Newcastle disease: outbreak losses and control policy costs

Discovery of Avian Paramyxoviruses APMV-1 and APMV-6 in Shorebirds and Waterfowl in Southern Ukraine

Emerging RNA virus infections are a growing concern among domestic poultry industries due to the severe impact they can have on flock health and economic livelihoods. Avian paramyxoviruses (APMV; avulaviruses, AaV) are pathogenic, negative-sense RNA viruses that cause serious infections in the respiratory and central nervous systems. APMV was detected in multiple avian species during the 2017 wild bird migration season in Ukraine and studied using PCR, virus isolation, and sequencing. Of 4090 wild bird samples collected, mostly from southern Ukraine, eleven isolates were grown in ovo and identified for APMV serotype by hemagglutinin inhibition test as: APMV-1, APMV-4, APMV-6, and APMV-7. To build One Health's capacity to characterize APMV virulence and analyze the potential risks of spillover to immunologically naïve populations, we sequenced virus genomes in veterinary research labs in Ukraine using a nanopore (MinION) platform. RNA was extracted and amplified using a multiplex tiling primer approach to specifically capture full-length APMV-1 (n = 5) and APMV-6 (n = 2) genomes at high read depth. All APMV-1 and APMV-6 fusion (F) proteins possessed a monobasic cleavage site, suggesting these APMVs were likely low virulence, annually circulating strains. Utilization of this low-cost method will identify gaps in viral evolution and circulation in this understudied but important critical region for Eurasia.

Insights into Genomic Epidemiology, Evolution, and Transmission Dynamics of Genotype VII of Class II Newcastle Disease Virus in China

Newcastle disease virus (NDV) is distributed worldwide and has caused significant losses to the poultry industry. Almost all virulent NDV strains belong to class II, among which genotype VII is the predominant genotype in China. However, the molecular evolution and phylodynamics of class II genotype VII NDV strains in China remained largely unknown. In this study, we identified 13 virulent NDV including 11 genotype VII strains and 2 genotype IX strains, from clinical samples during 1997 to 2019. Combined NDV sequences submitted to GenBank, we investigate evolution, and transmission dynamics of class II NDVs in China, especially genotype VII strains. Our results revealed that East and South China have the most genotypic diversity of class II NDV, and East China might be the origin of genotype VII NDVs in China. In addition, genotype VII NDVs in China are presumably transmitted by chickens, as the virus was most prevalent in chickens. Furthermore, codon usage analysis revealed that the F genes of genotype VII NDVs have stronger adaptation in chickens, and six amino acids in this gene are found under positive selection via selection model analysis. Collectively, our results revealed the genetic diversity and evolutionary dynamics of genotype VII NDVs in China, providing important insights into the epidemiology of these viruses in China.

Phylodynamic analyses of class I Newcastle disease virus isolated in China

Newcastle disease virus (NDV), the pathogen of Newcastle disease, has caused significant losses to the poultry industry worldwide. However, owing to its avirulence, class I NDVs have not been studied as much as class II NDVs. We aimed to epidemiologically monitor the spread of class I NDVs in China. We isolated 104 class I NDV strains from poultry in live poultry markets (LPMs) of Guangdong Province, south China, between January 2016 and December 2018. Genetic analysis revealed that all 104 isolates and most of the strains isolated from China were clustered into genotype 1.1.2 of class I NDVs. Bayesian analysis revealed that, although the United States may be the source, east and south China may be the epicentres of class I NDVs in China. In addition, in China, class I NDVs are presumably transmitted by chickens and domestic ducks as the virus is mostly prevalent in these birds. These novel findings demonstrated that class I NDVs are prevalent in south China, and it is important to perform routine surveillance and limit the numbers of different birds in different areas of LPMs to decrease the risk of intra- and interspecies transmission of NDVs.

Global phylodynamic analysis of avian paramyxovirus-1 provides evidence of inter-host transmission and intercontinental spatial diffusion

BACKGROUND

Avian avulavirus (commonly known as avian paramyxovirus-1 or APMV-1) can cause disease of varying severity in both domestic and wild birds. Understanding how viruses move among hosts and geography would be useful for informing prevention and control efforts. A Bayesian statistical framework was employed to estimate the evolutionary history of 1602 complete fusion gene APMV-1 sequences collected from 1970 to 2016 in order to infer viral transmission between avian host orders and diffusion among geographic regions. Ancestral states were estimated with a non-reversible continuous-time Markov chain model, allowing transition rates between discrete states to be calculated. The evolutionary analyses were stratified by APMV-1 classes I (n = 198) and II (n = 1404), and only those sequences collected between 2006 and 2016 were allowed to contribute host and location information to the viral migration networks.

