Infection dynamics of highly pathogenic avian influenza and virulent avian paramyxovirus type 1 viruses in chickens, turkeys and ducks

Mapping the risk of introduction of highly pathogenic avian influenza to Swedish poultry

Outbreaks of highly pathogenic avian influenza (HPAI) have resulted in severe economic impact for national governments and poultry industries globally and in Sweden in recent years. Veterinary authorities can enforce prevention measures, e.g. mandatory indoor housing of poultry, in HPAI high-risk areas. The aim of this study was to conduct a spatiotemporal mapping of the risk of introduction of highly pathogenic avian influenza virus (HPAIV) to Swedish poultry from wild birds, utilising existing data sources. A raster calculation method was used to assess the spatiotemporal risk of introduction of HPAIV to Swedish poultry. The environmental infectious pressure of HPAIV was first calculated in each 5 km by 5 km cell using four risk factors: density of selected species of wild birds, air temperature, presence of agriculture as land cover and presence of HPAI in wild birds based on data from October 2016-September 2021. The relative importance of each risk factor was weighted based on opinion of experts. The estimated environmental infectious pressure was then multiplied with poultry population density to obtain risk values for risk of introduction of HPAIV to poultry. The results showed a large variation in risk both on national and local level. The counties of Skåne and Östergötland particularly stood out regarding environmental infectious pressure, risk of introduction to poultry and detected outbreaks of HPAI. On the other hand, there were counties, identified as having higher risk of introduction to poultry which never experienced any outbreaks. A possible explanation is the variation in poultry production types present in different areas of Sweden. These results indicate that the national and local variation in risk for HPAIV introduction to poultry in Sweden is high, and this would support more targeted compulsory prevention measures than what has previously been employed in Sweden. With the current and evolving HPAI situation in Europe and on the global level, there is a need for continuous updates to the risk map as the virus evolves and circulates in different wild bird species. The study also identified areas of improvement, in relation to data use and data availability, e.g. improvements to poultry registers, inclusion of citizen reported mortality in wild birds, data from standardised wild bird surveys, wild bird migration data as well as results from ongoing risk-factor studies.

Using an adaptive modeling framework to identify avian influenza spillover risk at the wild-domestic interface

The wild to domestic bird interface is an important nexus for emergence and transmission of highly pathogenic avian influenza (HPAI) viruses. Although the recent incursion of HPAI H5N1 Clade 2.3.4.4b into North America calls for emergency response and planning given the unprecedented scale, readily available data-driven models are lacking. Here, we provide high resolution spatial and temporal transmission risk models for the contiguous United States. Considering virus host ecology, we included weekly species-level wild waterfowl (Anatidae) abundance and endemic low pathogenic avian influenza virus prevalence metrics in combination with number of poultry farms per commodity type and relative biosecurity risks at two spatial scales: 3 km and county-level. Spillover risk varied across the annual cycle of waterfowl migration and some locations exhibited persistent risk throughout the year given higher poultry production. Validation using wild bird introduction events identified by phylogenetic analysis from 2022 to 2023 HPAI poultry outbreaks indicate strong model performance. The modular nature of our approach lends itself to building upon updated datasets under evolving conditions, testing hypothetical scenarios, or customizing results with proprietary data. This research demonstrates an adaptive approach for developing models to inform preparedness and response as novel outbreaks occur, viruses evolve, and additional data become available.

Highly Pathogenic Avian Influenza (HPAI) H5 Clade 2.3.4.4b Virus Infection in Birds and Mammals

Avian influenza viruses (AIVs) are highly contagious respiratory viruses of birds, leading to significant morbidity and mortality globally and causing substantial economic losses to the poultry industry and agriculture. Since their first isolation in 2013-2014, the Asian-origin H5 highly pathogenic avian influenza viruses (HPAI) of clade 2.3.4.4b have undergone unprecedented evolution and reassortment of internal gene segments. In just a few years, it supplanted other AIV clades, and now it is widespread in the wild migratory waterfowl, spreading to Asia, Europe, Africa, and the Americas. Wild waterfowl, the natural reservoir of LPAIVs and generally more resistant to the disease, also manifested high morbidity and mortality with HPAIV clade 2.3.4.4b. This clade also caused overt clinical signs and mass mortality in a variety of avian and mammalian species never reported before, such as raptors, seabirds, sealions, foxes, and others. Most notably, the recent outbreaks in dairy cattle were associated with the emergence of a few critical mutations related to mammalian adaptation, raising concerns about the possibility of jumping species and acquisition of sustained human-to-human transmission. The main clinical signs and anatomopathological findings associated with clade 2.3.4.4b virus infection in birds and non-human mammals are hereby summarized.

Species-specific emergence of H7 highly pathogenic avian influenza virus is driven by intrahost selection differences between chickens and ducks

Highly pathogenic avian influenza viruses (HPAIVs) cause severe hemorrhagic disease in terrestrial poultry and are a threat to the poultry industry, wild life, and human health. HPAIVs arise from low pathogenic avian influenza viruses (LPAIVs), which circulate in wild aquatic birds. HPAIV emergence is thought to occur in poultry and not wild aquatic birds, but the reason for this species-restriction is not known. We hypothesized that, due to species-specific tropism and replication, intrahost HPAIV selection is favored in poultry and disfavored in wild aquatic birds. We tested this hypothesis by co-inoculating chickens, representative of poultry, and ducks, representative of wild aquatic birds, with a mixture of H7N7 HPAIV and LPAIV, mimicking HPAIV emergence in an experimental setting. Virus selection was monitored in swabs and tissues by RT-qPCR and immunostaining of differential N-terminal epitope tags that were added to the hemagglutinin protein. HPAIV was selected in four of six co-inoculated chickens, whereas LPAIV remained the major population in co-inoculated ducks on the long-term, despite detection of infectious HPAIV in tissues at early time points. Collectively, our data support the hypothesis that HPAIVs are more likely to be selected at the intrahost level in poultry than in wild aquatic birds and point towards species-specific differences in HPAIV and LPAIV tropism and replication levels as possible explanations.

Clade 2.3.4.4b H5N1 high pathogenicity avian influenza virus (HPAIV) from the 2021/22 epizootic is highly duck adapted and poorly adapted to chickens

The 2021/2022 epizootic of high pathogenicity avian influenza (HPAIV) remains one of the largest ever in the UK, being caused by a clade 2.3.4.4b H5N1 HPAIV. This epizootic affected more than 145 poultry premises, most likely through independent incursion from infected wild birds, supported by more than 1700 individual detections of H5N1 from wild bird mortalities. Here an H5N1 HPAIV, representative of this epizootic (H5N1-21), was used to investigate its virulence, pathogenesis and transmission in layer chickens and Pekin ducks, two species of epidemiological importance. We inoculated both avian species with decreasing H5N1-21 doses. The virus was highly infectious in ducks, with high infection levels and accompanying shedding of viral RNA, even in ducks inoculated with the lowest dose, reflecting the strong waterfowl adaptation of the clade 2.3.4.4 HPAIVs. Duck-to-duck transmission was very efficient, coupled with high environmental contamination. H5N1-21 was frequently detected in water sources, serving as likely sources of infection for ducks, but inhalable dust and aerosols represented low transmission risks. In contrast, chickens inoculated with the highest dose exhibited lower rates of infection compared to ducks. There was no evidence for experimental H5N1-21 transmission to any naive chickens, in two stocking density scenarios, coupled with minimal and infrequent contamination being detected in the chicken environment. Systemic viral dissemination to multiple organs reflected the pathogenesis and high mortalities in both species. In summary, the H5N1-21 virus is highly infectious and transmissible in anseriformes, yet comparatively poorly adapted to galliformes, supporting strong host preferences for wild waterfowl. Key environmental matrices were also identified as being important in the epidemiological spread of this virus during the continuing epizootic.

