Genetic Characterization of Highly Pathogenic Avian Influenza A(H5N8) Virus in Pakistani Live Bird Markets Reveals Rapid Diversification of Clade 2.3.4.4b Viruses.

The highly pathogenic (HPAI) avian influenza A(H5N1) viruses have undergone reassortment with multiple non-N1-subtype neuraminidase genes since 2008, leading to the emergence of H5Nx viruses. H5Nx viruses established themselves quickly in birds and disseminated from China to Africa, the Middle East, Europe and North America. Multiple genetic clades have successively evolved through frequent mutations and reassortment, posing a continuous threat to domestic poultry and causing substantial economic losses. Live bird markets are recognized as major sources of avian-to-human infection and for the emergence of zoonotic influenza. In Pakistan, the A(H5N1) virus was first reported in domestic birds in 2007; however, avian influenza surveillance is limited and there is a lack of knowledge on the evolution and transmission of the A(H5) virus in the country. We collected oropharyngeal swabs from domestic poultry and environmental samples from six different live bird markets during 2018-2019. We detected and sequenced HPAI A(H5N8) viruses from two chickens, one quail and one environmental sample in two markets. Temporal phylogenetics indicated that all novel HPAI A(H5N8) viruses belonged to clade 2.3.4.4b, with all eight genes of Pakistan A(H5N8) viruses most closely related to 2017 Saudi Arabia A(H5N8) viruses, which were likely introduced via cross-border transmission from neighboring regions approximately three months prior to virus detection into domestic poultry. Our data further revealed that clade 2.3.4.4b viruses underwent rapid lineage expansion in 2017 and acquired significant amino acid mutations, including mutations associated with increased haemagglutinin affinity to human α-2,6 receptors, prior to the first human A(H5N8) infection in Russian poultry workers in 2020. These results highlight the need for systematic avian influenza surveillance in live bird markets in Pakistan to monitor for potential A(H5Nx) variants that may arise from poultry populations.

Assessment of A20 infectious laryngotracheitis vaccine take in meat chickens using swab and dust samples following mass vaccination in drinking water.

Infectious laryngotracheitis, caused by the alphaherpesvirus infectious laryngotracheitis virus (ILTV), is an important disease of chickens. Partial control of this disease in meat chickens is commonly achieved by mass vaccination with live virus in drinking water. There is a need for a practical test to evaluate vaccination outcomes. For the Serva ILTV vaccine, quantitative real-time PCR (qPCR) enumeration of ILTV genome copies (GC) in flock level dust samples collected at 7-8 days post vaccination (dpv) can be used to differentiate flocks with poor and better vaccine take. This study aimed to validate this approach for A20, another widely used ILT vaccine in Australia. In four meat chicken flocks vaccinated with A20 in water using two different water stabilization times (20 or 40 min), swabs from the trachea and choanal cleft and dust samples were collected at 0, 7, 14 and 21 dpv. ILTV GC detection in swabs and dust was highest at 7 dpv and at this time ILTV GC load in dust was strongly and positively associated with vaccine take in individual birds assessed by swab samples. Choanal cleft swabs provided significantly fewer ILTV positive results than paired tracheal swab samples but the level of ILTV GC detected was similar. Water stabilization time had only minor effects on vaccination response in favour of the shorter time. Location of dust collection had no effect on viral load measured in dust samples. Dust samples collected at 0 and 7 dpv can be used to assess the vaccination status of flocks.

Biosafety risk assessment for production of candidate vaccine viruses to protect humans from zoonotic highly pathogenic avian influenza viruses.

A major lesson learned from the public health response to the 2009 H1N1 pandemic was the need to shorten the vaccine delivery timeline to achieve the best pandemic mitigation results. A gap analysis of previous pre-pandemic vaccine development activities identified possible changes in the Select Agent exclusion process that would maintain safety and shorten the timeline to develop candidate vaccine viruses (CVVs) for use in pandemic vaccine manufacture. Here, we review the biosafety characteristics of CVVs developed in the past 15 years to support a shortened preparedness timeline for A(H5) and A(H7) subtype highly pathogenic avian influenza (HPAI) CVVs. Extensive biosafety experimental evidence supported recent changes in the implementation of Select Agent regulations that eliminated the mandatory chicken pathotype testing requirements and expedited distribution of CVVs to shorten pre-pandemic and pandemic vaccine manufacturing by up to 3 weeks.

