary professionals at the sub-district and union levels in two districts during June–August 2009.ResultsMost (86% [60/70]) raisers sought care for their backyard poultry locally, 14% used home remedies only and none sought care from government veterinary professionals. The local poultry care providers provided advice and medications (n = 6). Four local care providers had shops in the village market where raisers sought healthcare for their poultry and the remaining two visited rural households to provide poultry healthcare services. Five of the six local care providers did not have formal training in veterinary medicine. Local care providers either did not know about avian influenza or considered avian influenza to be a disease common among commercial but not backyard poultry. The government professionals had degrees in veterinary medicine and experience with avian influenza and its prevention. They had their offices at the sub-district or union level and lacked staffing to reach the backyard raisers at the village level.ConclusionsThe local poultry care providers provided front line healthcare to backyard poultry in villages and were a potential source of information for the rural raisers. Integration of these local poultry care providers in the government’s avian influenza control programs is a potentially useful approach to increase poultry raisers’ and local poultry care providers’ awareness about avian influenza.

Effectiveness of Market-Level Biosecurity at Reducing Exposure of Poultry and Humans to Avian Influenza: A Systematic Review and Meta-Analysis.

In this study, we aimed to identify the effect of market-level risk factors on avian influenza (AI) infection in poultry and humans and generate evidence that will inform AI prevention and control programs at live bird markets (LBMs). We performed a systematic literature review in both English and Chinese search engines. We estimated the pooled odds ratios of biosecurity indicators relating to AI infections at market level using a quality effects (QE) meta-analysis model. Biosecurity measures effective at reducing AI market contamination and poultry infection at LBMs include smaller market size, selling single poultry species and separating different species, performing cleaning and disinfection and market closures, ban on overnight storage, and sourcing poultry from local areas. Our meta-analysis indicates that higher risk of exposure to AI infection occurs in workers at retail LBMs, female workers, and those who contact ducks, conduct cleaning, slaughtering, defeathering, or evisceration. The most effective strategies to reduce AI market contamination identified in this study should target larger LBMs that are located at noncentral city areas and sell and slaughter multispecies of live poultry. Live bird market workers directly involved in cleaning and poultry processing tasks should participate in occupational health and safety programs.

Characterization of highly pathogenic avian influenza H5N8 virus from Egyptian domestic waterfowl in 2017

ABSTRACTIn 2016, the highly pathogenic avian influenza (HPAI) H5N8 virus was detected in wild birds for the first time in Egypt. In the present study, we identified the HPAI virus H5N8 of clade 2.3.4.4 from domestic waterfowl in Egypt, suggesting its transmission to the domestic poultry from the migratory birds. Based on partial haemagglutinin gene sequence, this virus has a close genetic relationship with subtype H5N8 viruses circulating in Asia and Europe. Pathologically, H5N8 virus in hybrid duck induced nervous signs accompanied by encephalomalacia, haemorrhages, nonsuppurative encephalitis and nonsuppurative vasculitis. The granular layer of cerebellum showed multifocal areas of hydropic degeneration and the Purkinje cell neurons were necrotized or lost. Additionally, the lung, kidney and spleen were congested, and necrotizing pancreatitis was also observed. The co-circulation of both HPAI H5N1 and H5N8 subtypes with the low pathogenic avian influenza H9N2 subtype complicate the control of avian influenza in Egypt with the possibility of emergence of new reassortant viruses. Therefore, continuous monitoring with implementation of strict control measures is required.Research highlightsHPAI H5N8 virus clade 2.3.4.4 was detected in domestic ducks and geese in Egypt in 2017.Phylogenetically, the virus was closely related to HPAI H5N8 viruses identified in Asia and EuropeNonsuppurative encephalitis was widely observed in HPAI H5N8 virus-infected ducks.Degeneration of the cerebellar granular layer was found in most of the brain tissues examined.

Review analysis and impact of co-circulating H5N1 and H9N2 avian influenza viruses in Bangladesh.

