Performance of gross lesions at postmortem for the detection of outbreaks during the avian influenza A virus (H7N7) epidemic in The Netherlands in 2003

Highly pathogenic avian influenza subtype H5Nx clade 2.3.4.4 outbreaks in Dutch poultry farms, 2014-2018: Clinical signs and mortality

In recent years, different subtypes of highly pathogenic avian influenza (HPAI) viruses caused outbreaks in several poultry types worldwide. Early detection of HPAI virus infection is crucial to reduce virus spread. Previously, the use of a mortality ratio threshold to expedite notification of suspicion in layer farms was proposed. The purpose of this study was to describe the clinical signs reported in the early stages of HPAI H5N8 and H5N6 outbreaks on chicken and Pekin duck farms between 2014 and 2018 in the Netherlands and compare them with the onset of an increased mortality ratio (MR). Data on daily mortality and clinical signs from nine egg-producing chicken farms and seven Pekin duck farms infected with HPAI H5N8 (2014 and 2016) and H5N6 (2017-2018) in the Netherlands were analysed. In 12 out of 15 outbreaks for which a MR was available, MR increase preceded or coincided with the first observation of clinical signs by the farmer. In one chicken and two Pekin duck outbreaks, clinical signs were observed prior to MR increase. On all farms, veterinarians observed clinical signs of general disease. Nervous or locomotor signs were reported in all Pekin duck outbreaks, but only in two chicken outbreaks. Other clinical signs were observed less frequently in both chickens and Pekin ducks. Compared to veterinarians, farmers observed and reported clinical signs, especially respiratory and gastrointestinal signs, less frequently. This case series suggests that a MR with a set threshold could be an objective parameter to detect HPAI infection on chicken and Pekin duck farms at an early stage. Observation of clinical signs may provide additional indication for farmers and veterinarians for notifying a clinical suspicion of HPAI infection. Further assessment and validation of a MR threshold in Pekin ducks are important as it could serve as an important tool in HPAI surveillance programs.

Emergence and multiple reassortments of French 2015-2016 highly pathogenic H5 avian influenza viruses

From November 2015 to August 2016, 81 outbreaks of highly pathogenic (HP) H5 avian influenza virus were detected in poultry farms from South-Western France. These viruses were mainly detected in farms raising waterfowl, but also in chicken or guinea fowl flocks, and did not induce severe signs in waterfowl although they did meet the HP criteria. Three different types of neuraminidases (N1, N2 and N9) were associated with the HP H5 gene. Full genomes sequences of 24 H5HP and 6 LP viruses that circulated in the same period were obtained by next generation sequencing, from direct field samples or after virus isolation in SPF embryonated eggs. Phylogenetic analyses of the eight viral segments confirmed that they were all related to the avian Eurasian lineage. In addition, analyses of the "Time of the Most Recent Common Ancestor" showed that the common ancestor of the H5HP sequences from South-Western France could date back to early 2014 (±1 year). This pre-dated the first detection of H5 HP in poultry farms and was consistent with a silent circulation of these viruses for several months. Finally, the phylogenetic study of the different segments showed that several phylogenetic groups could be established. Twelve genotypes of H5HP were detected implying that at least eleven reassortment events did occur after the H5HP cleavage site emerged. This indicates that a large number of co-infections with both highly pathogenic H5 and other avian influenza viruses must have occurred, a finding that lends further support to prolonged silent circulation.

Low-pathogenic notifiable avian influenza serosurveillance and the risk of infection in poultry - a critical review of the European Union active surveillance programme (2005-2007)

Please cite this paper as: Gonzales et al. (2010) Low‐pathogenic notifiable avian influenza serosurveillance and the risk of infection in poultry – a critical review of the European Union active surveillance programme (2005–2007). Influenza and Other Respiratory Viruses 4(2), 91–99.

Background  Since 2003, Member States (MS) of the European Union (EU) have implemented serosurveillance programmes for low pathogenic notifiable avian influenza (LPNAI) in poultry. To date, there is the need to evaluate the surveillance activity in order to optimize the programme’s surveillance design.

Objectives  To evaluate MS sampling operations [sample size and targeted poultry types (PTs)] and its relation with the probability of detection and to estimate the PTs relative risk (RR) of being infected.

Methods  Reported data of the surveillance carried out from 2005 to 2007 were analyzed using: (i) descriptive indicators to characterize both MS sampling operations and its relation with the probability of detection and the LPNAI epidemiological situation, and (ii) multivariable methods to estimate each PTs RR of being infected.

Results  Member States sampling a higher sample size than that recommended by the EU had a significantly higher probability of detection. Poultry types with ducks & geese, game‐birds, ratites and “others” had a significant higher RR of being seropositive than chicken categories. The seroprevalence in duck & geese and game‐bird holdings appears to be higher than 5%, which is the EU‐recommended design prevalence (DP), while in chicken and turkey categories the seroprevalence was considerably lower than 5% and with that there is the risk of missing LPNAI seropositive holdings.