Influenza A viruses in birds and humans: Prevalence, molecular characterization, zoonotic significance and risk factors' assessment in poultry farms.

This study aimed to investigate the prevalence of influenza A viruses in birds and humans residing in the same localities of Sharkia Province, Egypt and the risk factors' assessment in poultry farms. A total of 100 birds comprised of 50 chickens, 25 ducks and 25 wild egrets were sampled. Swab samples were collected from 65 people (50 poultry farm workers and 15 hospitalized patients). All samples were screened for the presence of influenza A viruses using isolation and molecular assays. Avian influenza viruses were only detected in chicken samples (18%) and molecularly confirmed as subtype H5. The infection rate was higher in broilers (40%) than layers (8.6%). Influenza A (H1) pdm09 virus was detected in a single human case (1.54%). All the isolated AI H5 viruses were clustered into clade (2.2.1.2) and shared a high similarity rate at nucleotides and amino acid levels. In addition, they had a multi-basic amino acid motif (ـــPQGEKRRKKR/GLFـــ) at the H5 gene cleavage site that exhibited point mutations. Chicken breed, movement of workers from one flock to another, lack of utensils' disinfection and the introduction of new birds to the farm were significant risk factors associated with highly pathogenic AI H5 virus infection in poultry farms (p ≤ 0.05). Other factors showed no significant association. The HPAI H5 viruses are still endemic in Egypt with continuous mutation. Co-circulation of these viruses in birds and pdm09 viruses in humans raises alarm for the emergence of reassortant viruses that are capable of potentiating pandemics.

Modelling the outbreak of infectious disease following mutation from a non-transmissible strain.

In-host mutation of a cross-species infectious disease to a form that is transmissible between humans has resulted with devastating global pandemics in the past. We use simple mathematical models to describe this process with the aim to better understand the emergence of an epidemic resulting from such a mutation and the extent of measures that are needed to control it. The feared outbreak of a human-human transmissible form of avian influenza leading to a global epidemic is the paradigm for this study. We extend the SIR approach to derive a deterministic and a stochastic formulation to describe the evolution of two classes of susceptible and infected states and a removed state, leading to a system of ordinary differential equations and a stochastic equivalent based on a Markov process. For the deterministic model, the contrasting timescale of the mutation process and disease infectiousness is exploited in two limits using asymptotic analysis in order to determine, in terms of the model parameters, necessary conditions for an epidemic to take place and timescales for the onset of the epidemic, the size and duration of the epidemic and the maximum level of the infected individuals at one time. Furthermore, the basic reproduction number R0 is determined from asymptotic analysis of a distinguished limit. Comparisons between the deterministic and stochastic model demonstrate that stochasticity has little effect on most aspects of an epidemic, but does have significant impact on its onset particularly for smaller populations and lower mutation rates for representatively large populations. The deterministic model is extended to investigate a range of quarantine and vaccination programmes, whereby in the two asymptotic limits analysed, quantitative estimates on the outcomes and effectiveness of these control measures are established.

The live poultry trade and the spread of highly pathogenic avian influenza: Regional differences between Europe, West Africa, and Southeast Asia.

In the past two decades, avian influenzas have posed an increasing international threat to human and livestock health. In particular, highly pathogenic avian influenza H5N1 has spread across Asia, Africa, and Europe, leading to the deaths of millions of poultry and hundreds of people. The two main means of international spread are through migratory birds and the live poultry trade. We focus on the role played by the live poultry trade in the spread of H5N1 across three regions widely infected by the disease, which also correspond to three major trade blocs: the European Union (EU), the Economic Community of West African States (ECOWAS), and the Association of Southeast Asian Nations (ASEAN). Across all three regions, we found per-capita GDP (a proxy for modernization, general biosecurity, and value-at-risk) to be risk reducing. A more specific biosecurity measure-general surveillance-was also found to be mitigating at the all-regions level. However, there were important inter-regional differences. For the EU and ASEAN, intra-bloc live poultry imports were risk reducing while extra-bloc imports were risk increasing; for ECOWAS the reverse was true. This is likely due to the fact that while the EU and ASEAN have long-standing biosecurity standards and stringent enforcement (pursuant to the World Trade Organization's Agreement on the Application of Sanitary and Phytosanitary Measures), ECOWAS suffered from a lack of uniform standards and lax enforcement.