Almost the full range of 16 haemagglutinin (HA) and nine neuraminidase subtypes of avian influenza viruses (AIVs) has been detected either in waterfowl, land-based poultry or in the environment in Bangladesh. AIV infections in Bangladesh affected a wide range of host species of terrestrial poultry. The highly pathogenic avian influenza (AI) H5N1 and low pathogenic AI H9N2 were found to co-circulate and be well entrenched in the poultry population, which has caused serious damage to the poultry industry since 2007. By reviewing the available scientific literature, the overall situation of AIVs in Bangladesh is discussed. All Bangladeshi (BD) H5N1 and H9N2 AIV sequences available at GenBank were downloaded along with other representative sequences to analyse the genetic diversity among the circulating AIVs in Bangladesh and to compare with the global situation. Three different H5N1 clades, 2.2.2, 2.3.2.1 and 2.3.4.2, have been detected in Bangladesh. Only 2.3.2.1a is still present. The BD LP H9N2 viruses mostly belonged to the H9 G1 lineage but segregated into many branches, and some of these shared internal genes with HP viruses of subtypes H7N3 and H5N1. However, these reassortment events might have taken place before introduction to Bangladesh. Currently, H9N2 viruses continue to evolve their HA cleavage, receptor binding and glycosylation sites. Multiple mutations in the HA gene associated with adaptation to mammalian hosts were also observed. Strict biosecurity at farms and gradual phasing out of live-bird markets could be the key measures to better control AIVs, whereas stamping out is not a practicable option in Bangladesh. Vaccination also could be an additional tool, which however, requires careful planning. Continuous monitoring of AIVs through systematic surveillance and genetic characterisation of the viruses remains a hallmark of AI control.

Efficacy and synergy of live-attenuated and inactivated influenza vaccines in young chickens.

Outbreaks of novel highly pathogenic avian influenza viruses have been reported in poultry species in the United States since 2014. These outbreaks have proven the limitations of biosecurity control programs, and new tools are needed to reinforce the current avian influenza control arsenal. Some enzootic countries have implemented inactivated influenza vaccine (IIV) in their control programs, but there are serious concerns that a long-term use of IIV without eradication may result in the selection of novel antigenically divergent strains. A broadly protective vaccine is needed, such as live-attenuated influenza vaccine (LAIV). We showed in our previous studies that pc4-LAIV (a variant that encodes a C-terminally truncated NS1 protein) can provide significant protection against heterologous challenge virus in chickens vaccinated at 2–4 weeks of age through upregulation of innate and adaptive immune responses. The current study was conducted to compare the performances of pc4-LAIV and IIV in young chickens vaccinated at 1 day of age. A single dose of pc4-LAIV was able to induce stronger innate and mucosal IgA responses and protect young immunologically immature chickens better than a single dose of IIV. Most importantly, when 1-day-old chickens were intranasally primed with pc4-LAIV and subcutaneously boosted with IIV three weeks later, they showed a rapid, robust, and highly cross-reactive serum antibody response and a high level of mucosal IgA antibody response. This vaccination regimen warrants further optimization to increase its range of protection.

Challenge for One Health: Co-Circulation of Zoonotic H5N1 and H9N2 Avian Influenza Viruses in Egypt.

Highly pathogenic avian influenza (HPAI) H5N1 viruses are currently endemic in poultry in Egypt. Eradication of the viruses has been unsuccessful due to improper application of vaccine-based control strategies among other preventive measures. The viruses have evolved rapidly with increased bird-to-human transmission efficacy, thus affecting both animal and public health. Subsequent spread of potentially zoonotic low pathogenic avian influenza (LPAI) H9N2 in poultry has also hindered efficient control of avian influenza. The H5N1 viruses acquired enhanced bird-to-human transmissibility by (1) altering amino acids in hemagglutinin (HA) that enable binding affinity to human-type receptors, (2) loss of the glycosylation site and 130 loop in the HA protein and (3) mutation of E627K in the PB2 protein to enhance viral replication in mammalian hosts. The receptor binding site of HA of Egyptian H9N2 viruses has been shown to contain the Q234L substitution along with a H191 mutation, which can increase human-like receptor specificity. Therefore, co-circulation of H5N1 and H9N2 viruses in poultry farming and live bird markets has increased the risk of human exposure, resulting in complication of the epidemiological situation and raising a concern for potential emergence of a new influenza A virus pandemic. For efficient control of infection and transmission, the efficacy of vaccine and vaccination needs to be improved with a comprehensive control strategy, including enhanced biosecurity, education, surveillance, rapid diagnosis and culling of infected poultry.

