Interaction between avian influenza subtype H9N2 and Newcastle disease virus vaccine strain (LaSota) in chickens

Modelling the transmission dynamics of H9N2 avian influenza viruses in a live bird market

H9N2 avian influenza viruses (AIVs) are a major concern for the poultry sector and human health in countries where this subtype is endemic. By fitting a model simulating H9N2 AIV transmission to data from a field experiment, we characterise the epidemiology of the virus in a live bird market in Bangladesh. Many supplied birds arrive already exposed to H9N2 AIVs, resulting in many broiler chickens entering the market as infected, and many indigenous backyard chickens entering with pre-existing immunity. Most susceptible chickens become infected within one day spent at the market, owing to high levels of viral transmission within market and short latent periods, as brief as 5.3 hours. Although H9N2 AIV transmission can be substantially reduced under moderate levels of cleaning and disinfection, effective risk mitigation also requires a range of additional interventions targeting markets and other nodes along the poultry production and distribution network.

Live IBD vaccine exacerbates disease and pathological effects of Asian lineage H9N2 LPAIV in chickens

Avian influenza H9N2 is one of the most commonly circulating viruses in numerous Egyptian poultry farms. The Asian lineage H9N2 exhibits an immunosuppressive effect, and its pathogenicity is amplified when it co-infects with other pathogens, especially with the immunosuppressive infectious bursal disease virus (IBDV), resulting in increased mortality rates. Both vaccines and field infection can exacerbate the pathogenicity of H9N2, particularly in the bursa of Fabricius, causing more significant lymphoid depletion. To comprehend the impact of the IBD vaccine on the viral and pathogenic effect of H9N2 infection in specific pathogen-free chicks (SPF), the experiment was designed as four groups; group 1 served as the negative control, group 2 received (228E) IBD vaccine, group 3 was challenged with H9N2, and group-4 was vaccinated by the IBD vaccine then challenged with H9N2. The clinical signs, relative immune organs weights and histopathological lesion scores were recorded. The tracheal and cloacal H9N2 viral shedding were also measured. Group 4 exhibited a significant decrease (P ≤ 0.05) in the relative bursal weight and an increase in the bursal lesion score when compared with groups 1 and 3 at 4 and 8 days post-challenge (dpc). The tracheal lesion score of group-4 recorded a significant increase when compared with groups 1 and 3. The renal lesion score of group 4 achieved a significant increase when compared with 1 and 3 at 8 dpc. Also, group 4 recorded a significant increase in H9N2 shedding in comparison with groups 1 and 3. Consequently, our study concluded that routine vaccination with the IBD intermediate plus vaccine exacerbates the silent infection of H9N2 resulting in outbreaks.

The beneficial effects of spraying of probiotic Bacillus and Lactobacillus bacteria on broiler chickens experimentally infected with avian influenza virus H9N2

This study investigated the clinical, antiviral, and immunological effects of spraying Bacillus spp. and Lactobacillus spp. as a single or mixture probiotic compound on experimentally infected broiler chickens with AIV H9N2. Two hundred and forty 1-day-old broilers were randomly assigned to 6 groups as follows: Ctrl- (no challenge AIV; no spray probiotic), Ctrl+ (AIV challenged; no spray probiotic), AI+B (AIV challenged; daily spraying of probiotic Bacillus spp.), AI+L group (AIV challenged; daily spraying of probiotic Lactobacillus spp.), AIV+BL (AIV challenged; daily spraying of probiotic Bacillus spp. and Lactobacillus spp.), and G-DW (daily spraying of normal saline; no AIV challenged). The birds were reared for 35 d. On the 22nd day of age, broiler chickens were challenged by AIV H9N2. The probiotics were sprayed at 9×10⁹ CFU/m² daily for 35 d. Growth performance, clinical signs, virus shedding, macroscopic and microscopic lesions were evaluated at various days in all groups. Spraying with probiotics improved the body weight gain and food conversion ratio in the AI+B, AI+L, and AI+BL groups compared to the Ctrl+. The severity of clinical signs, gross lesions, pathological lesions and viral shedding in the probiotic treatment groups was lower than in the Ctrl+ group. The findings of this study suggest the daily spraying of Lactobacillus and Bacillus probiotics alone or in combination during the rearing period reduce clinical and nonclinical aspects of H9N2 virus infection; so, it can be effective as a preventive protocol for controlling the severity of AIV H9N2 infection in broilers.