RESULTS

While the current data was unable to assess impact of host domestication status on APMV-1 diffusion, these analyses supported the sharing of APMV-1 among divergent host taxa. The highest supported transition rate for both classes existed from domestic chickens to Anseriformes (class I:6.18 transitions/year, 95% highest posterior density (HPD) 0.31-20.02, Bayes factor (BF) = 367.2; class II:2.88 transitions/year, 95%HPD 1.9-4.06, BF = 34,582.9). Further, among class II viruses, domestic chickens also acted as a source for Columbiformes (BF = 34,582.9), other Galliformes (BF = 34,582.9), and Psittaciformes (BF = 34,582.9). Columbiformes was also a highly supported source to Anseriformes (BF = 322.0) and domestic chickens (BF = 402.6). Additionally, our results provide support for the diffusion of viruses among continents and regions, but no interhemispheric viral exchange between 2006 and 2016. Among class II viruses, the highest transition rates were estimated from South Asia to the Middle East (1.21 transitions/year; 95%HPD 0.36-2.45; BF = 67,107.8), from Europe to East Asia (1.17 transitions/year; 95%HPD 0.12-2.61; BF = 436.2) and from Europe to Africa (1.06 transitions/year, 95%HPD 0.07-2.51; BF = 169.3).

CONCLUSIONS

While migration appears to occur infrequently, geographic movement may be important in determining viral diversification and population structure. In contrast, inter-order transmission of APMV-1 may occur readily, but most events are transient with few lineages persisting in novel hosts.

Parthenogenesis in birds: a review

Parthenogenesis or 'virgin birth' is embryonic development in unfertilized eggs. It is a routine means of reproduction in many invertebrates. However, even though parthenogenesis occurs naturally in even more advanced vertebrates, like birds, it is mostly abortive in nature. In fact, multiple limiting factors, such as delayed and unorganized development as well as unfavorable conditions developing within the unfertilized egg upon incubation, are associated with termination of progressive development of parthenogenetic embryos. In birds, diploid parthenogenesis is automictic and facultative producing only males. However, the mechanisms controlling parthenogenesis in birds are not clearly elucidated. Additionally, it appears from even very recent research that these mechanisms may hinder the normal fertilization process and subsequent embryonic development. For instance, virgin quail and turkey hens exhibiting parthenogenesis have reduced reproductive performance following mating. Also, genetic selection and environmental factors, such as live virus vaccinations, are known to trigger the process of parthenogenesis in birds. Therefore, parthenogenesis has a plausible negative impact on the poultry industry. Hence, a better understanding of parthenogenesis and the mechanisms that control it could benefit commercial poultry production. In this context, the aim of this review is to provide a complete overview of the process of parthenogenesis in birds.

The role of the bursa of Fabricius in the immune response to vaccinal antigens and the development of immune tolerance in chicks (Gallus domesticus) vaccinated at a very young age

Vaccination is recognized to be the most cost-effective means of preventing, controlling, and even eradicating infectious diseases. Conventional poultry are vaccinated through various routes including eye/nose drops, drinking water, vent brush, or injection. Efficient vaccination is an essential part of any good poultry management.The bursa of Fabricius is intimately connected to the cloaca and the intestinal system. It is well-known as a primary lymphoid organ in the chicken and a major channel through which environmental antigens stimulate the immune system. In this study we tested whether direct instillation of various viral vaccines and antigens into the cloaca (per bursam), could stimulate higher antibody titers and generate improved protection. Despite the very rapid absorption of the vaccines or antigens from the cloaca to the lumen of the Bursa of Fabricius, per bursam inoculation failed to generate a satisfactory immune response. In contrast conventional administration of live or inactivated commercial vaccines led to an acceptable level of seroconversion and protection against challenge.An interesting finding in this study was the fact that administration of a single priming dose of antigenic material at age 1 or 5 days, did not improve the response to a second administration at 14 days of age as expected. Instead, in most cases there was a reduced serum antibody response suggesting the induction of tolerance. This was true for all routes of administration (intramuscular, per ocular and per bursam) and for all formulations of vaccine.The current study reveals: 1) no advantage for direct application of live or inactivated vaccines or antigens into the bursa of Fabricius compared to common routes of vaccination, 2) that apparent desensitization or tolerance effects have important implications for poultry management, since in many countries, vaccination of day old chicks is compulsory or a well-accepted part of flock vaccination.According to our results, early vaccination can in fact reduce or inhibit a secondary immune response to subsequent vaccination and increase susceptibility to disease agents.