Conclusion  It is recommended that the European Commission discusses with its MS whether the results of our evaluation calls for refinement of the surveillance characteristics such as sampling frequency, the between‐holding DP and MS sampling operation strategies.

Pathology and virus distribution in chickens naturally infected with highly pathogenic avian influenza A virus (H7N7) During the 2003 outbreak in The Netherlands

The largest recorded outbreak of highly pathogenic avian influenza virus of the subtype H7N7 occurred in The Netherlands in 2003. We describe the immunohistochemical and histopathologic findings of 3 chickens naturally infected during this outbreak. Influenza virus antigen occurred in endothelial cells and mononuclear cells of all tissues examined and occurred in parenchymal cells of heart, lung, kidney, pancreas, and trachea, often associated with multifocal inflammation and necrosis. These findings are consistent with the acute stage of highly pathogenic avian influenza from other subtypes. In the severely edematous wattle skin, most endothelial cells contained virus antigen, while in all other tissues virus antigen was only detected in a few endothelial cells. Virus histochemistry showed that this H7N7 virus attached to more endothelial cells in wattle skin than in other vascular beds. This might explain, at least partly, the tropism of the virus and the associated severity of lesions in this tissue.

Detection of mortality clusters associated with highly pathogenic avian influenza in poultry: a theoretical analysis

Rapid detection of infectious disease outbreaks is often crucial for their effective control. One example is highly pathogenic avian influenza (HPAI) such as H5N1 in commercial poultry flocks. There are no quantitative data, however, on how quickly the effects of HPAI infection in poultry flocks can be detected. Here, we study, using an individual-based mathematical model, time to detection in chicken flocks. Detection is triggered when mortality, food or water intake or egg production in layers pass recommended thresholds suggested from the experience of past HPAI outbreaks. We suggest a new threshold for caged flocks--the cage mortality detection threshold--as a more sensitive threshold than current ones. Time to detection is shown to depend nonlinearly on R0 and is particularly sensitive for R0<10. It also depends logarithmically on flock size and number of birds per cage. We also examine how many false alarms occur in uninfected flocks when we vary detection thresholds owing to background mortality. The false alarm rate is shown to be sensitive to detection thresholds, dependent on flock size and background mortality and independent of the length of the production cycle. We suggest that current detection thresholds appear sufficient to rapidly detect the effects of a high R0 HPAI strain such as H7N7 over a wide range of flock sizes. Time to detection of the effects of a low R0 HPAI strain such as H5N1 can be significantly improved, particularly for large flocks, by lowering detection thresholds, and this can be accomplished without causing excessive false alarms in uninfected flocks. The results are discussed in terms of optimizing the design of disease surveillance programmes in general.

The onset of virus shedding and clinical signs in chickens infected with high-pathogenicity and low-pathogenicity avian influenza viruses

Some avian influenza viruses may be transmissible to mammals by ingestion. Cats and dogs have been infected by H5N1 avian influenza viruses when they ate raw poultry, and two human H5N1 infections were linked to the ingestion of uncooked duck blood. The possibility of zoonotic influenza from exposure to raw poultry products raises concerns about flocks with unrecognized infections. The present review examines the onset of virus shedding and the development of clinical signs for a variety of avian influenza viruses in chickens. In experimentally infected birds, some high-pathogenicity avian influenza (HPAI) and low-pathogenicity avian influenza (LPAI) viruses can occur in faeces and respiratory secretions as early as 1 to 2 days after inoculation. Some HPAI viruses have also been found in meat 1 day after inoculation and in eggs after 3 days. There is no evidence that LPAI viruses can be found in meat, and the risk of their occurrence in eggs is poorly understood. Studies in experimentally infected birds suggest that clinical signs usually develop within a few days of virus shedding; however, some models and outbreak descriptions suggest that clinical signs may not become evident for a week or more in some H5 or H7 HPAI-infected flocks. During this time, avian influenza viruses might be found in poultry products. LPAI viruses can be shed in asymptomatically infected or minimally affected flocks, but these viruses are unlikely to cause significant human disease.