Common viral and bacterial avian respiratory infections: an updated review

Many pathogens that cause chronic diseases in birds use the respiratory tract as a primary route of infection, and respiratory disorders are the main leading source of financial losses in the poultry business. Respiratory infections are a serious problem facing the poultry sector, causing severe economic losses. Avian influenza virus, Newcastle disease virus, infectious bronchitis virus, and avian pneumovirus are particularly serious viral respiratory pathogens. Mycoplasma gallisepticum, Staphylococcus, Bordetella avium, Pasteurella multocida, Riemerella anatipestifer, Chlamydophila psittaci, and Escherichia coli have been identified as the most serious bacterial respiratory pathogens in poultry. This review gives an updated summary, incorporating the latest data, about the evidence for the circulation of widespread, economically important poultry respiratory pathogens, with special reference to possible methods for the control and prevention of these pathogens.

Roles for Pathogen Interference in Influenza Vaccination, with Implications to Vaccine Effectiveness (VE) and Attribution of Influenza Deaths

Pathogen interference is the ability of one pathogen to alter the course and clinical outcomes of infection by another. With up to 3000 species of human pathogens the potential combinations are vast. These combinations operate within further immune complexity induced by infection with multiple persistent pathogens, and by the role which the human microbiome plays in maintaining health, immune function, and resistance to infection. All the above are further complicated by malnutrition in children and the elderly. Influenza vaccination offers a measure of protection for elderly individuals subsequently infected with influenza. However, all vaccines induce both specific and non-specific effects. The specific effects involve stimulation of humoral and cellular immunity, while the nonspecific effects are far more nuanced including changes in gene expression patterns and production of small RNAs which contribute to pathogen interference. Little is known about the outcomes of vaccinated elderly not subsequently infected with influenza but infected with multiple other non-influenza winter pathogens. In this review we propose that in certain years the specific antigen mix in the seasonal influenza vaccine inadvertently increases the risk of infection from other non-influenza pathogens. The possibility that vaccination could upset the pathogen balance, and that the timing of vaccination relative to the pathogen balance was critical to success, was proposed in 2010 but was seemingly ignored. Persons vaccinated early in the winter are more likely to experience higher pathogen interference. Implications to the estimation of vaccine effectiveness and influenza deaths are discussed.

Intranasal Immunization with a Recombinant Avian Paramyxovirus Serotypes 2 Vector-Based Vaccine Induces Protection against H9N2 Avian Influenza in Chicken

Commercial inactivated vaccines against H9N2 avian influenza (AI) have been developed in China since 1990s and show excellent immunogenicity with strong HI antibodies. However, currently approved vaccines cannot meet the clinical demand for a live-vectored vaccine. Newcastle disease virus (NDV) vectored vaccines have shown effective protection in chickens against H9N2 virus. However, preexisting NDV antibodies may affect protective efficacy of the vaccine in the field. Here, we explored avian paramyxovirus serotype 2 (APMV-2) as a vector for developing an H9N2 vaccine via intranasal delivery. APMV-2 belongs to the same genus as NDV, distantly related to NDV in the phylogenetic tree, based on the sequences of Fusion (F) and hemagglutinin-neuraminidase (HN) gene, and has low cross-reactivity with anti-NDV antisera. We incorporated hemagglutinin (HA) of H9N2 into the junction of P and M gene in the APMV-2 genome by being flanked with the gene start, gene end, and UTR of each gene of APMV-2-T4 to generate seven recombinant APMV-2 viruses rAPMV-2/HAs, rAPMV-2-NPUTR-HA, rAPMV-2-PUTR-HA, rAPMV-2-FUTR-HA, rAPMV-2-HNUTR-HA, rAPMV-2-LUTR-HA, and rAPMV-2-MUTR-HA, expressing HA. The rAPMV-2/HAs displayed similar pathogenicity compared with the parental APMV-2-T4 virus and expressed HA protein in infected CEF cells. The NP-UTR facilitated the expression and secretion of HA protein in cells infected with rAPMV-2-NPUTR-HA. Animal studies demonstrated that immunization with rAPMV-2-NPUTR-HA elicited effective H9N2-specific antibody (6.14 ± 1.2 log2) responses and conferred complete immune protection to prevent viral shedding in the oropharyngeal and cloacal swabs from chickens challenged with H9N2 virus. This study suggests that our recombinant APMV-2 virus is safe and immunogenic and can be a useful tool in the combat of H9N2 outbreaks in chicken.