Protective efficacy of a bivalent H5 influenza vaccine candidate against both clades 2.3.2.1 and 2.3.4.4 high pathogenic avian influenza viruses in SPF chickens

Worldwide, high pathogenic avian influenza viruses belonging to clades 2.3.4.4 and 2.3.2.1 have been circulating in both poultry and wild birds. Since 2018, Korea has built a national antigen bank to ensure preparedness in an emergency. In this study, we developed a bivalent vaccine candidate containing antigens derived from two reassortant KA435/2.3.2.1d and H35/2.3.4.4b strains for Korean national antigen bank. We evaluated its immunogenicity and protective efficacy in specific pathogen free chickens. The two vaccine strains, rgKA435-H9N2 PB2/2.3.2.1d and rgH35/2.3.4.4b, both of which were generated successfully by reverse genetics, were highly immunogenic (titres of haemagglutination inhibition: 8.3 and 8.4 log₂, respectively) and showed good protective efficacy (100 and 147 50% protective dose, respectively) against lethal challenge with wild-type virus when delivered as a 1:1 mixture. Notably, the vaccine provided complete protection against viral shedding at a full dose (512 HAU) and a 1/10 dose (51.2 HAU), with no clinical signs, after challenge with H35/2.3.4.4b. The bivalent vaccine developed in this study may reduce the cost of vaccine production and could be used as a H5 subtype avian influenza vaccine candidate against two clades simultaneously.

Game Birds Can Act as Intermediaries of Virulent Genotype VII Avian Orthoavulavirus-1 between Wild Birds and Domestic Poultry

Newcastle Disease (ND), caused by virulent forms of Avian orthoavulavirus serotype-1 (AOAV-1) is an economically important avian disease worldwide. The past two incursions of ND into the United Kingdom occurred in game bird populations during 2005 and 2006. The nature of the game bird semi-feral rearing system, which can bring these birds into close contact with both wild birds and commercial or backyard poultry, has been hypothesized to act as a bridge between these two environments. As such, the risk that AOAV-1-infected game birds may pose to the UK poultry industry was investigated. Pheasants, partridges and chickens were experimentally infected with the virulent strain APMV-1/Chicken/Bulgaria/112/13, a genotype VII.2 virus associated with ND outbreaks in Eastern Europe. The study demonstrated that both chickens and pheasants are susceptible to infection with APMV-1/Chicken/Bulgaria/112/13, which results in high mortality and onward transmission. Partridges by contrast are susceptible to infection, but mortality was reduced, as was onward transmission. However, the data indicated that both pheasants and partridges may serve as intermediate hosts of AOAV-1 and may bridge the wild bird-domestic poultry interface enabling transmission into an economically damaging environment where morbidity and mortality may be high.

Comparative pathogenesis of two genotype VI.2 avian paramyxovirus type-1 viruses (APMV-1) in pheasants, partridges and chickens

Newcastle disease (ND) is caused by virulent forms of avian paramyxovirus-1 (APMV-1) and is an economically important disease of poultry world-wide. Pigeon paramyxovirus 1 (PPMV-1), a sub-group of APMV-1 is endemic in Columbiformes and can cause infections of poultry. An outbreak of ND in partridges in Scotland, UK, in 2006 (APMV-1/partridge/UK(Scotland)/7575/06) was identified as a class II, genotype VI.2.1.1.2.1, more commonly associated with PPMV-1. It has been hypothesized that game birds may be a route of transmission into commercial poultry settings due to the semi-feral rearing system, which potentially brings them into contact with both wild-birds and poultry species. Therefore, the pathogenesis and transmission of APMV-1/partridge/UK(Scotland)/7575/06 in game birds and chickens was investigated, and compared to a contemporary PPMV-1 isolate, PPMV-1/pigeon/UK/015874/15. Viral shedding and seroconversion profiles demonstrated that pheasants were susceptible to infection with APMV-1/partridge/UK(Scotland)/7575/06 with limited clinical signs observed although they were able to excrete and transmit virus. In contrast, partridges and pheasants showed limited infection with PPMV-1/pigeon/UK/015874/15, causing mild clinical disease. Chickens, however, were productively infected and were able to transmit virus in the absence of clinical signs. From the data, it can be deduced that whilst game birds may play a role in the transmission and epidemiology of genotype VI.2 APMV-1 viruses, the asymptomatic nature of circulation within these species precludes evaluation of natural infection by clinical surveillance. It therefore remains a possibility that genotype VI.2 APMV-1 infection in game birds has the potential for asymptomatic circulation and remains a potential threat to avian production systems.RESEARCH HIGHLIGHTS Demonstration of infection of game birds with Pigeon paramyxovirus-1 (PPMV-1).There are differing dynamics of infection between different game bird species.Differing dynamics of infection between different PPMV-1 isolates and genotypes in game birds and chickens.

Highly Pathogenic Avian Influenza (HPAI H5Nx, Clade 2.3.4.4.b) in Poultry and Wild Birds in Sweden: Synopsis of the 2020-2021 Season

Highly pathogenic avian influenza (HPAI, Gs/Gd lineage) was introduced to Europe in 2005 and has since caused numerous outbreaks in birds. The 2020-2021 season was the hitherto most devastating when considering bird numbers and duration in Europe. Surveillance data, virologic results and epidemiologic investigations from the 2020-2021 outbreaks in Sweden were analysed. Subtypes H5N8 and H5N5 were detected on 24 farms with poultry or other captive birds. In wild birds, subtypes H5N8, H5N5, H5N1, H5N4, H5Nx were detected in 130 out of 811 sampled birds. There was a spatiotemporal association between cases in wild birds and poultry. Based on phylogeny and epidemiology, most of the introductions of HPAI to commercial poultry were likely a result of indirect contact with wild birds. A definite route of introduction to poultry could not be established although some biosecurity breaches were observed. No spread between farms was identified but airborne spread between flocks on the same farm was suspected. Our findings exemplify the challenges posed by the continuously changing influenza viruses that seem to adapt to a broader species spectrum. This points to the importance of wild bird surveillance, compliance to biosecurity, and identification of risk factors for introduction on poultry farms.