Economic factors influencing zoonotic disease dynamics: demand for poultry meat and seasonal transmission of avian influenza in Vietnam.

While climate is often presented as a key factor influencing the seasonality of diseases, the importance of anthropogenic factors is less commonly evaluated. Using a combination of methods - wavelet analysis, economic analysis, statistical and disease transmission modelling - we aimed to explore the influence of climatic and economic factors on the seasonality of H5N1 Highly Pathogenic Avian Influenza in the domestic poultry population of Vietnam. We found that while climatic variables are associated with seasonal variation in the incidence of avian influenza outbreaks in the North of the country, this is not the case in the Centre and the South. In contrast, temporal patterns of H5N1 incidence are similar across these 3 regions: periods of high H5N1 incidence coincide with Lunar New Year festival, occurring in January-February, in the 3 climatic regions for 5 out of the 8 study years. Yet, daily poultry meat consumption drastically increases during Lunar New Year festival throughout the country. To meet this rise in demand, poultry production and trade are expected to peak around the festival period, promoting viral spread, which we demonstrated using a stochastic disease transmission model. This study illustrates the way in which economic factors may influence the dynamics of livestock pathogens.

Safe application of regionalization for trade in poultry and poultry products during highly pathogenic avian influenza outbreaks in the USA.

The 2014-2015 H5Nx high pathogenicity avian influenza (HPAI) outbreak affected 211 commercial premises, 21 backyard flocks, 75 individual wild birds and four captive-reared raptors in 21 Western and upper Midwestern states, resulting in death or culling of over 50.4 million poultry in the stamping-out programme that cost the US government $850 million. The outbreak had a negative $3.3 billion impact on the economy. Seventeen trading partners suspended imports of all US-origin poultry and poultry products while 38 trading partners regionalized the United States, and allowed trade in poultry and poultry products to continue from areas of the US not affected by HPAI. Disease response and control activities in addition to the use of comprehensive surveillance and regionalization (zoning) as prescribed by the OIE Terrestrial Animal Health Code are a scientifically valid and effective means to maintain safe trade in poultry and poultry products. This was further realized during the 2016 H7N8 HPAI outbreak in Dubois County, Indiana, with greater acceptance of regionalization and continuity in trade with a more limited cost of $30 million for eradication.

Epidemic Reconstruction in a Phylogenetics Framework: Transmission Trees as Partitions of the Node Set.

The use of genetic data to reconstruct the transmission tree of infectious disease epidemics and outbreaks has been the subject of an increasing number of studies, but previous approaches have usually either made assumptions that are not fully compatible with phylogenetic inference, or, where they have based inference on a phylogeny, have employed a procedure that requires this tree to be fixed. At the same time, the coalescent-based models of the pathogen population that are employed in the methods usually used for time-resolved phylogeny reconstruction are a considerable simplification of epidemic process, as they assume that pathogen lineages mix freely. Here, we contribute a new method that is simultaneously a phylogeny reconstruction method for isolates taken from an epidemic, and a procedure for transmission tree reconstruction. We observe that, if one or more samples is taken from each host in an epidemic or outbreak and these are used to build a phylogeny, a transmission tree is equivalent to a partition of the set of nodes of this phylogeny, such that each partition element is a set of nodes that is connected in the full tree and contains all the tips corresponding to samples taken from one and only one host. We then implement a Monte Carlo Markov Chain (MCMC) procedure for simultaneous sampling from the spaces of both trees, utilising a newly-designed set of phylogenetic tree proposals that also respect node partitions. We calculate the posterior probability of these partitioned trees based on a model that acknowledges the population structure of an epidemic by employing an individual-based disease transmission model and a coalescent process taking place within each host. We demonstrate our method, first using simulated data, and then with sequences taken from the H7N7 avian influenza outbreak that occurred in the Netherlands in 2003. We show that it is superior to established coalescent methods for reconstructing the topology and node heights of the phylogeny and performs well for transmission tree reconstruction when the phylogeny is well-resolved by the genetic data, but caution that this will often not be the case in practice and that existing genetic and epidemiological data should be used to configure such analyses whenever possible. This method is available for use by the research community as part of BEAST, one of the most widely-used packages for reconstruction of dated phylogenies.