Avian influenza outbreak management: action at time of confirmation, depopulation and disposal methods; the 'Belgian experience' during the H7N7 highly pathogenic avian influenza epidemic in 2003

Eradication of H5 and H7 influenza in a positive flock will include mass depopulation of birds, containment and inactivation of the virus in the carcasses and litter, and decontamination of the facility. A quick response is desired in the event of a disease outbreak. Ideally, birds should be depopulated within 24 h after detecting the virus. Mass depopulation of birds must be performed in a humane manner while minimizing human health and biosecurity risks. In the framework of the European legislation, a number of methods are authorized for the killing of poultry for processing prior to marketing. However, during emergencies such as a disease outbreak, there are fewer options. The current most commonly used procedures for large-scale emergency depopulation of birds consist of exposing poultry to CO or CO(2) gas. Both gasses have been used in Belgium during the H7N7 crisis in 2003. The gassing procedures include whole house gassing, portable panel enclosures, cage cabinets, containers and polyethylene tent method. Whole house gassing requires sealing the house to prevent gas leakage and, using specialized equipment, introducing large volumes of gas evenly over the birds. All procedures are very labour intensive, create a biosecurity risk and require a large number of personnel. There are considerable region-to-region differences in emergency depopulation techniques and disposal of carcasses and infected material. Because of the differences in bird type and species, management, housing and stocking density, it is difficult to propose a depopulation technique that will be suitable for all circumstances. Safety of the human operators is an increasing concern with all H5 and H7 strains and in particular with the highly pathogenic H5N1 strain. Researchers and commercial poultry companies in the United States recently established that non-toxic water-based foam with a certain bubble size presents a practicable, effective and humane method for mass depopulation. Foam of the right bubble size creates an occlusion in the trachea of birds, causing a rapid onset of hypoxia. The foam that blankets the broiler house induces physical hypoxia - the same cause of death as the approved method using carbon dioxide gas (CO(2)). The article illustrates the different culling and disposal methods with a focus on the methods used during the 2003 H7N7 crisis in Belgium.

The challenge of avian influenza to the veterinary community

Avian influenza (AI) is a listed disease of the World Organisation for Animal Health (OIE) that has become a disease of great importance both for animal and human health. The increased relevance of AI in the fields of animal and human health has highlighted the lack of scientific information on several aspects of the disease, which has hampered the adequate management of some of the recent crises. Millions of animals have died, and there is growing concern over the loss of human lives and over the management of the pandemic potential. The present paper aims to identify areas of knowledge of veterinary competence that need to be improved in order to generate information to support the global AI crisis, and highlights the major changes in AI legislation, including regulations related to trade. It also reviews the human health implications of AI, including the mechanisms by which a human pandemic virus may be generated, and the food safety issues related to this infection. The application of control policies, ranging from stamping out to emergency and prophylactic vaccination, are discussed on the basis of data generated in recent outbreaks, and in the light of new regulations, also in view of the maintenance of good animal welfare. Poultry veterinarians working for the industry or for the public sector represent the first line of defence against the pandemic threat and for the prevention and control of this infection in poultry and in wild birds. However, given the current situation, it is imperative that close collaboration is sought and achieved by health officials involved in the veterinary, agricultural and medical aspects of the disease. Only through the exchange of data, experiences, views and information will it be possible to combat this zoonosis, which represents a major threat to public health and animal well-being.

Understanding the Complex Pathobiology of High Pathogenicity Avian Influenza Viruses in Birds

Avian influenza (AI) viruses are a diverse group of viruses that can be divided into 144 subtypes, based on different combinations of the 16 hemagglutinin and nine neuraminidase subtypes, and two pathotypes (low and high pathogenicity [HP]), based on lethality for the major poultry species, the chicken. However, other criteria are important in understanding the complex biology of AI viruses, including host adaptation, transmissibility, infectivity, tissue tropism, and lesion, and disease production. Overall, such pathobiological features vary with host species and virus strain. Experimentally, HPAI viruses typically produce a similar severe, systemic disease with high mortality in chickens and other gallinaceous birds. However, these same viruses usually produce no clinical signs of infection or only mild disease in domestic ducks and wild birds. Over the past decade, the emergent HPAI viruses have shifted to increased virulence for chickens as evident by shorter mean death times and a greater propensity for massive disseminated replication in vascular endothelial cells. Importantly, the Asian H5N1 HPAI viruses have changed from producing inconsistent respiratory infections in 2-wk-old domestic ducks to some strains being highly lethal in ducks with virus in multiple internal organs and brain. However, the high lethality for ducks is inversely related to age, unlike these viruses in gallinaceous poultry, which are highly lethal irrespective of the host age. The most recent Asian H5N1 HPAI viruses have infected some wild birds, producing systemic infections and death. Across all bird species, the ability to produce severe disease and death is associated with high virus replication titers in the host, especially in specific tissues such as brain and heart.