Contribution of mutation I142M in fusion protein and Q44R in matrix protein of Newcastle disease virus to virulence in ducks

Although verogenic Newcastle disease viruses (NDVs) generally cause subclinical infection in waterfowls such as ducks, NDVs with high virulence in waterfowl have been sporadically reported. We previously reported that the NDV d5a20b strain, which is obtained by serial passaging of the velogenic 9a5b strain in domestic ducks, showed increased virulence in ducks (Hidaka et al., 2021). The d5a20b strain had 11 amino acid substitutions in its P/V, M, F, HN, and L proteins as compared to 9a5b. In the present study, we generated a series of recombinant (r) NDVs with these amino acid substitutions to identify the molecular basis of virulence of NDV in ducks, and evaluated their influences on virulence and in vitro viral properties. Each of the single amino acid substitutions in either the F protein I142M or the M protein Q44R contributed to the enhancement of intracerebral and intranasal pathogenicity in domestic ducks. The cell-cell fusion activity of the virus with F I142M was five times higher than that of the parental r9a5b. The virus with M Q44R rapidly replicated in duck embryo fibroblasts. Additionally, the rM+F+HN strain, which has the same amino acid sequences as d5a20b in M, F, and HN proteins, showed the highest level of virulence and replication efficiency among the generated recombinant viruses, nearly comparable to rd5a20b. These results suggest that multiple factors are involved in the high growth ability of NDV in duck cells, leading to increased virulence in vivo.

A Semiquantitative Scoring System for Histopathological and Immunohistochemical Assessment of Lesions and Tissue Tropism in Avian Influenza

The main findings of the post-mortem examination of poultry infected with highly pathogenic avian influenza viruses (HPAIV) include necrotizing inflammation and viral antigen in multiple organs. The lesion profile displays marked variability, depending on viral subtype, strain, and host species. Therefore, in this study, a semiquantitative scoring system was developed to compare histopathological findings across a wide range of study conditions. Briefly, the severity of necrotizing lesions in brain, heart, lung, liver, kidney, pancreas, and/or lymphocytic depletion in the spleen is scored on an ordinal four-step scale (0 = unchanged, 1 = mild, 2 = moderate, 3 = severe), and the distribution of the viral antigen in parenchymal and endothelial cells is evaluated on a four-step scale (0 = none, 1 = focal, 2 = multifocal, 3 = diffuse). These scores are used for a meta-analysis of experimental infections with H7N7 and H5N8 (clade 2.3.4.4b) HPAIV in chickens, turkeys, and ducks. The meta-analysis highlights the rather unique endotheliotropism of these HPAIV in chickens and a more severe necrotizing encephalitis in H7N7-HPAIV-infected turkeys. In conclusion, the proposed scoring system can be used to condensate HPAIV-typical pathohistological findings into semiquantitative data, thus enabling systematic phenotyping of virus strains and their tissue tropism.

The Impact of Selected Risk Factors on The Occurrence of Highly Pathogenic Avian Influenza in Commercial Poultry Flocks in Poland

Introduction

Introduction of highly pathogenic avian influenza virus (HPAIV) into a country and its further spread may have a devastating impact on the poultry industry and lead to serious economic consequences. Various risk factors may increase the probability of HPAI outbreak occurrence but their relative influence is often difficult to determine. The study evaluates how the densities of selected poultry species and proximity to the areas inhabited by wild birds impacted HPAI outbreak occurrence during the recently reported epidemics in Poland.

Material and methods

The analysis was developed using these risk factors in the locations of affected and randomly chosen unaffected commercial farms. Generalised linear and non-linear models, specifically logistic regression, classification tree and random forest, were used to indicate the most relevant risk factors, to quantify their association with HPAI outbreak occurrence, and to develop a map depicting spatial risk distribution.

Results

The most important risk factors comprised the densities of turkeys, geese and ducks. The abundance of these species of poultry in an area increased the probability of HPAI occurrence, and their farming intensity in several areas of central, western, eastern and northern Poland put these areas at the highest risk.

Conclusion

The results may improve the targeting of active surveillance, strengthen biosecurity in the areas at risk and contribute to early detection of HPAI in outbreak reoccurrences.

Experimental infection of domestic geese (Anser anser var. domesticus) with H5N8 Gs/GD and H7N1 highly pathogenic avian influenza viruses

Prior to the emergence of the Asian-origin H5 Goose/Guangdong/1/96 (Gs/GD) lineage, highly pathogenic avian influenza viruses (HPAIV) had rarely caused high mortalities in domestic geese. In 2016/2017 European epidemics, H5N8 Gs/GD clade 2.3.4.4 Group B produced an unprecedented number of outbreaks in waterfowl holdings. In this study, the pathogenesis of H5N8 HPAIV in comparison with H7N1 HPAIV, and the role of domestic geese in the epidemiology of these viruses, were evaluated. Local and commercial geese (Anser anser var. domesticus) were intranasally inoculated with 10⁵ ELD₅₀ of A/goose/Spain/IA17CR02699/2017 (H5N8) or A/Chicken/Italy/5093/1999 (H7N1) and monitored daily during 15 days. H5N8 was highly virulent to domestic geese, reaching 100% mortality by 10 days post-infection. Systemic microscopic necrotizing lesions associated with widespread AIV-antigen were detected by IHC techniques, the central nervous system being the most severely affected. High viral loads, measured by qRT-PCR, were present in all samples collected: oral and cloacal swabs, plasma tissues, and moderate levels in pool water. Domestic geese were also susceptible to H7N1 infection, as demonstrated by seroconversion and detection of viral RNA in tissues and plasma in some geese, but all lacked clinical signs. Viral shedding was confirmed in only some geese and was restricted to the oral route, but levels were high and still detected at the end of the study. Overall, H7N1 presents a lower lethality and shedding than H5N8 in geese; however, the viral shedding indicates that these species could play a role in the epidemiology of Gs/GD and other lineages of HPAIVs. RESEARCH HIGHLIGHTS H5N8 Gs/GD clade 2.3.4.4 Group B is highly virulent to domestic geese. The severity of H5N8 is associated with multisystemic replication. H7N1 can infect domestic geese but is avirulent to this species. Domestic geese could play a role in the epidemiology of Gs/GD HPAIVs.

Risk assessment for recrudescence of avian influenza in caged layer houses following depopulation: the effect of cleansing, disinfection and dismantling of equipment

Following an outbreak of highly pathogenic avian influenza virus (HPAIV) in a poultry house, control measures are put in place to prevent further spread. An essential part of the control measures based on the European Commission Avian Influenza Directive 2005/94/EC is the cleansing and disinfection (C&D) of infected premises. Cleansing and disinfection includes both preliminary and secondary C&D, and the dismantling of complex equipment during secondary C&D is also required, which is costly to the owner and also delays the secondary cleansing process, hence increasing the risk for onward spread. In this study, a quantitative risk assessment is presented to assess the risk of re-infection (recrudescence) occurring in an enriched colony-caged layer poultry house on restocking with chickens after different C&D scenarios. The risk is expressed as the number of restocked poultry houses expected before recrudescence occurs. Three C&D scenarios were considered, namely (i) preliminary C&D alone, (ii) preliminary C&D plus secondary C&D without dismantling and (iii) preliminary C&D plus secondary C&D with dismantling. The source-pathway-receptor framework was used to construct the model, and parameterisation was based on the three C&D scenarios. Two key operational variables in the model are (i) the time between depopulation of infected birds and restocking with new birds (TbDR) and (ii) the proportion of infected material that bypasses C&D, enabling virus to survive the process. Probability distributions were used to describe these two parameters for which there was recognised variability between premises in TbDR or uncertainty due to lack of information in the fraction of bypass. The risk assessment estimates that the median (95% credible intervals) number of repopulated poultry houses before recrudescence are 1.2 × 104 (50 to 2.8 × 106), 1.9 × 105 (780 to 5.7 × 107) and 1.1 × 106 (4.2 × 103 to 2.9 × 108) under C&D scenarios (i), (ii) and (iii), respectively. Thus for HPAIV in caged layers, undertaking secondary C&D without dismantling reduces the risk by 16-fold compared to preliminary C&D alone. Dismantling has an additional, although smaller, impact, reducing the risk by a further 6-fold and thus around 90-fold compared to preliminary C&D alone. On the basis of the 95% credible intervals, the model demonstrates the importance of secondary C&D (with or without dismantling) over preliminary C&D alone. However, the extra protection afforded by dismantling may not be cost beneficial in the context of reduced risk of onward spread.