Control of highly pathogenic avian influenza in Quang Tri province, Vietnam: voices from the human-animal interface.

INTRODUCTION: Highly pathogenic avian influenza (HPAI) is caused by the haemagglutinin 5, neuraminidase 1 (H5N1) influenza A virus. Around 80% of households in rural Vietnam raise poultry, which provides food security and nutrition to their households and beyond. Of these, around 15-20% are semi-commercial producers, producing at least 28% of the country's chicken. Through learning the experiences of these semi-commercial farmers, this study aimed to explore the local understandings and sociocultural aspects of HPAI's impact, particularly the aetiology, diagnosis, and the prevention and control methods in one Vietnamese rural province. METHODS: This study was conducted in Quang Tri province, Vietnam. Quang Tri province has eight districts. Five of these districts were at high risk of HPAI during the study period, of which three were selected for the present study. Within these three districts, six communes were randomly selected for the study from the list of intervention communes in Quang Tri province. Six out of the 26 intervention communes in Quang Tri were therefore selected. Participants were randomly selected and recruited from lists of semi-commercial farmers, village animal health workers, village human health workers and local authorities so that the study population (representative population) included an amount of variability similar to that of the wider population. RESULTS: A key benefit of this village-level control program was the residential proximity of animal and human health professionals. Participants were well aware of the typical clinical signs for avian influenza and of the reporting process for suspect cases. However there was extensive room for improvement in Quang Tri province regarding access to the HPAI vaccine, essential medical equipment for animal use, and available financial support. CONCLUSIONS: This qualitative research study provided an important insight for in-country policy makers and international stakeholders. It is vital that there are continued efforts to prevent and control highly pathogenic avian influenza through support programs that provide locally appropriate information and resources to those at the human-animal interface.

Evaluating the risk of avian influenza introduction and spread among poultry exhibition flocks in Australia.

Some practices undertaken by poultry exhibitors, such as allowing wild birds to contact domestic birds, the high frequency of bird movements and the lack of appropriate isolation for incoming birds, pose a risk for disease introduction and spread. The aim of the current study was to quantitatively assess the probability of introduction of low pathogenic avian influenza (LPAI) viruses from wild waterfowl into poultry exhibition flocks and the subsequent spread to other poultry flocks. Exposure and consequence assessments, using scenario trees and Monte Carlo stochastic simulation modelling, were conducted to identify potential pathways of introduction and spread and calculate the probabilities of these pathways occurring. Input parameters were estimated from two recently conducted cross-sectional studies among poultry exhibitors in Australia (Dusan et al., 2010; Hernández-Jover et al., 2013) and other scientific literature. According to reported practices of poultry exhibitors and the LPAI prevalence in wild birds in Australia, this assessment estimates a median (5-95%) probability of exposure of a bird kept by a poultry exhibitor of 0.004 (0.003-0.005). Due to the higher susceptibility of infection of turkeys and waterfowl, this probability is higher in flocks keeping these bird species than in those keeping chickens or pigeons only. Similarly, once exposure has occurred, establishment of infection and subsequent spread are more likely in those flocks keeping waterfowl and turkeys than in those keeping chicken and pigeons only. Spread through movement of birds is the most likely pathway of spread, followed by contaminated fomites, wild birds and airborne spread. The median probability of LPAI spread through movement of birds in flocks keeping waterfowl and turkeys was estimated to be 0.280 (0.123-0.541) and 0.230 (0.104-0.421), respectively. A lower probability was estimated for chicken (0.087; 0.027-0.202) and pigeon (0.0003; 3.0×10(-5)-0.0008) flocks. The sensitivity analysis indicates that the prevalence of LPAI in wild waterfowl and the probability of contact of domestic birds with wild waterfowl are the most influential parameters on the probability of exposure; while the probability of spread is mostly influenced by the probability of movement of birds and the probability of the exhibitor detecting and reporting LPAI. To minimize the potential risk of AI introduction and spread, poultry exhibitors should prevent contact of domestic birds with wild birds, and implement appropriate biosecurity practices. In addition, adequate extension services are required to improve exhibitors' abilities to recognize diseases and reporting behaviour.