Poly (lactic-co-glycolic acid) nanoparticle-based vaccines delivery systems as a novel adjuvant for H9N2 antigen enhance immune responses

Poly (lactic-co-glycolic acid) (PLGA) nanoparticle used as vaccine adjuvants have been widely investigated due to their safety, antigen slow-release ability, and good adjuvants activity. In this study, immunopotentiator Alhagi honey polysaccharide encapsulated PLGA nanoparticles (AHPP) and assembled pickering emulsion with AHPP as shell and squalene as core (PPAS) were prepared. Characterization of AHPP and PPAS were investigated. H9N2 absorbed nanoparticles formulations were immunized to chicken, then the magnitude and kinetics of antibody and cellular immune responses were assessed. Our results showed that PPAS had rough strawberry-like surfaces, a large number of antigens could be absorbed on their surfaces through simple mixing. Adjuvant activity of PPAS showed that, PPAS/H9N2 can induce long-lasting and high HI titers, high thymus, spleen, and bursa of fabricius organ index. Moreover, chicken immunized with PPAS/H9N2 showed a mixed high differentiation of CD4⁺ and CD8a⁺ T cell, and strong Th1 and Th2-type cytokines mRNA expression. Thus, these findings demonstrated that PPAS could induce a strong and long-term cellular and humoral immune response, and has the potential to serve as an effective vaccine delivery adjuvant system for H9N2 antigen.

Protective Efficacy Evaluation of Four Inactivated Commercial Vaccines Against Low Pathogenic Avian Influenza H9N2 Virus Under Experimental Conditions in Broiler Chickens

Avian influenza vaccines are commonly used in the poultry industry. The objective of this study was to compare, under experimental conditions, the protective efficacy of four imported commercial inactivated H9N2 vaccines (A, B, C, and D) in broiler chickens. A total of 150 one-day-old chicks were divided into six groups: four experimental groups, each containing 30 chicks, received one of the vaccines (A, B, C, or D) delivered in a 0.3-ml dose subcutaneously at 1 day of age, whereas the control, Group T, was not vaccinated but challenged and Group E was kept unvaccinated and unchallenged. At 21 days postvaccination, Groups A, B, C, D, and T were challenged with 10⁷ embryo infective dose 50% of A/Chicken/Morocco/01/2016 (H9N2). All chicks were observed daily for clinical signs during the 12 days postchallenge (dpc). At 5 and 12 dpc, chicks were euthanatized for necropsy examination. Blood samples were collected weekly for serologic analysis and oropharyngeal swabs were collected for virus detection by real-time RT-PCR. Respiratory signs started at 48 hr pc and maximum severity was observed on 9 dpc. Chiefly, the birds vaccinated with vaccine B showed significantly more respiratory signs than did their counterparts. Serologic analysis revealed that the sera of Groups A and D birds showed a decrease in antibody (Ab) levels up to day 26; then a slight increase of Ab level was observed until day 31, while Group B and C birds showed a stabilization of the titers from day 21 until the end of the experiment. The viral shedding rate was significantly lower in Groups C and A (40%-50% of the birds shed virus for <7 days) compared with other challenged groups (60%-75% of the birds shed virus for ≥9 days). This experiment illustrated that vaccination applied on the first day in the hatchery with the four vaccines tested did not provide an acceptable protection against H9N2 in comparison with the controls that did not receive any vaccine. However, at first glance, we might favor vaccines A and C for their ability to reduce and shorten viral shedding as compared with vaccines B and D.

Effect of Newcastle disease and infectious bronchitis live vaccines on the immune system and production parameters of experimentally infected broiler chickens with H9N2 avian influenza