Coronaviruses in poultry and other birds

The number of avian species in which coronaviruses have been detected has doubled in the past couple of years. While the coronaviruses in these species have all been in coronavirus Group 3, as for the better known coronaviruses of the domestic fowl (infectious bronchitis virus [IBV], in Gallus gallus), turkey (Meleagris gallopavo) and pheasant (Phasianus colchicus), there is experimental evidence to suggest that birds are not limited to infection with Group 3 coronaviruses. In China coronaviruses have been isolated from peafowl (Pavo), guinea fowl (Numida meleagris; also isolated in Brazil), partridge (Alectoris) and also from a non-gallinaceous bird, the teal (Anas), all of which were being reared in the vicinity of domestic fowl. These viruses were closely related in genome organization and in gene sequences to IBV. Indeed, gene sequencing and experimental infection of chickens indicated that the peafowl isolate was the H120 IB vaccine strain, while the teal isolate was possibly a field strain of a nephropathogenic IBV. Thus the host range of IBV does extend beyond the chicken. Most recently, Group 3 coronaviruses have been detected in greylag goose (Anser anser), mallard duck (Anas platyrhynchos) and pigeon (Columbia livia). It is clear from the partial genome sequencing of these viruses that they are not IBV, as they have two additional small genes near the 3' end of the genome. Twenty years ago a coronavirus was isolated after inoculation of mice with tissue from the coastal shearwater (Puffinus puffinus). While it is not certain whether the virus was actually from the shearwater or from the mice, recent experiments have shown that bovine coronavirus (a Group 2 coronavirus) can infect and also cause enteric disease in turkeys. Experiments with some Group 1 coronaviruses (all from mammals, to date) have shown that they are not limited to replicating or causing disease in a single host. SARS-coronavirus has a wide host range. Clearly there is the potential for the emergence of new coronavirus diseases in domestic birds, from both avian and mammalian sources. Modest sequence conservation within gene 1 has enabled the design of oligonucleotide primers for use in diagnostic reverse transcriptase-polymerase chain reactions, which will be useful for the detection of new coronaviruses.

Performance of clinical signs in poultry for the detection of outbreaks during the avian influenza A (H7N7) epidemic in The Netherlands in 2003

The aim of this study was to make an inventory of the clinical signs of high-pathogenicity avian influenza (HPAI), to facilitate the development of an operational syndrome-reporting system (SRS) in The Netherlands as an early warning system for HPAI outbreaks. A total of 537 poultry flocks (240 infected and 297 non-infected) with a clinical suspicion of an infection with HPAI virus were investigated with respect to the clinical signs observed. Standardized reports were analysed with respect to observed clinical signs in the flocks. Various poultry types were distinguished. In infected commercial flocks with egg-producing chickens, the presence of increased mortality, apathy, coughing, reduction in normal vocalization, or pale eggs appeared to be overall the most sensitive indicators to detect a HPAI outbreak, matching a sensitivity of 99% with a specificity of 23%. In infected turkey flocks, the presence of apathy, decreased growth performance, reduction of normal vocalization, swollen sinuses, yawning, huddling, mucosal production from the beak, or lying down with an extended neck appeared to be overall the most sensitive indicators to detect a HPAI outbreak, matching a sensitivity of 100% with a specificity of 79%. In infected backyard/hobby flocks, increased mortality or swollen head appeared to be overall the most sensitive indicators of a HPAI outbreak, matching a sensitivity of 100% with a specificity of 26%. These results indicate that there is a solid basis for the choice of using increased mortality in the operational SRS in The Netherlands as an early warning system for HPAI outbreaks. The presence of apathy, specifically for turkeys, should be added to the SRS as an indicator.

A cross-sectional serological survey of the Dutch commercial poultry population for the presence of low pathogenic avian influenza virus infections

After the discovery of poultry infected with highly pathogenic avian influenza (HPAI) virus of subtype H7N7 in the central area of The Netherlands on 28 February 2003, the hypothesis was put forward that an outbreak of the low pathogenic (LP) variant of H7N7 had preceded, unnoticed, the occurrence of the HPAI virus. Consequently, a cross-sectional serological survey of the Dutch poultry population was executed in the second week of March 2003. The basic requirements set were detection of a 5% prevalence of flocks exposed to LPAI virus with 95% confidence within the production type stratification level within each province in The Netherlands. Because of supposed higher risk of avian influenza infections in ducks, turkeys and free-range poultry, all the commercial flocks of these production types present in The Netherlands were sampled. The serological screening of 28018 sera from 1193 randomly selected poultry farms, located outside surveillance zones showed that LPAI H7 virus infections had occurred on three neighbouring farms all located in the southwest of The Netherlands. No antibodies against the neuraminidase N7 subtype were detected in the sera of these farms, indicating that the subtype was different from the HPAI H7N7 subtype that caused the avian influenza epidemic in 2003. In addition, evidence of infections with non-H5 or non-H7 subtypes of influenza A virus were obtained in two other farms located in the northeast and the southeast of The Netherlands. It was concluded that the HPAI subtype H7N7 outbreak was most likely not preceded by a significant circulation of a LPAI subtype H7N7 virus. Based on the Dutch experience, recommendations are made to detect avian influenza infections faster in the future.