Viscerotropic velogenic Newcastle disease virus replication in feathers of infected chickens

Newcastle disease viruses (NDVs) cause systemic diseases in chickens with high mortality. However, little is known about persistence of NDVs in contaminated tissues from infected birds. In this study, we examined viral replication in the feather pulp of chickens inoculated with viscerotropic velogenic NDV (vvNDV) genotype VII. Reverse transcription real-time PCR and immunohistochemistry were used to investigate viral persistence in the samples. vvNDV was detected in the oropharynx and cloaca and viral antigens were detected in the feathers, suggesting that feathers act as sources of viral transmission.

Mast cells and influenza a virus: association with allergic responses and beyond

Influenza A virus (IAV) is a widespread infectious agent commonly found in mammalian and avian species. In humans, IAV is a respiratory pathogen that causes seasonal infections associated with significant morbidity in young and elderly populations, and has a large economic impact. Moreover, IAV has the potential to cause both zoonotic spillover infection and global pandemics, which have significantly greater morbidity and mortality across all ages. The pathology associated with these pandemic and spillover infections appear to be the result of an excessive inflammatory response leading to severe lung damage, which likely predisposes the lungs for secondary bacterial infections. The lung is protected from pathogens by alveolar epithelial cells, endothelial cells, tissue resident alveolar macrophages, dendritic cells, and mast cells. The importance of mast cells during bacterial and parasitic infections has been extensively studied; yet, the role of these hematopoietic cells during viral infections is only beginning to emerge. Recently, it has been shown that mast cells can be directly activated in response to IAV, releasing mediators such histamine, proteases, leukotrienes, inflammatory cytokines, and antiviral chemokines, which participate in the excessive inflammatory and pathological response observed during IAV infections. In this review, we will examine the relationship between mast cells and IAV, and discuss the role of mast cells as a potential drug target during highly pathological IAV infections. Finally, we proposed an emerging role for mast cells in other viral infections associated with significant host pathology.

Agroterrorism targeting livestock: a review with a focus on early detection systems

Agroterrorism targeting livestock can be described as the intentional introduction of an animal disease agent against livestock with the purpose of causing economic damage, disrupting socioeconomic stability of a country, and creating panic and distress. This type of terrorism can be alluring to terrorists because animal disease agents are easily available. This review addresses the vulnerabilities of the livestock industry to agroterrorism. However, we also show that early detection systems have recently been developed for agroterrorism and deliberate spread of animal pathogens in livestock, including an agroterrorism intelligence cycle, syndromic surveillance programs, and computer-based clinical decision support systems that can be used for early detection of notifiable animal diseases. The development of DIVA-vaccines in the past 10 to 15 years has created, in principle, an excellent response instrument to counter intentional animal disease outbreaks. These developments have made our animal agriculture less vulnerable to agroterrorism. But we cannot relax; there are still many challenges, in particular with respect to integration of first line of defense, law enforcement, and early detection systems for animal diseases.

Newcastle disease in the European Union 2000 to 2009

Newcastle disease (ND) is a devastating disease of poultry that has to some extent been neglected by those working in the field in the past 10 to 15 years while attention has been focused on the emergence and spread of highly pathogenic avian influenza caused by a H5N1 subtype virus. During 2000 to 2009 in the European Union (EU) member states, ND viruses virulent for chickens have been detected in wild birds, domesticated pigeons and poultry. Based on these isolations it appears that the epizootic in racing pigeons caused by the variant viruses termed pigeon avian paramyxovirus type 1, which form the genetic group 4b(VIb) first seen in Europe in 1981, continued during 2000 to 2009, and the virus is probably enzootic in racing pigeons in some EU countries. This virus appears to have spread regularly to wild birds, especially those of the Columbidae family, and has been the cause of significant outbreaks in poultry. Other avian paramyxovirus type 1 viruses responsible for ND outbreaks in the EU during 2000 to 2009 have been those from genetic groups 5b(VIIb) and 5d(VIId). There is evidence that the former may well represent spread from a wild bird source and these viruses have also been isolated from wild birds, while the latter represents continuing spread from the East. Future legislation or recommendations aimed at the control and eradication of ND will need to encompass these three sources of virulent ND viruses.

Exchange of Newcastle disease viruses in Korea: the relatedness of isolates between wild birds, live bird markets, poultry farms and neighboring countries

Newcastle disease virus (NDV) has a worldwide distribution and is often carried by wild ducks, which may represent one of the natural reservoirs. However, the epidemiological relatedness of NDV between wild ducks and domestic poultry is unclear. A total of 14 isolates were obtained from 8439 samples from live bird markets (LBMs) and wild bird populations in Korea during from 2007 to 2010. These isolates were characterized genetically and phylogenetic analysis was conducted to investigate the relatedness between isolates from wild birds, LBM and poultry farms. In phylogenetic analysis, all 14 isolates belonged to genotype I virus within class II. Of these, nine isolates from wild birds were most closely related to the Aomori-like cluster. The five LBM isolates were most closely related to the V4-like cluster. All isolates in this study were closely related to isolates from domestic duck farms in Korea and Chinese LBM isolates. The results indicate that NDV exchange occurs between wild birds, poultry farms, LBMs and neighboring countries. Enhanced NDV surveillance is required to monitor the introduction of variant NDV in consequence of evolution in LBMs and to investigate NDV epidemiology in various species of putative hosts.

