Partial heterologous protection by low pathogenic H9N2 virus against natural H9N2-PB1 gene reassortant highly pathogenic H5N1 virus in chickens

Experimental Infection and In-Contact Transmission of H9N2 Avian Influenza Virus in Crows

This study aimed to investigate the potential of H9N2 avian influenza virus to cause disease and intra-species transmission in house crows (Corvus splendens). A group of six crows were intranasally inoculated with 10^6.0 EID₅₀ of H9N2 virus (A/chicken/India/07OR17/2021), and 24 h post-inoculation six naïve crows were co-housed with infected crows. Crows were observed for 14 days for any overt signs of illness. Oropharyngeal and cloacal swabs were collected up to 14 days to assess virus excretion. No apparent clinical signs were observed in either infected or in-contact crows. Virus excretion was observed only in infected birds up to 9 days post-infection (dpi) through both oropharyngeal and cloacal routes. All six infected crows seroconverted to H9N2 virus at 14 dpi, whereas all in-contact crows remained negative to H9N2 virus antibodies. No virus could be isolated from tissues viz., lung, liver, kidney, pancreas, small intestine and large intestine. Although crows became infected with the H9N2 virus, transmission of the virus was inefficient to the in-contact group. However, virus excretion through oral and cloacal swabs from infected crows suggests a potential threat for inter-species transmission, including humans. Crows, being a common synanthrope species, might have some role in influenza virus transmission to poultry and humans, which needs to be explored further.

Induction profiles of mRNA of toll like receptors and cytokines in chickens pre-exposed to low pathogenic avian influenza H9N2 virus followed by challenge with highly pathogenic avian influenza H5N1 virus

Herein, the induction of TLRs and cytokines in chickens pre-exposed to low pathogenic avian influenza H9N2 virus followed by challenge with highly pathogenic avian influenza (HPAI) H5N1 virus was studied. Four groups (1-4) of chickens inoculated with 10⁶ EID₅₀ of H9N2 virus were challenged with 10⁶ EID₅₀ of H5N1 virus on days 1, 3, 7 and 14 post H9N2 inoculation, respectively. In groups (1-4) TLRs and cytokines induction was studied in chicken PBMCs on day 3 post H5N1 challenge. In H5N1 control group TLRs (1, 2, 5 and 7) cytokines (IFNα, IFNβ, IFNγ, IL1β, IL2, IL4, IL8 and TGF β3) were down regulated. In group 1 down regulation of cytokines and TLRs was similar to H5N1 control birds. Down regulation of TLRs and cytokines in H5N1 control and group 1 resulted death of all the chickens. In group 2, up-regulation of TLRs (3, 7 and 15) and induction of TNFα, IFNα, IFNβ, IFNγ aided virus clearance leading to survival of all the chickens. In group 3 significant up-regulation of TLRs (3, 4 and 15) and significant induction of cytokines (IFNγ, TNFα, IL1β, IL4, IL6, IL8, IL10 and TGF β3) was detected. In group 4 significant up-regulation of TLRs (2, 3, 7 and 15) and significant induction of cytokines (IFNγ, TNFα, IL1β, IL2, IL6, IL8 and IL10) was detected. In groups 3 and 4 simultaneous and significant induction of pro-inflammatory, antiviral and anti-inflammatory cytokine resulted cytokine dysregulation leading to death of (2/6) and (3/6) chickens respectively. Hence, the study revealed TLRs and cytokines role in modulating the H5N1 infection outcome in chickens pre-exposed to H9N2 virus.

Highly pathogenic avian influenza H5N1 virus induces cytokine dysregulation with suppressed maturation of chicken monocyte-derived dendritic cells

One of the major causes of death in highly pathogenic avian influenza virus (HPAIV) infection in chickens is acute induction of pro-inflammatory cytokines (cytokine storm), which leads to severe pathology and acute mortality. DCs and respiratory tract macrophages are the major antigen presenting cells that are exposed to mucosal pathogens. We hypothesized that chicken DCs are a major target for induction of cytokine dysregulation by H5N1 HPAIV. It was found that infection of chicken peripheral blood monocyte-derived dendritic cells (chMoDCs) with H5N1 HPAIV produces high titers of progeny virus with more rounding and cytotoxicity than with H9N2 LPAIV. Expression of maturation markers (CD40, CD80 and CD83) was weaker in both H5N1 and H9N2 groups than in a LPS control group. INF-α, -β and -γ were significantly upregulated in the H5N1 group. Pro-inflammatory cytokines (IL-1β, TNF-α and IL-18) were highly upregulated in early mid (IL-1), and late (IL-6) phases of H5N1 virus infection. IL-8 (CXCLi2) mRNA expression was significantly stronger in the H5N1 group from 6 hr of infection. TLR3, 7, 15 and 21 were upregulated 24 hr after infection by H5N1 virus compared with H9N2 virus, with maximum expression of TLR 3 mRNA. Similarly, greater H5N1 virus-induced apoptotic cell death and cytotoxicity, as measured by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling and lactate dehydrogenase assays, respectively, were found. Thus, both H5N1 and H9N2 viruses evade the host immune system by inducing impairment of chMoDCs maturation and enhancing cytokine dysregulation in H5N1 HPAIV-infected cells.