Transmission dynamics between infected waterfowl and terrestrial poultry: Differences between the transmission and tropism of H5N8 highly pathogenic avian influenza virus (clade 2.3.4.4a) among ducks, chickens and turkeys

H5N8 highly-pathogenic avian influenza viruses (HPAIVs, clade 2.3.4.4) have spread globally via migratory waterfowl. Pekin ducks infected with a UK virus (H5N8-2014) served as the donors of infection in three separate cohousing experiments to attempt onward transmission chains to sequentially introduced groups of contact ducks, chickens and turkeys. Efficient transmission occurred among ducks and turkeys up to the third contact stage, with all (100%) birds becoming infected. Introduction of an additional fourth contact group of ducks to the turkey transmission chain demonstrated retention of H5N8-2014's waterfowl-competent adaptation. However, onward transmission ceased in chickens at the second contact stage where only 13% became infected. Analysis of viral progeny at this contact stage revealed no emergent polymorphisms in the intra-species (duck) transmission chain, but both terrestrial species included changes in the polymerase and accessory genes. Typical HPAIV pathogenesis and mortality occurred in infected chickens and turkeys, contrasting with 5% mortality among ducks.

A qualitative risk assessment of cleansing and disinfection requirements after an avian influenza outbreak in commercial poultry

1. During an avian influenza (AI) outbreak in the United Kingdom, the joint aim of the poultry industry and the Government is to eliminate and prevent the spread of infection, through control measures based on the current European Union (EU) Council Directive (2005/94/EC). An essential part of these measures is the cleansing and disinfection (C&D) of infected premises.2. This risk assessment assessed the differences in re-infection in a repopulated flock if the EU Directive is interpreted to permit secondary C&D to be undertaken either with or without dismantling complex equipment. The assessment estimated the probability of virus survival on different types of equipment in a depopulated contaminated poultry house before and after preliminary and secondary C&D procedures. A risk matrix spreadsheet tool was used to carry out the assessment and concluded that, provided secondary C&D is carried out with due diligence (i.e. carried out to a defined code of practice as agreed by both industry and policymakers), the risk of re-infection from equipment is negligible, both with and without dismantling complex equipment in all farm types considered.3. By considering the equipment types individually, the assessment identified those areas of the house which may still contain viable virus post-preliminary C&D and on which attention should be focussed during secondary C&D. The generic risk pathway and matrix spreadsheet tool have the potential to be used for other pathogens and species, given appropriate data.

Comparative clinico-pathological assessment of velogenic (sub-genotype VIIi) and mesogenic (sub-genotype VIm) Avian avulavirus 1 in chickens and pigeons

Newcastle disease (ND), caused by virulent Avian avulavirus 1 (AAvV 1), affects a wide range of avian species worldwide. Recently, several AAvVs of diverse genotypes have emerged with varying genomic and residue substitutions, and subsequent clinical impact on susceptible avian species. We assessed the clinico-pathological influence of two different AAvV 1 pathotypes [wild bird originated-velogenic strain (sub-genotype VIIi, MF437287) and feral pigeon originated-mesogenic strain (sub-genotype VIm, KU885949)] in commercial broiler chickens and pigeons. The velogenic strain caused 100% mortality in both avian species while the mesogenic strain caused 0% and 30% mortality in chickens and pigeons, respectively. Both strains showed tissue tropism for multiple tissues including visceral organs; however, minor variances were observed according to host and pathotype. The observed gross and microscopic lesions were typical of AAvV 1 infection. Utilizing oropharyngeal and cloacal swabs, a comparable pattern of viral shedding was observed for both strains from each of the infected individuals of both avian species. The study concludes a varying susceptibility of chickens and pigeons to different wild bird-originated AAvV 1 pathotypes and, therefore, suggests continuous monitoring and surveillance of currently prevailing strains for effective control of the disease worldwide, particularly in disease-endemic countries.

Virulence of three European highly pathogenic H7N1 and H7N7 avian influenza viruses in Pekin and Muscovy ducks

Background

There is paucity of data on the virulence of highly pathogenic (HP) avian influenza viruses (AIV) H7 in ducks compared to HPAIV H5. Here, the virulence of HPAIV H7N1 (designated H7N1-FPV34 and H7N1-It99) and H7N7 (designated H7N7-FPV27) was assessed in Pekin and/or Muscovy ducklings after intrachoanal (IC) or intramuscular (IM) infection.

Results

The morbidity rate ranged from 60 to 100% and mortality rate from 20 to 80% depending on the duck species, virus strain and/or challenge route. All Muscovy ducklings inoculated IC with H7N7-FPV27 or H7N1-FPV34 exhibited mild to severe clinical signs resulting in the death of 2/10 and 8/10 ducklings, respectively. Also, 2/10 and 6/9 of inoculated Muscovy ducklings died after IC or IM infection with H7N1-It99, respectively. Moreover, 5/10 Pekin ducklings inoculated IC or IM with H7N1-It99 died. The level of virus detected in the oropharyngeal swabs was higher than in the cloacal swabs.

Conclusion

Taken together, HPAIV H7 cause mortality and morbidity in Muscovy and Pekin ducklings. The severity of disease in Muscovy ducklings depended on the virus strain and/or route of infection. Preferential replication of the virus in the respiratory tract compared to the gut merits further investigation.

Wildlife diseases in New Zealand: recent findings and future challenges

Our knowledge of diseases in New Zealand wildlife has expanded rapidly in the last two decades. Much of this is due to a greater awareness of disease as a cause of mortality in some of our highly threatened species or as a limiting factor to the successful captive rearing of intensely managed species such as hihi (Notiomystis cincta), kiwi (Apteryx spp.) and kakapo (Strigops habroptilus). An important factor contributing to the increase of our knowledge has been the development of new diagnostic techniques in the fields of molecular biology and immunohistochemistry, particularly for the diagnosis and epidemiology of viral and protozoan diseases. Although New Zealand remains free of serious exotic viruses there has been much work on understanding the taxonomy and epidemiology of local strains of avipox virus and circoviruses. Bacterial diseases such as salmonellosis, erysipelas and tuberculosis have also been closely investigated in wildlife and opportunist mycotic infections such as aspergillosis remain a major problem in many species. Nutritional diseases such as hyperplastic goitre due to iodine deficiency and metabolic bone disease due to Ca:P imbalance have made significant impacts on some captive reared birds, while lead poisoning is a problem in some localities. The increasing use of wildlife translocations to avoid the extinction of threatened species has highlighted the need for improved methods to assess the disease risks inherent in these operations and other intensive conservation management strategies such as creching young animals. We have also become more aware of the likelihood of inbreeding suppression as populations of many species decrease or pass through a genetic bottleneck. Climate change and habitat loss, however, remain the greatest threats to biodiversity and wildlife health worldwide. Temperature changes will affect our wildlife habitats, alter the distribution of disease vectors and wildlife predators, or directly harm threatened species in vulnerable localities.