The Effect of Omega 3 and Vitamin E against Avian Influenza in Broiler Chickens

The present study assessed the individual and combined effect of vitamin E and omega 3 against low pathogenic avian influenza (LPAI) virus in broiler birds. Day-old broiler birds (n=125) were equally divided into five groups (A, B, C, D & E). Group A was non infected negative control. While groups B, C, D and E were infected with low pathogenic avian influenza (H9N2) virus at 28th day (2 HAunits/bird). Group B was given omega 3 at rate of 150mg/kg in feed. Group C was given vitamin E 200 IU/kg. Group D was offered vitamin E and omega 3. Group E was designated as positive control without supplementation. The results revealed significantly increased antibody titer, decreased heterophil lymphocyte ratio, improved feed conversion ratio and least histopathological lesions in birds given vitamin E alone followed by the group given combination of vitamin E and omega 3. These results concluded the positive impact of Vitamin E as compare to omega 3 alone and combined omega 3 with vitamin E against LPAI infection in broiler chickens. These findings can have useful field application in control of avian influenza.

System for the heterologous expression of NS1 protein of H9N2 avian influenza virus in the ciliate Tetrahymena thermophila.

Tetrahymena is commonly used as an alternative eukaryotic system for efficiently expressing heterologous genes. In this study, we inserted the non-structural (NS) 1 gene of avian influenza virus (AIV) into the shuttle vector pD5H8 and transformed conjugating T. thermophila with the recombinant plasmid pD5H8-NS1 by particle bombardment. Positive transformants were selected with paromomycin. We demonstrated that the NS1 protein could be expressed steadily following induction with cadmium in this Tetrahymena system. An enzyme-linked immunosorbent assay detection method was preliminary established using the expressed protein as coating antigens for serodiagnosis. This is the first study in which a Tetrahymena expression system was employed for the expression of the AIV NS1 protein, and it provides a good basis for the development of differential diagnostic kits and vaccines for the prevention and control of avian influenza.

Human exposure to live poultry among residents during the second wave of avian influenza A (H7N9) epidemic in Beijing, 2013-2014

Objective: To investigate human exposure to live poultry (poultry feeding and purchasing) in the residents in Beijing and related factors during the second wave of avian influenza A(H7N9) epidemic during 2013-2014, and provide scientific evidence for avian influenza prevention and control. Methods: A total of 7 366 adults aged ≥18 years were selected through multi-stage stratified sampling in Beijing for a questionnaire survey. Logistic regression model was used to analyze the influence factors of human exposure to live poultry. Results: The live poultry feeding rate and live poultry purchasing rate in residents in Beijing in the past year were 5.3% (95%CI: 4.8%-5.8%) and 6.0% (95%CI: 5.5%-6.5%) respectively. Logistic regression analysis indicated that lower educational level of primary school and below, (OR=1.82, 95%CI: 1.22-2.72); being farmer (OR=2.49, 95%CI:1.89-3.29) or being unemployed (OR=1.65, 95%CI: 1.08-2.52); being non local resident (OR=1.54, 95%CI: 1.10-2.16); living in suburban area (OR=2.36, 95%CI: 1.77-3.16); having one child (OR=1.76, 95%CI: 1.42-2.17) or ≥2 children (OR=2.15, 95%CI: 1.43-3.22) in the family were the risk factors associated with feeding poultry compared with higher educational level of college and above, being employed, being local resident, living in urban area and having no child. And being farmer (OR=1.61, 95%CI: 1.27-2.02); being non local resident (OR=1.76, 95%CI: 1.31-2.35); living in suburban area (OR=2.05, 95%CI: 1.61-2.61); having one child (OR=1.24, 95%CI: 1.02-1.52) or ≥2 children (OR=1.78, 95%CI: 1.21-2.63) were the risk factors for purchasing live poultry. Conclusion: Some residents living in Beijing still have exposure to live poultry, and targeted measures should be taken to reduce the exposure to poultry.

