Enhanced pathogenicity of low-pathogenic H9N2 avian influenza virus after vaccination with infectious bronchitis live attenuated vaccine

Abstract

Aim:In the present study, two experiments were carried out for studying the pathogenicity of H9N2 avian influenza virus (AIV) in broiler chickens after vaccination with different live respiratory viral vaccines.Materials and Methods:One-day-old specific pathogen-free (SPF) chicks were divided into four groups in each experiment. In experiment 1, Groups 1 and 2 were inoculated with H9N2 AIV through nasal route in 1 day old, Groups 1 and 3 were vaccinated with live infectious bronchitis coronavirus (IBV) vaccine in 5 days old, and Group 4 was left as a negative control. In experiment 2, Groups 5 and 6 were inoculated with AIV subtype H9N2 through nasal route in 1 day old, Group 5 was vaccinated with live IBV vaccine and live Newcastle disease virus (NDV) vaccine in 5 and 18 days old, respectively, Groups 6 and 7 were vaccinated with live NDV vaccine in 18 days old, and Group 8 was left as a negative control. Chicks were kept in isolators for 18 days in the first experiment and 35 days in the second experiment. Tracheal and cloacal swabs were collected from 3, 5, 7, 10, 12, and 15 day’s old chicks from all groups in experiment 1 and 21, 23, 25, and 28 days old from all groups in experiment 2. Quantitative real-time reverse-transcriptase polymerase chain reaction (rRT-PCR) was applied on the collected tracheal swabs for detecting RNA copies of H9N2 AIV. Cloacal swabs and the positive rRT-PCR tracheal swabs were inoculated in 10-day-old SPF embryonated chicken eggs (ECE) to confirm rRT-PCR results. Internal organs (kidney, trachea, and spleen) from all chicken groups were collected weekly for histopathological examination to determine severity of the lesions. Serum samples were collected on a weekly basis for the detection of humoral immune response against H9N2, NDV, and IBV from all chicken groups.Results:rRT-PCR results with virus titration in ECEs revealed a significant increase in H9N2 AIV titer with extension in the period of viral shedding in Groups 1 and 5. Severe lesion score was observed for Groups 1 and 5. The humoral immune response against H9N2 AIV, NDV, and IBV revealed a significant increase in H9N2 AIV titer in Groups 1 and 5, NDV titer showed a significant increase in Group 7, and IBV titer increased in Groups 1, 3, and 5.Conclusion:Results demonstrated the increase in pathogenicity of H9N2 AIV, especially when H9N2-infected chicks vaccinated with live IBV vaccine.

Protective Efficacy of Different Live Attenuated Infectious Bronchitis Virus Vaccination Regimes Against Challenge With IBV Variant-2 Circulating in the Middle East

“…However, the cellular and local immune responses were found to positively correlate with the virulence of the vaccine strain (39). This correlation, despite enhancing protection, it greatly affects the suitability of such regimes in Egypt considering the exposure of vaccinated birds to multiple respiratory viral and/or bacterial pathogens interacting with IBV (2, 3, 48).…”

Co-infections of chickens with avian influenza virus H9N2 and Moroccan Italy 02 infectious bronchitis virus: effect on pathogenesis and protection conferred by different vaccination programmes

“…In contrast to these findings, co-infection with respiratory pathogens, such as IBV circulating in the field or live IBV vaccine, was shown to be one of the causes of increased virus pathogenicity and prolonged H9N2 viral shedding (Hassan et al, 2017;Ismail et al, 2018). Live IBV vaccine was indeed shown to provide proteases that increased the pathogenicity of AIV H9N2, due to a trypsin-like serine domain encoded by IBV (Liu et al, 1995;Ng & Liu, 2000).…”

“…AIV H9N2 is classified as a low pathogenic virus. However, high mortality has been reported in broiler farms in Morocco and in many other countries in Africa and Asia (Nili & Asasi, 2002Al-Garib et al, 2016;El Houadfi et al, 2016;Ismail et al, 2018). In Morocco, the low pathogenic avian influenza virus (LPAIV) subtype H9N2 was first identified in poultry in January 2016 and spread very quickly throughout the country (El Houadfi et al, 2016).…”

“…Likewise, co-infections of LPAIV H9N2 with other respiratory pathogens, particularly with IBV, Mycoplasma gallisepticum, Staphylococcus aureus, Avibacterium paragallinarum, Escherichia coli, Ornithobacterium rhinotracheale and/ or immunosuppressive agents can exacerbate LPAIV H9N2 infections and result in severe clinical disease with different rates of mortality (Nili & Asasi, 2002;Kishida et al, 2004;Perk et al, 2006). Previous studies have demonstrated longer H9N2 virus shedding, more severe clinical signs and higher mortality rates caused by a co-infection with LPAIV H9N2 and IBV, either as a vaccine or as a wild-type virus (Seifi et al, 2012;Hassan et al, 2017;Ismail et al, 2018).…”

Discrepancies in the efficacy of H5 inactivated avian influenza vaccines in specific-pathogen-free chickens against challenge with the Egyptian H5N8 clade 2.3.4.4 Group B virus isolated in 2018

“…To determine the histopathological changes caused by the challenge, we collected spleens and kidneys from each group at 3, 5, 7, and 10 days PC, fixed them in 10% formol saline embedded in paraffin, cut them into sections 4 μm thick, and stained the sections with hematoxylin and eosin [13]. We recorded and calculated pathological scores as previously reported by Gibson-Corley et al [14] for chicken groups challenged against A/chicken/Egypt/18FL6/2018(H5N8) virus due to variability in protection and shedding in those groups.…”