'One health' and development priorities in resource-constrained countries: policy lessons from avian and pandemic influenza preparedness in Zambia.

'One World, One Health' has become a key rallying theme for the integration of public health and animal health priorities, particularly in the governance of pandemic-scale zoonotic infectious disease threats. However, the policy challenges of integrating public health and animal health priorities in the context of trade and development issues remain relatively unexamined, and few studies to date have explored the implications of global disease governance for resource-constrained countries outside the main centres of zoonotic outbreaks. This article draws on a policy study of national level avian and pandemic influenza preparedness between 2005 and 2009 across the sectors of trade, health and agriculture in Zambia. We highlight the challenges of integrating disease control interventions amidst trade and developmental realities in resource-poor environments. One Health prioritizes disease risk mitigation, sidelining those trade and development narratives which speak to broader public health concerns. We show how locally important trade and development imperatives were marginalized in Zambia, limiting the effectiveness of pandemic preparedness. Our findings are likely to be generalizable to other resource-constrained countries, and suggest that effective disease governance requires alignment with trade and development sectors, as well as integration of veterinary and public health sectors.

Viral lung infections: epidemiology, virology, clinical features, and management of avian influenza A(H7N9).

PURPOSE OF REVIEW: The avian influenza A(H7N9) virus has jumped species barrier and caused severe human infections. Here, we present the virological features relevant to clinical practice, and summarize the epidemiology, clinical findings, diagnosis, treatment, and preventive strategies of A(H7N9) infection. RECENT FINDINGS: As of 18 February 2014, A(H7N9) virus has caused 354 infections in mainland China, Taiwan, and Hong Kong with a case-fatality rate of 32%. Elderly men were most affected. Most patients acquired the infection from direct contact with poultry or from a contaminated environment, although person-to-person transmission has likely occurred. A(H7N9) infection has usually presented with severe pneumonia, often complicated by acute respiratory distress syndrome and multiorgan failure. Mild infections have been reported in children and young adults. Nasopharyngeal aspirate and sputum samples should be collected for diagnosis, preferably using reverse transcriptase-PCR. Early treatment with neuraminidase inhibitors improved survival, but the efficacy of antivirals was hampered by resistant mutants. The closure of live poultry markets in affected areas has significantly contributed to the decline in the incidence of human cases. SUMMARY: The emergence of A(H7N9) virus represents a significant health threat. High vigilance is necessary so that appropriate treatment can be instituted for the patient and preventive measures can be implemented.

Hazard analysis of critical control points assessment as a tool to respond to emerging infectious disease outbreaks.

Highly pathogenic avian influenza virus (HPAI) strain H5N1 has had direct and indirect economic impacts arising from direct mortality and control programmes in over 50 countries reporting poultry outbreaks. HPAI H5N1 is now reported as the most widespread and expensive zoonotic disease recorded and continues to pose a global health threat. The aim of this research was to assess the potential of utilising Hazard Analysis of Critical Control Points (HACCP) assessments in providing a framework for a rapid response to emerging infectious disease outbreaks. This novel approach applies a scientific process, widely used in food production systems, to assess risks related to a specific emerging health threat within a known zoonotic disease hotspot. We conducted a HACCP assessment for HPAI viruses within Vietnam's domestic poultry trade and relate our findings to the existing literature. Our HACCP assessment identified poultry flock isolation, transportation, slaughter, preparation and consumption as critical control points for Vietnam's domestic poultry trade. Introduction of the preventative measures highlighted through this HACCP evaluation would reduce the risks posed by HPAI viruses and pressure on the national economy. We conclude that this HACCP assessment provides compelling evidence for the future potential that HACCP analyses could play in initiating a rapid response to emerging infectious diseases.