English

Avian influenza (AI) causes significant impact on industrial poultry farming, besides infecting a variety of vertebrates. The detection of antibodies against viral antigens by serological methods is important for the epidemiology, control and prevention of AI because their high simplicity and speed for assaying a large number of samples. Obtaining antigenic preparations used for detection of anti-avian influenza virus (AIV) antibodies usually requires complex and expensive procedures and Escherichia coli system expression may be an alternative. The nucleoprotein (NP) of AIV is an ideal antigen candidate because it is highly conserved across AIV strains, resulting in high cross-reactivity and immunogenicity for avian hosts. The NP gene segment was cloned and expressed from AIV isolate H4N6 in E. coli fused to a small ubiquitin-like modifier (SUMO) polypeptide and a poly-histidine tag, obtaining a soluble recombinant NP (rNP) containing the most important epitopes. After purification, the rNP was used as an antigen to develop an indirect rNP-enzyme-linked immunosorbent assay (ELISA) to effectively detect anti-AIV antibodies in chicken serum samples. This rNP-ELISA had high sensitivity (95%), specificity (97%), accuracy (96.7%) and agreement (k=0.88) in a comparative analysis with a commercial ELISA kit. The results suggest that rNP-ELISA offers a viable alternative to improve immunodiagnosis of AIV infection in chickens. Key words: Escherichia coli system expression, small ubiquitin-like modifier (SUMO)-peptide, immunodiagnosis, poultry.

Antigenic diversity of H5 highly pathogenic avian influenza viruses of clade 2.3.4.4 isolated in Asia.

H5 highly pathogenic avian influenza viruses (HPAIV) have spread in both poultry and wild birds since late 2003. Continued circulation of HPAIV in poultry in several regions of the world has led to antigenic drift. In the present study, we analyzed the antigenic properties of H5 HPAIV isolated in Asia using four neutralizing mAbs recognizing hemagglutinin, which were established using A/chicken/Kumamoto/1-7/2014 (H5N8), belonging to clade 2.3.4.4 and also using polyclonal antibodies. Viruses of clades 1.1, 2.3.2.1, 2.3.4, and 2.3.4.4 had different reactivity patterns to the panel of mAbs, thereby indicating that the antigenicity of the viruses of clade 2.3.4.4 were similar but differed from the other clades. In particular, the antigenicity of the viruses of clade 2.3.4.4 differed from those of the viruses of clades 2.3.4 and 2.3.2.1, which suggests that the recent H5 HPAIV have further evolved antigenically divergent. In addition, reactivity of antiserum suggests that the antigenicity of viruses of clade 2.3.4.4 differed slightly among groups A, B, and C. Vaccines are still used in poultry in endemic countries, so the antigenicity of H5 HPAIV should be monitored continually to facilitate control of avian influenza. The panel of mAbs established in the present study will be useful for detecting antigenic drift in the H5 viruses that emerge from the current strains.

Risk factors for avian influenza virus contamination of live poultry markets in Zhejiang, China during the 2015\u20132016 human influenza season

Live bird markets (LBMs), being a potential source of avian influenza virus, require effective environmental surveillance management. In our study, a total of 2865 environmental samples were collected from 292 LBMs during the 2015–2016 human influenza season from 10 cities in Zhejiang province, China. The samples were tested by real-time quantitative polymerase chain reaction (RT-PCR). Field investigations were carried out to investigate probable risk factors. Of the environmental samples, 1519 (53.0%) were contaminated by A subtype. The highest prevalence of the H9 subtype was 30.2%, and the frequencies of the H5 and H7 subtype were 9.3% and 17.3%, respectively. Hangzhou and Jinhua cities were contaminated more seriously than the others. The prevalence of H5/H7/H9 in drinking water samples was highest, at 50.9%, and chopping board swabs ranked second, at 49.3%. Duration of sales per day, types of live poultry, LBM location and the number of live poultry were the main risk factors for environmental contamination, according to logistic regression analysis. In conclusion, LBMs in Zhejiang were contaminated by avian influenza. Our study has provided clues for avian influenza prevention and control during the human influenza season, especially in areas where LBMs are not closed.