Spatial transmission of H5N2 highly pathogenic avian influenza between Minnesota poultry premises during the 2015 outbreak

The spatial spread of highly pathogenic avian influenza (HPAI) H5N2 during the 2015 outbreak in the U.S. state of Minnesota was analyzed through the estimation of a spatial transmission kernel, which quantifies the infection hazard an infectious premises poses to an uninfected premises some given distance away. Parameters were estimated using a maximum likelihood method for the entire outbreak as well as for two phases defined by the daily number of newly detected HPAI-positive premises. The results indicate both a strong dependence of the likelihood of transmission on distance and a significant distance-independent component of outbreak spread for the overall outbreak. The results further suggest that HPAI spread differed during the later phase of the outbreak. The estimated spatial transmission kernel was used to compare the Minnesota outbreak with previous HPAI outbreaks in the Netherlands and Italy to contextualize the Minnesota transmission kernel results and make additional inferences about HPAI transmission during the Minnesota outbreak. Lastly, the spatial transmission kernel was used to identify high risk areas for HPAI spread in Minnesota. Risk maps were also used to evaluate the potential impact of an early marketing strategy implemented by poultry producers in a county in Minnesota during the outbreak, with results providing evidence that the strategy was successful in reducing the potential for HPAI spread.

Immunity Elicited by a Turkey Herpesvirus-Vectored Newcastle Disease Vaccine in Turkey Against Challenge With a Recent Genotype IV Newcastle Disease Virus Field Strain

Newcastle disease (ND) is still a major poultry disease worldwide. Vaccination remains the principal method of controlling ND in endemic countries. Various vaccination strategies, including the use of recently developed recombinant vaccines, have been used to control it. Recombinant vaccines that use the herpesvirus of turkey (HVT) as a vector to express one of the key antigens of Newcastle disease virus (NDV) have been developed to overcome some of the drawbacks related to the use of conventional vaccines. HVT as a vector appears to have unique beneficial characteristics: it is extremely safe, it is not affected by the presence of maternally derived antibodies, and therefore can be applied in the hatchery either in ovo or to day-old chicks. Due to its persistence in the bird, the HVT vector can be expected to induce life-long immune stimulation. In the present study, the efficacy of an HVT-based vector vaccine expressing the F gene of NDV (rHVT-F) was tested against a velogenic genotype IV NDV challenge in commercial turkeys with high levels of maternal antibodies (8.7 ± 0.8 log₂ hemagglutination inhibition titer). The birds were vaccinated on the day of hatch by the subcutaneous route. Development of a humoral immune response to vaccination was detectable from 4 weeks of age by ELISA. The challenge strain used represents recent NDV genotype IV field strains from Morocco. Challenge with this strain induced ND-specific clinical signs and stunting without subsequent mortality in the non-vaccinated birds, whereas the vaccinated turkey poults showed protection as early as 3 weeks of age based on lack of clinical signs, better body weight gain, and reduction of challenge virus shedding. This is the first reported efficacy study of an HVT-vectored ND vaccine against a velogenic NDV challenge in commercial turkeys.

A rapid and transient innate immune response to avian influenza infection in mallards

The vertebrate innate immune system provides hosts with a rapid, non-specific response to a wide range of invading pathogens. However, the speed and duration of innate responses will be influenced by the co-evolutionary dynamics of specific host-pathogen combinations. Here, we show that low pathogenic avian influenza virus (LPAI) subtype H1N1 elicits a strong but extremely transient innate immune response in its main wildlife reservoir, the mallard (Anas platyrhynchos). Using a series of experimental and methodological improvements over previous studies, we followed the expression of retinoic acid inducible gene 1 (RIG-I) and myxovirus resistance gene (Mx) in mallards semi-naturally infected with low pathogenic H1N1. One day post infection, both RIG-I and Mx were significantly upregulated in all investigated tissues. By two days post infection, the expression of both genes had generally returned to basal levels, and remained so for the remainder of the experiment. This is despite the fact that birds continued to actively shed viral particles throughout the study period. We additionally show that the spleen plays a particularly active role in the innate immune response to LPAI. Waterfowl and avian influenza viruses have a long co-evolutionary history, suggesting that the mallard innate immune response has evolved to provide a minimum effective response to LPAIs such that the viral infection is brought under control while minimising the damaging effects of a sustained immune response.

Inferring epidemiologic dynamics from viral evolution: 2014-2015 Eurasian/North American highly pathogenic avian influenza viruses exceed transmission threshold, R0 = 1, in wild birds and poultry in North America

Highly pathogenic avian influenza virus (HPAIV) is a multihost pathogen with lineages that pose health risks for domestic birds, wild birds, and humans. One mechanism of intercontinental HPAIV spread is through wild bird reservoirs, and wild birds were the likely sources of a Eurasian (EA) lineage HPAIV into North America in 2014. The introduction resulted in several reassortment events with North American (NA) lineage low‐pathogenic avian influenza viruses and the reassortant EA/NA H5N2 went on to cause one of the largest HPAIV poultry outbreaks in North America. We evaluated three hypotheses about novel HPAIV introduced into wild and domestic bird hosts: (i) transmission of novel HPAIVs in wild birds was restricted by mechanisms associated with highly pathogenic phenotypes; (ii) the HPAIV poultry outbreak was not self‐sustaining and required viral input from wild birds; and (iii) reassortment of the EA H5N8 generated reassortant EA/NA AIVs with a fitness advantage over fully Eurasian lineages in North American wild birds. We used a time‐rooted phylodynamic model that explicitly incorporated viral population dynamics with evolutionary dynamics to estimate the basic reproductive number (R₀) and viral migration among host types in domestic and wild birds, as well as between the EA H5N8 and EA/NA H5N2 in wild birds. We did not find evidence to support hypothesis (i) or (ii) as our estimates of the transmission parameters suggested that the HPAIV outbreak met or exceeded the threshold for persistence in wild birds (R₀ > 1) and poultry (R₀ ≈ 1) with minimal estimated transmission among host types. There was also no evidence to support hypothesis (iii) because R₀ values were similar among EA H5N8 and EA/NA H5N2 in wild birds. Our results suggest that this novel HPAIV and reassortments did not encounter any transmission barriers sufficient to prevent persistence when introduced to wild or domestic birds.