Risk factors and characteristics of low pathogenic avian influenza virus isolated from commercial poultry in Tunisia.

OBJECTIVE: Estimate the seroprevalence of influenza A virus in various commercial poultry farms and evaluate specific risk factors as well as analyze their genetic nature using molecular assays. MATERIALS AND METHODS: This report summarizes the findings of a national survey realized from October 2010 to May 2011 on 800 flocks in 20 governorates. Serum samples were screened for the presence of specific influenza virus antibodies using cELISA test. Additionally, swab samples were tested by real time and conventional RT-PCR and compared with results obtained by others assays. Phylogenetic and genetic analyses of the glycoproteins were established for some strains. RESULTS: Out of the 800 chicken and turkey flocks tested by cELISA, 223 showed positive anti-NP antibodies (28.7%, 95% CI: 25.6-32.1). Significantly higher seroprevalence was found among the coastal areas compared to inland and during the autumn and winter. Broiler flocks showed significantly lower seroprevalence than layers and broiler breeders. The influenza virus infection prevalence increased after the laying phase among layer flocks. In addition, AIV seropositivity was significantly associated with low biosecurity measures. The Ag EIA and rRT-PCR tests revealed significantly higher numbers of AI positive samples as compared to cell cultures or egg inoculation. All new strains were subtyped as H9N2 by real time and conventional RT-PCR. Drift mutations, addition or deletion of glycosylation sites were likely to have occurred in the HA and NA glycoproteins of Tunisian strains resulting in multiple new amino acid substitutions. This fact may reflect different evolutionary pressures affecting these glycoproteins. The role of these newly detected substitutions should be tested. CONCLUSION: Our findings highlight the potential risk of AIV to avian health. Strict enforcement of biosecurity measures and possible vaccination of all poultry flocks with continuous monitoring of poultry stations may ensure reduction of AIV prevalence and avoid emergence of more pathogenic strains.

A one health perspective on HPAI H5N1 in the Greater Mekong sub-region.

Highly pathogenic avian influenza H5N1 has been a global concern for almost 10 years since its epidemic emergence in South-east Asia in 2003/2004. Despite large investment of resources into the region, the infection has not been eradicated and continues to result in outbreaks in poultry and a small number of human fatalities. This review synthesizes the knowledge base generated by a vast number of research activities conducted in the region and beyond, and adopts an interdisciplinary perspective consistent with the one health paradigm towards analysing the problem and formulating possible policy solutions. A key outcome of the work has been the need to integrate socio-economic and anthropological dimensions with any disease control and prevention activities traditionally informed by primarily epidemiological, virological and pathological attributes of the infection in poultry and wild waterbirds. Recommendations at a broad conceptual level are presented that acknowledge the diversity in the region with respect to livestock production, as well as the changing nature of the risk landscape as a consequence of the rapid economic development which some of the countries in the Greater Mekong sub-region are currently undergoing, as well as their strong trade links with China as the major economic power in East Asia.

Occupational exposure assessment using antibody levels: exposure to avian leukosis/sarcoma viruses in the poultry industry.

Avian leukosis/sarcoma viruses (ALSV) infect and cause cancers in chickens. Poultry workers are exposed to ALSV and other infectious agents in the workplace. This study examines if industrial hygiene assessment of antibody levels in poultry workers can identify risky job tasks at the higher exposure risk to an infectious agent, i.e., ALSV. We compared ALSV antibody levels in poultry workers and control subjects. Occupational and demographical factors were examined for an association with the exposure risk in poultry workers. We found that the antibody levels were significantly higher in poultry workers than in control subjects. Job category and age together were significantly associated with the antibody levels in workers. Certain job tasks were identified with significantly higher antibody levels as compared to others, implying that recommendations should be made to protect workers at these jobs. The findings of this study indicate that the measurement of antibody levels in workers can be useful for industrial hygiene assessment of exposure to infectious agents.