A cross-sectional study to quantify the prevalence of avian influenza viruses in poultry at intervention and non-intervention live bird markets in central Vietnam, 2014.

In Vietnam, live bird markets are found in most populated centres, providing the means by which fresh poultry can be purchased by consumers for immediate consumption. Live bird markets are aggregation points for large numbers of poultry, and therefore, it is common for a range of avian influenza viruses to be mixed within live bird markets as a result of different poultry types and species being brought together from different geographical locations. We conducted a cross-sectional study in seven live bird markets in four districts of Thua Thien Hue Province in August and December, 2014. The aims of this study were to (i) document the prevalence of avian influenza in live bird markets (as measured by virus isolation); and (ii) quantify individual bird-, seller- and market-level characteristics that rendered poultry more likely to be positive for avian influenza virus at the time of sale. A questionnaire soliciting details of knowledge, attitude and avian influenza practices was administered to poultry sellers in study markets. At the same time, swabs and faecal samples were collected from individual poultry and submitted for isolation of avian influenza virus. The final data set comprised samples from 1,629 birds from 83 sellers in the seven live bird markets. A total of 113 birds were positive for virus isolation; a prevalence of 6.9 (95% CI 5.8-8.3) avian influenza virus-positive birds per 100 birds submitted for sale. After adjusting for clustering at the market and individual seller levels, none of the explanatory variables solicited in the questionnaire were significantly associated with avian influenza virus isolation positivity. The proportions of variance at the individual market, seller and individual bird levels were 6%, 48% and 46%, respectively. We conclude that the emphasis of avian influenza control efforts in Vietnam should be at the individual seller level as opposed to the market level.

The role of animal reservoirs in social–environmental landscapes: remarks on the control of avian influenza and preparedness for pandemics

Influenza viruses are well known for their ability to infect and cause disease in a broad range of hosts. Modern advances in reverse genetics have enabled scientists to probe the mutations that allow influenza viruses to perform host switching. Despite this detailed understanding of the molecular modifications that allow host switching and adaptation, there is a gap in knowledge regarding the factors external to the virus and their interactions that act as triggers leading to a pandemic. Studies on the ecology of zoonotic pathogens should be the new paradigm for understanding not only influenza viruses but any other infectious disease that can be a threat to animal and human health. The literature regarding influenza pandemics and influenza virus reservoirs was reviewed to analyse how social and economic changes can influence the appearance of new outbreaks of influenza. In addition, the importance of new research in a dynamic environment driven by the expansion of human territories and animal production systems is highlighted. A new paradigm is proposed for novel research approaches to infectious diseases such as influenza.

Recombinant viral-vectored vaccines for the control of avian influenza in poultry

Vaccination is a commonly used tool for the control of both low pathogenic and highly pathogenic avian influenza (AI) viruses. Traditionally, inactivated adjuvanted vaccines made from a low pathogenic field strain have been used for vaccination, but advances in molecular biology have allowed a number of different viral vectored vaccines, expressing the AI virus hemagglutinin (HA) gene, to be developed and licensed for use for control of AI. This review summarizes the licensed vector vaccines available for use in poultry. As a group, these vaccines can stimulate both a cellular and humoral immune response and, when antigenically well matched to the target AI strain, are effective at preventing clinical disease and reducing virus shedding if vaccinated birds do become infected. The vaccines can often be given to one-day old chicks in the hatchery, which can provide early protection and is a cost effective route of administration of the vaccine. All the licensed vectored vaccines, because they only express the HA gene, can potentially be used to differentiate vaccinated from vaccinated and infected birds, which is often referred to as a DIVA strategy. Although a potentially valuable tool for the surveillance of the virus in countries that vaccinate, the DIVA principle has currently not been applied. Concern remains that maternal antibody or pre-existing immunity to the vector or to the AI HA insert can suppress the immune response to the vaccine. The viral vectored vaccines appear to work well with a prime boost strategy where the vectored vaccine is given first and a different type of vaccine, often a killed adjuvanted vaccine is given two or three weeks later.