Infectious dose-dependent accumulation of live highly pathogenic avian influenza H5N1 virus in chicken skeletal muscle-implications for public health

Highly pathogenic avian influenza viruses (HPAIV) of H5N1 subtype are a major global threat to poultry and public health. Export of poultry products, such as chicken and duck meat, is a known source for the cross-boundary spread of HPAI H5N1 viruses. Humans get infected with HPAI H5N1 viruses either by close contact with infected poultry or through consumption of fresh/undercooked poultry meat. Skeletal muscle is the largest soft tissue in chicken that has been shown to contain virus during systemic HPAIV infection and supports productive virus infection. However, the time between infection of a chicken with H5N1 virus and presence of virus in muscle tissue is not yet known. Further, it is also not clear whether chicken infected with low doses of H5N1 virus that cause non-fatal subclinical infections continue to accumulate virus in skeletal muscle. We investigated the amount and duration of virus detection in skeletal muscle of chicken experimentally infected with different doses (10² , 10³ and 10⁴ EID₅₀ ) of a HPAI H5N1 virus. Influenza viral antigen could be detected as early as 6 hr after infection and live virus was recovered from 48 hr after infection. Notably, chicken infected with lower levels of HPAI H5N1 virus (i.e., 10² EID₅₀ ) did not die acutely, but continued to accumulate high levels of H5N1 virus in skeletal muscle until 6 days post-infection. Our data suggest that there is a potential risk of human exposure to H5N1 virus through meat from clinically healthy chicken infected with a low dose of virus. Our results highlight the need to implement rigorous monitoring systems to screen poultry meat from H5N1 endemic countries to limit the global spread of H5N1 viruses.

A Simulation-Based Evaluation of Premovement Active Surveillance Protocol Options for the Managed Movement of Turkeys to Slaughter During an Outbreak of Highly Pathogenic Avian Influenza in the United States

Risk management decisions associated with live poultry movement during a highly pathogenic avian influenza (HPAI) outbreak should be carefully considered. Live turkey movements may pose a risk for disease spread. On the other hand, interruptions in scheduled movements can disrupt business continuity. The Secure Turkey Supply (STS) Plan was developed through an industry-government-academic collaboration to address business continuity concerns that might arise during a HPAI outbreak. STS stakeholders proposed outbreak response measure options that were evaluated through risk assessment. The developed approach relies on 1) diagnostic testing of two pooled samples of swabs taken from dead turkeys immediately before movement via the influenza A matrix gene real-time reverse transcriptase polymerase chain reaction (rRT-PCR) test; 2) enhanced biosecurity measures in combination with a premovement isolation period (PMIP), restricting movement onto the premises for a few days before movement to slaughter; and 3) incorporation of a distance factor from known infected flocks such that exposure via local area spread is unlikely. Daily exposure likelihood estimates from spatial kernels from past HPAI outbreaks were coupled with simulation models of disease spread and active surveillance to evaluate active surveillance protocol options that differ with respect to the number of swabs per pooled sample and the timing of the tests in relation to movement. Simulation model results indicate that active surveillance testing, in combination with strict biosecurity, substantially increased HPAI virus detection probability. When distance from a known infected flock was considered, the overall combined likelihood of moving an infected, undetected turkey flock to slaughter was predicted to be lower at 3 and 5 km. The analysis of different active surveillance protocol options is designed to incorporate flexibility into HPAI emergency response plans.

Pathogenicity and Transmission of H5 and H7 Highly Pathogenic Avian Influenza Viruses in Mallards

Wild aquatic birds have been associated with the intercontinental spread of H5 subtype highly pathogenic avian influenza (HPAI) viruses of the A/goose/Guangdong/1/96 (Gs/GD) lineage during 2005, 2010, and 2014, but dispersion by wild waterfowl has not been implicated with spread of other HPAI viruses. To better understand why Gs/GD H5 HPAI viruses infect and transmit more efficiently in waterfowl than other HPAI viruses, groups of mallard ducks were challenged with one of 14 different H5 and H7 HPAI viruses, including a Gs/GD lineage H5N1 (clade 2.2) virus from Mongolia, part of the 2005 dispersion, and the H5N8 and H5N2 index HPAI viruses (clade 2.3.4.4) from the United States, part of the 2014 dispersion. All virus-inoculated ducks and contact exposed ducks became infected and shed moderate to high titers of the viruses, with the exception that mallards were resistant to Ck/Pennsylvania/83 and Ck/Queretaro/95 H5N2 HPAI virus infection. Clinical signs were only observed in ducks challenged with the H5N1 2005 virus, which all died, and with the H5N8 and H5N2 2014 viruses, which had decreased weight gain and fever. These three viruses were also shed in higher titers by the ducks, which could facilitate virus transmission and spread. This study highlights the possible role of wild waterfowl in the spread of HPAI viruses.

IMPORTANCE

The spread of H5 subtype highly pathogenic avian influenza (HPAI) viruses of the Gs/GD lineage by migratory waterfowl is a serious concern for animal and public health. H5 and H7 HPAI viruses are considered to be adapted to gallinaceous species (chickens, turkeys, quail, etc.) and less likely to infect and transmit in wild ducks. In order to understand why this is different with certain Gs/GD lineage H5 HPAI viruses, we compared the pathogenicity and transmission of several H5 and H7 HPAI viruses from previous poultry outbreaks to Gs/GD lineage H5 viruses, including H5N1 (clade 2.2), H5N8 and H5N2 (clade 2.3.4.4) viruses, in mallards as a representative wild duck species. Surprisingly, most HPAI viruses examined in this study replicated well and transmitted among mallards; however, the three Gs/GD lineage H5 HPAI viruses replicated to higher titers, which could explain the transmission of these viruses in susceptible wild duck populations.

Quantitative Estimation of the Number of Contaminated Hatching Eggs Released from an Infected, Undetected Turkey Breeder Hen Flock During a Highly Pathogenic Avian Influenza Outbreak

The regulatory response to an outbreak of highly pathogenic avian influenza (HPAI) in the United States may involve quarantine and stop movement orders that have the potential to disrupt continuity of operations in the U.S. turkey industry--particularly in the event that an uninfected breeder flock is located within an HPAI Control Area. A group of government-academic-industry leaders developed an approach to minimize the unintended consequences associated with outbreak response, which incorporates HPAI control measures to be implemented prior to moving hatching eggs off of the farm. Quantitative simulation models were used to evaluate the movement of potentially contaminated hatching eggs from a breeder henhouse located in an HPAI Control Area, given that active surveillance testing, elevated biosecurity, and a 2-day on-farm holding period were employed. The risk analysis included scenarios of HPAI viruses differing in characteristics as well as scenarios in which infection resulted from artificial insemination. The mean model-predicted number of internally contaminated hatching eggs released per movement from an HPAI-infected turkey breeder henhouse ranged from 0 to 0.008 under the four scenarios evaluated. The results indicate a 95% chance of no internally contaminated eggs being present per movement from an infected house before detection. Sensitivity analysis indicates that these results are robust to variation in key transmission model parameters within the range of their estimates from available literature. Infectious birds at the time of egg collection are a potential pathway of external contamination for eggs stored and then moved off of the farm; the predicted number of such infectious birds was estimated to be low. To date, there has been no evidence of vertical transmission of HPAI virus or low pathogenic avian influenza virus to day-old poults from hatching eggs originating from infected breeders. The application of risk analysis methods was beneficial for evaluating outbreak measures developed through emergency response planning initiatives that consider the managed movement of hatching eggs from monitored premises in an HPAI Control Area.