H9N2 Avian influenza (AI) is an infectious disease which considered to have low pathogenic virulence, but in the case of coinfection with other pathogens it has the potential to become a major threat to the poultry industry. Infectious bronchitis (IB) and Newcastle diseases (ND) are other common problems to the poultry industry, which there are an extensive vaccination program against these viral pathogens. To investigate the effects of administration of infectious bronchitis and Newcastle disease live vaccines (IBLVs and NDLVs) in the presence of H9N2 AI infection on the immune system and some production parameters, 180 one-day-old broiler chicks were randomly allocated into six groups with different vaccination programs including H120 IBLV, 4/91 IBLV, B1 NDLV and LaSota NDLV. At the age of 20 days, all birds of the experimental groups except the negative control group, were inoculated intra-nasally (at dose of 106 EID50) with H9N2 AIV. After the inoculation, gross and microscopic lesions of the immune organs, serological changes and some production parameters were examined. The findings of this study showed that coinfection of H9N2 AI with NDLVs exacerbated the gross and microscopic injuries in the immune organs; especially the bursa of Fabricius. LaSota + AIV group had the most severe lesion in the bursa of Fabricius, spleen and thymus. Furthermore, the birds of LaSota + AIV group consumed the least amount of feed and water and their final body weight were significantly (P ≤ 0.05) lower in comparison with the other groups. Interestingly, in the context of this experiment both 4/91 and H120 IB live vaccines enhanced the HI antibody titers against H9N2 AIV, but the 4/91 showed the most significant (P ≤ 0.05) increase compared to the other experimental groups.

Quantitative evaluation of viral interference among Egyptian isolates of highly pathogenic avian influenza viruses (H5N1 and H5N8) with the lentogenic and velogenic Newcastle disease virus genotype VII in specific pathogen-free embryonated chicken eggs model

Background and Aim

Mixed infections of the highly pathogenic avian influenza virus (HPAIV) and Newcastle disease virus (NDV) are considered the most distressing problem of the poultry industry. The problem arises due to the influence of a hidden virus on the replication of another suspected virus. Consequently, misdiagnosis of the real cause of disease may become a source of infection for other healthy stock by transmission and dissemination of the hidden virus. This study aimed to determine the impact of HPAIV and NDV on each other in a specific pathogen-free embryonated chicken egg (SPF-ECE) model.

Materials and Methods

HPAIVs (H5N1 and H5N8) and NDVs [avirulent NDV [avNDV] and velogenic NDV [vNDV]) were inoculated into the allantois cavity of SPF-ECE with graded titers (2, 3, and 4 log₁₀ EID50) at 24 and 48 h of incubation, followed by the collection of allantoic fluid. A quantitative reverse transcription real-time polymerase chain reaction was used to determine the viral RNA copies of both viruses.

Results

Obvious interference was reported on the growth of NDVs when co-inoculated with AIVs. NDV RNA titers reduction ranged from <3 to 5 log₁₀ to complete suppression, but slight interference with the growth of AIVs occurred. H5N1 RNA titers showed <1-2 log₁₀ reduction when co-inoculated with vNDV compared with the H5N1 control. The interference impact of H5N8 was more powerful than that of H5N1, while vNDV showed more resistance for interference than the avNDV strain. On the other hand, interference of AIVs was not observed except when vNDV was inoculated before H5N1. The interfering impact was increased after 48 h of inoculation, whereas no titer of avNDV was detectable.

Conclusion

AIV strains had a powerful effect on NDV growth, regardless of which infection occurred first.

Study of the underlying mechanisms and consequences of pathogenicity differences between two in vitro selected G1-H9N2 clones originating from a single isolate

The G1-H9N2 avian influenza virus (AIV) has caused significant economic losses in the commercial poultry industry due to reduced egg production and increased mortality. The field observations have shown that H9N2 viruses circulate and naturally mix with other pathogens and these simultaneous infections can exacerbate disease. To avoid an incorrect virus characterization, due to co-infection, isolates were purified by in vitro plaque assays. Two plaque purified G1-H9N2 clones, selected on different cell types, named MDCK-and CEF-clone in regards to the cell culture used, were studied in vivo, revealing two different virulence phenotypes. Subsequently, the underlying mechanisms were studied. Specifically, the phenotypical outcome of SPF bird infection by the two clones resulted in completely different clinical outcomes. These differences in clinical outcome were used to study the factors behind this output in more detail. Further studies demonstrated that the more severe disease outcome associated with the MDCK-clone involves a strong induction of pro-inflammatory cytokines and a lack of type I interferon production, whereas the mild disease outcome associated with the CEF-clone is related to a greater antiviral cytokine response. The immunosuppressive effect of the MDCK-clone on splenocytes was further demonstrated via ChIFN-γ lack production after ex vivo mitogenic stimulation. Genome sequencing of the two clones identified only four amino acid differences including three in the HA sequence (HA-E198A, HA-R234L, HA-E502D-H9 numbering) and one in the NA sequence (NA-V33M). In the present study, valuable insights on the mechanisms responsible for AI pathogenicity and molecular mechanisms of H9N2 infections in chicken were obtained while highlighting the impact of the cells viruses are grown on their virulence.