Increased mast cell density during the infection with velogenic Newcastle disease virus in chickens

In addition to their well-characterized role in allergic inflammation, recent data confirm that mast cells play a more extensive role in a variety of viral infections. The contribution of mast cells to Newcastle disease pathogenesis has not been investigated. We evaluated mast cell activity after Newcastle disease virus (NDV) infection in specific pathogen free chickens using cytochemical and immunocytochemical analyses. The results were as follows. Severe tissue damage was observed in the proventriculus, duodenum, jejunum and caecal tonsil, and NDV antigens were detected and presented extensively in these tissues. Second, in the NDV-infected group, the mast cell population was increased markedly in the proventriculus, duodenum, jejunum and caecal tonsil at 24, 48, 72 and 96 h after infection (P<0.01). However, very few mast cells were observed in those same tissues in the control. More intriguingly, the greatest number of mast cells was found in the proventriculus, which also showed the greatest level of NDV antigens. Third, the content of tryptase was significantly higher (P<0.01) in the NDV-infected group compared with the control from 24 to 96 h post infection). Furthermore, as an important protease released by mast cells, tryptase had a positive correlation with mast cell distribution. These data indicated that mast cells were involved in the response to NDV. Our results also suggested that the broad range of mast cell mediators might have a role in the pathology of Newcastle disease.

Neighbourhood control policies and the spread of infectious diseases

We present a model of a control programme for a disease outbreak in a population of livestock holdings. Control is achieved by culling infectious holdings when they are discovered and by the pre-emptive culling of livestock on holdings deemed to be at enhanced risk of infection. Because the pre-emptive control programme cannot directly identify exposed holdings, its implementation will result in the removal of both infected and uninfected holdings. This leads to a fundamental trade-off: increased levels of control produce a greater reduction in transmission by removing more exposed holdings, but increase the number of uninfected holdings culled. We derive an expression for the total number of holdings culled during the course of an outbreak and demonstrate that there is an optimal control policy, which minimizes this loss. Using a metapopulation model to incorporate local clustering of infection, we examine a neighbourhood control programme in a locally spreading outbreak. We find that there is an optimal level of control, which increases with increasing basic reproduction ratio, R(0); moreover, implementation of control may be optimal even when R(0) < 1. The total loss to the population is relatively insensitive to the level of control as it increases beyond the optimal level, suggesting that over-control is a safer policy than under-control.

Detection and differentiation of pathogenicity of avian paramyxovirus serotype 1 from field cases using one-step reverse transcriptase-polymerase chain reaction

Amplification of avian paramyxovirus serotype 1 (APMV-1)-specific nucleic acid fragments, followed by restriction endonuclease analysis (REA) using BglI, was carried out to type strains according to their virulence. Primer sequences were used to amplify a 202 base pair fragment, encompassing the fusion protein cleavage site, in a one-step reverse transcriptase-polymerase chain reaction (RT-PCR) test for detection of a range of field cases and reference strains of APMV-1. Subsequent REA of the amplified fragments enabled differentiation of low virulent lentogenic field and vaccine strains from more virulent mesogenic and velogenic field strains of APMV-1, including pigeon PMV-1. In the present paper, we report the development and application of a one-step RT-PCR test coupled with REA as a fast, specific method for both the detection and typing of APMV-1 from field samples.

Gordon Memorial Lecture. Newcastle disease

1. In this paper several historical and contemporary aspects of Newcastle disease (ND) are reviewed, with particular reference to the greater understanding which modern techniques have allowed. 2. Virulent ND viruses were generally thought to have emerged in 1926 as a result of transfer from a wild bird host reservoir but there is evidence that the virulent virus may have existed in poultry before 1926. Recent findings suggest that the virulent virus may emerge in poultry as a result of mutations in viruses of low virulence. 3. The history of ND in Great Britain reflects the four known panzootics that have occurred and serves as a model for the impact this disease may have on poultry populations. 4. Attempts to control and eradicate ND are not as straightforward as it may appear; in particular vaccination, while preventing deaths and disease, on challenge may not prevent virus replication and could therefore lead to the virulent virus becoming endemic. 5. Village chickens are extremely important assets in most developing countries, representing a significant source of protein in the form of eggs and meat but endemic ND can cause mortality of up to 60% in village chickens.