Experimental co-infections of domestic ducks with a virulent Newcastle disease virus and low or highly pathogenic avian influenza viruses

Infections with avian influenza viruses (AIV) of low and high pathogenicity (LP and HP) and Newcastle disease virus (NDV) are commonly reported in domestic ducks in many parts of the world. However, it is not clear if co-infections with these viruses affect the severity of the diseases they produce, the amount of virus shed, and transmission of the viruses. In this study we infected domestic ducks with a virulent NDV virus (vNDV) and either a LPAIV or a HPAIV by giving the viruses individually, simultaneously, or sequentially two days apart. No clinical signs were observed in ducks infected or co-infected with vNDV and LPAIV, but co-infection decreased the number of ducks shedding vNDV and the amount of virus shed (P<0.01) at 4 days post inoculation (dpi). Co-infection did not affect the number of birds shedding LPAIV, but more LPAIV was shed at 2 dpi (P<0.0001) from ducks inoculated with only LPAIV compared to ducks co-infected with vNDV. Ducks that received the HPAIV with the vNDV simultaneously survived fewer days (P<0.05) compared to the ducks that received the vNDV two days before the HPAIV. Co-infection also reduced transmission of vNDV to naïve contact ducks housed with the inoculated ducks. In conclusion, domestic ducks can become co-infected with vNDV and LPAIV with no effect on clinical signs but with reduction of virus shedding and transmission. These findings indicate that infection with one virus can interfere with replication of another, modifying the pathogenesis and transmission of the viruses.

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.

Immune responses of poultry to Newcastle disease virus

Newcastle disease (ND) remains a constant threat to poultry producers worldwide, in spite of the availability and global employment of ND vaccinations since the 1950s. Strains of Newcastle disease virus (NDV) belong to the order Mononegavirales, family Paramyxoviridae, and genus Avulavirus, are contained in one serotype and are also known as avian paramyxovirus serotype-1 (APMV-1). They are pleomorphic in shape and are single-stranded, non-segmented, negative sense RNA viruses. The virus has been reported to infect most orders of birds and thus has a wide host range. Isolates are characterized by virulence in chickens and the presence of basic amino acids at the fusion protein cleavage site. Low virulent NDV typically produce subclinical disease with some morbidity, whereas virulent isolates can result in rapid, high mortality of birds. Virulent NDV are listed pathogens that require immediate notification to the Office of International Epizootics and outbreaks typically result in trade embargos. Protection against NDV is through the use of vaccines generated with low virulent NDV strains. Immunity is derived from neutralizing antibodies formed against the viral hemagglutinin and fusion glycoproteins, which are responsible for attachment and spread of the virus. However, new techniques and technologies have also allowed for more in depth analysis of the innate and cell-mediated immunity of poultry to NDV. Gene profiling experiments have led to the discovery of novel host genes modulated immediately after infection. Differences in virus virulence alter host gene response patterns have been demonstrated. Furthermore, the timing and contributions of cell-mediated immune responses appear to decrease disease and transmission potential. In view of recent reports of vaccine failure from many countries on the ability of classical NDV vaccines to stop spread of disease, renewed interest in a more complete understanding of the global immune response of poultry to NDV will be critical to developing new control strategies and intervention programs for the future.

High genetic diversity of Newcastle disease virus in poultry in West and Central Africa: cocirculation of genotype XIV and newly defined genotypes XVII and XVIII

Despite rampant Newcastle disease virus (NDV) outbreaks in Africa for decades, the information about the genetic characteristics of the virulent strains circulating in West and Central Africa is still scarce. In this study, 96 complete NDV fusion gene sequences were obtained from poultry sampled in Cameroon, Central African Republic, Côte d'Ivoire, and Nigeria between 2006 and 2011. Based on rational criteria recently proposed for the classification of NDV strains into classes, genotypes, and subgenotypes, we revisited the classification of virulent strains, in particular those from West and Central Africa, leading to their grouping into genotype XIV and newly defined genotypes XVII and XVIII, each with two subgenotypes. Phylogenetic analyses revealed that several (sub)genotypes are found in almost every country. In Cameroon, most strains were related to vaccine strains, but a single genotype XVII strain was also found. Only three highly similar genotype XVII strains were detected in Central African Republic. Subgenotypes XVIIa, XVIIIa, and XVIIIb cocirculated in Côte d'Ivoire, while subgenotypes XIVa, XIVb, XVIIa, XVIIb, and XVIIIb were found in Nigeria. While these genotypes are so far geographically restricted, local and international trade of domestic and exotic birds may lead to their spread beyond West and Central Africa. A high genetic diversity, mutations in important neutralizing epitopes paired with suboptimal vaccination, various levels of clinical responses of poultry and wild birds to virulent strains, strains with new cleavage sites, and other genetic modifications found in these genotypes tend to undermine and complicate NDV management in Africa.

Impact of virus strain characteristics on early detection of highly pathogenic avian influenza infection in commercial table-egg layer flocks and implications for outbreak control

Early detection of highly pathogenic avian influenza (HPAI) infection in commercial poultry flocks is a critical component of outbreak control. Reducing the time to detect HPAI infection can reduce the risk of disease transmission to other flocks. The timeliness of different types of detection triggers could be dependent on clinical signs that are first observed in a flock, signs that might vary due to HPAI virus strain characteristics. We developed a stochastic disease transmission model to evaluate how transmission characteristics of various HPAI strains might effect the relative importance of increased mortality, drop in egg production, or daily real-time reverse transcriptase (RRT)-PCR testing, toward detecting HPAI infection in a commercial table-egg layer flock. On average, daily RRT-PCR testing resulted in the shortest time to detection (from 3.5 to 6.1 days) depending on the HPAI virus strain and was less variable over a range of transmission parameters compared with other triggers evaluated. Our results indicate that a trigger to detect a drop in egg production would be useful for HPAI virus strains with long infectious periods (6-8 days) and including an egg-drop detection trigger in emergency response plans would lead to earlier and consistent reporting in some cases. We discuss implications for outbreak control and risk of HPAI spread attributed to different HPAI strain characteristics where an increase in mortality or a drop in egg production or both would be among the first clinical signs observed in an infected flock.

Progress in control of H5N1 highly pathogenic avian influenza and the future for eradication

Three broad factors, occurring concurrently, prevent elimination of highly pathogenic avian influenza caused by viruses of the H5N1 subtype (H5N1 HPAI) in countries and subregions where infection has remained endemic. These factors are the nature of the poultry sector, the quality of veterinary and animal production services (both public and private) serving the poultry industry, and the extent and level of commitment at all levels to virus elimination. Most of these countries have developed and adopted programs for progressive control of H5N1 HPAI, focused on the local factors hindering elimination of the viruses. Based on the rate of implementation of these measures over the last 5 to 7 yr (during which time there has been unprecedented financial and technical support from the international donor community), it is not expected that global eradication of H5N1 HPAI viruses can be achieved within the next 10 yr. If the "classical" approach to control, based around early case detection and culling, were adopted in a zone containing millions of free-running ducks, the work load required to complete even the first round of testing would exceed existing capacity. There would be no guarantees of sustained success locally, especially if the viruses are not eradicated regionally.