Industrial hygiene assessment of reticuloendotheliosis viruses exposure in the poultry industry.

OBJECTIVES: Reticuloendotheliosis viruses (REV) are a group of retroviruses like avian leukosis/sarcoma viruses (ALSV) that naturally infect and cause cancers in chickens. We recently found that ALSV antibody levels were associated with job tasks in the poultry industry. The objectives of this study are to examine whether a similar association can be found with REV antibody levels and to examine the correlation between REV and ALSV antibody levels. METHODS: Relative risk was estimated comparing REV antibody levels of 45 poultry workers with those of 44 controls. The expected mean antibody level was predicted for the association with employment by a generalized linear model. Correlation coefficient was measured between ALSV and REV antibody levels. RESULTS: REV antibody levels were significantly higher in poultry workers than in control subjects and were associated with gender and employment conditions, especially employment duration. The relative risk was significantly higher for some job categories. A significant correlation was observed between REV and ALSV antibody levels, which was strong among poultry workers, but weak among the control subjects. CONCLUSION: Antibody levels can be validly used to identify certain job tasks associated with high risk of exposure to REV in the workplace, and the practical implication is recommendations for protection at these job tasks. Importantly, in situations where there is exposure to multiple pathogens in the workplace, the analysis of antibody levels of one pathogen may sufficiently represent exposure to the other correlated pathogens. This suggested exposure assessment may hold true for pathogens with a similar route of transmission.

Impact of the implementation of rest days in live bird markets on the dynamics of H5N1 highly pathogenic avian influenza.

Live bird markets (LBMs) act as a network 'hub' and potential reservoir of infection for domestic poultry. They may therefore be responsible for sustaining H5N1 highly pathogenic avian influenza (HPAI) virus circulation within the poultry sector, and thus a suitable target for implementing control strategies. We developed a stochastic transmission model to understand how market functioning impacts on the transmission dynamics. We then investigated the potential for rest days-periods during which markets are emptied and disinfected-to modulate the dynamics of H5N1 HPAI within the poultry sector using a stochastic meta-population model. Our results suggest that under plausible parameter scenarios, HPAI H5N1 could be sustained silently within LBMs with the time spent by poultry in markets and the frequency of introduction of new susceptible birds' dominant factors determining sustained silent spread. Compared with interventions applied in farms (i.e. stamping out, vaccination), our model shows that frequent rest days are an effective means to reduce HPAI transmission. Furthermore, our model predicts that full market closure would be only slightly more effective than rest days to reduce transmission. Strategies applied within markets could thus help to control transmission of the disease.

Assessment of farm-level biosecurity measures after an outbreak of avian influenza in the United Kingdom.

During Avian Influenza outbreaks in England, the 'AI Order' states that a poultry keeper may be required to keep domestic birds separate from wild birds. This study aimed to assess a) how effectively this was done and b) the negative impact this had for bird owners and animal welfare during the November 2007 Highly Pathogenic Avian Influenza (HPAI) outbreak in Suffolk, UK. A voluntary questionnaire was posted to holdings (n=296) that were within 10 km of an infected premises; these holdings were required to separate domestic and wild birds where possible. Holdings were identified during outbreak investigations conducted by the authorities. Holdings of all sizes were included. A sample of holdings received a follow-up visit or telephone call to validate the questionnaire (n=29). From the 38% of eligible holdings that responded, 13% (95% CI 7-22%) left their birds outdoors throughout the outbreak. If game birds were excluded, 9% (CI 4-17%) of holdings did not house their birds. Major cost and welfare problems were rare; however, there were exceptions. Enforced housing was often relaxed before a minor welfare problem deteriorated. Contact between wild and domestic birds was greatly reduced during the outbreak, resulting in a reduced probability of HPAI transmission via wild birds for most, but not all, holdings.