The pathobiology of two Indonesian H5N1 avian influenza viruses representing different clade 2.1 sublineages in chickens and ducks

To determine the pathobiology of Indonesian H5N1 highly pathogenic avian influenza, two viruses representing clades 2.1.1 and 2.1.3 were inoculated into broiler chickens and Pekin ducks via the eyes, nostrils and oropharynx. In chickens, both viruses produced fulminant disease; tissue tropism was broad but predominantly endothelial and viral loads in tissues were high. Except for one case of meningoencephalitis, the infection in ducks was sub-clinical, leading only to seroconversion. In these ducks, virus and viral antigen occurred in lower amounts, mainly in the respiratory tract (airsac and sinuses), prior to day 7 after inoculation. During clinical disease, chickens shed high virus titres orally and cloacally. Ducks intermittently shed low virus titres from the oral route for up to 8 days post-inoculation. We discuss the significance of the data for understanding the pathogenesis and pathobiology of Indonesian H5N1 in chickens and ducks.

Comparative study on the pathogenesis of the generated 9a5b Newcastle disease virus mutant isolate between chickens and waterfowl

Lentogenic Newcastle disease viruses (NDVs), circulating among waterfowl, have the potential to become highly pathogenic by replication in chickens. The pathological studies that compare NDV infections in chickens and waterfowl are rare. The virulent 9a5b mutant NDV isolate was generated by passaging the lentogenic Goose/Alaska/415/91 NDV isolate in chickens. The pathogenesis of the virulent 9a5b mutant isolate is unknown in both chickens and waterfowl. In this study, the virulent 9a5b mutant NDV isolate was inoculated intranasally in 32-day-old specific pathogen-free white Leghorn chickens and Japanese commercial ducks. Unlike ducks, which remained clinically normal throughout the study, chickens had depression, gasping, oral discharges, and greenish-white soft feces. Gross and histologic lesion patterns as well as viral replication supported the differing clinical outcome. Ducks had slight inflammation mainly in respiratory and digestive tracts, whereas slight nonpurulent encephalitis, necrotizing pancreatitis, tubulointerstitial nephritis, and mild inflammation in respiratory and digestive tracts were detected in chickens. In agreement, interferon-beta (IFN-β)-immunopositive signals were more intense in lung tissue of ducks than that of chickens, and NDV replications were detected intensively in chicken tissues. These results suggest that the 9a5b mutant NDV isolate is more virulent in chickens, and slight histological lesions were induced in ducks even with virulent NDVs.

Quantifying transmission of highly pathogenic and low pathogenicity H7N1 avian influenza in turkeys

Outbreaks of avian influenza in poultry can be devastating, yet many of the basic epidemiological parameters have not been accurately characterised. In 1999-2000 in Northern Italy, outbreaks of H7N1 low pathogenicity avian influenza virus (LPAI) were followed by the emergence of H7N1 highly pathogenic avian influenza virus (HPAI). This study investigates the transmission dynamics in turkeys of representative HPAI and LPAI H7N1 virus strains from this outbreak in an experimental setting, allowing direct comparison of the two strains. The fitted transmission rates for the two strains are similar: 2.04 (1.5-2.7) per day for HPAI, 2.01 (1.6-2.5) per day for LPAI. However, the mean infectious period is far shorter for HPAI (1.47 (1.3-1.7) days) than for LPAI (7.65 (7.0-8.3) days), due to the rapid death of infected turkeys. Hence the basic reproductive ratio, [Formula: see text] is significantly lower for HPAI (3.01 (2.2-4.0)) than for LPAI (15.3 (11.8-19.7)). The comparison of transmission rates and [Formula: see text] are critically important in relation to understanding how HPAI might emerge from LPAI. Two competing hypotheses for how transmission rates vary with population size are tested by fitting competing models to experiments with differing numbers of turkeys. A model with frequency-dependent transmission gives a significantly better fit to experimental data than density-dependent transmission. This has important implications for extrapolating experimental results from relatively small numbers of birds to the commercial poultry flock size, and for how control, including vaccination, might scale with flock size.

Sunshine virus in Australian pythons

Sunshine virus is a recently discovered novel paramyxovirus that is associated with illness in snakes. It does not phylogenetically cluster within either of the two currently accepted paramyxoviral subfamilies. It is therefore only distantly related to the only other known genus of reptilian paramyxoviruses, Ferlavirus, which clusters within the Paramyxovirinae subfamily. Clinical and diagnostic aspects associated with Sunshine virus are as yet undescribed. The objective of this paper was to report the clinical presentation, virus isolation, PCR testing and pathology associated with Sunshine virus infection. Clinical records and samples from naturally occurring cases were obtained from two captive snake collections and the archives of a veterinary diagnostic laboratory. The clinical signs that are associated with Sunshine virus infection are localised to the neurorespiratory systems or are non-specific (e.g. lethargy, inappetence). Out of 15 snakes that were infected with Sunshine virus (detected in any organ by either virus isolation or PCR), the virus was isolated from four out of ten (4/10) sampled brains, 3/10 sampled lungs and 2/7 pooled samples of kidney and liver. In these same 15 snakes, PCR was able to successfully detect Sunshine virus in fresh-frozen brain (11/11), kidney (7/8), lung (8/11) and liver (5/8); and various formalin-fixed paraffin-embedded tissues (7/8). During a natural outbreak of Sunshine virus in a collection of 32 snakes, the virus could be detected in five out of 39 combined oral-cloacal swabs that were collected from 23 of these snakes over a 105 day period. All snakes that were infected with Sunshine virus were negative for reovirus and ferlavirus by PCR. Snakes infected with Sunshine virus reliably exhibited hindbrain white matter spongiosis and gliosis with extension to the surrounding grey matter and neuronal necrosis evident in severe cases. Five out of eight infected snakes also exhibited mild bronchointerstitial pneumonia. Infection with Sunshine virus should be considered by veterinarians investigating disease outbreaks in snakes, particularly those that are associated with neurorespiratory disease.

Role of position 627 of PB2 and the multibasic cleavage site of the hemagglutinin in the virulence of H5N1 avian influenza virus in chickens and ducks

Highly pathogenic H5N1 avian influenza viruses have caused major disease outbreaks in domestic and free-living birds with transmission to humans resulting in 59% mortality amongst 564 cases. The mutation of the amino acid at position 627 of the viral polymerase basic-2 protein (PB2) from glutamic acid (E) in avian isolates to lysine (K) in human isolates is frequently found, but it is not known if this change affects the fitness and pathogenicity of the virus in birds. We show here that horizontal transmission of A/Vietnam/1203/2004 H5N1 (VN/1203) virus in chickens and ducks was not affected by the change of K to E at PB2-627. All chickens died between 21 to 48 hours post infection (pi), while 70% of the ducks survived infection. Virus replication was detected in chickens within 12 hours pi and reached peak titers in spleen, lung and brain between 18 to 24 hours for both viruses. Viral antigen in chickens was predominantly in the endothelium, while in ducks it was present in multiple cell types, including neurons, myocardium, skeletal muscle and connective tissues. Virus replicated to a high titer in chicken thrombocytes and caused upregulation of TLR3 and several cell adhesion molecules, which may explain the rapid virus dissemination and location of viral antigen in endothelium. Virus replication in ducks reached peak values between 2 and 4 days pi in spleen, lung and brain tissues and in contrast to infection in chickens, thrombocytes were not involved. In addition, infection of chickens with low pathogenic VN/1203 caused neuropathology, with E at position PB2-627 causing significantly higher infection rates than K, indicating that it enhances virulence in chickens.