Elevated Complement Activation Fragments and C1q-Binding Circulating Immune Complexes in Varied Phases of Chikungunya Virus Infection.

Chikungunya virus (CHIKV) is a causative agent of a disease continuum, ranging from an acute transient chikungunya fever to chronic incapacitating viral arthralgia. The interaction between anti-CHIKV antibodies and the complement system has recently received attention. However, the contribution of complement activation in CHIKV-induced pathologies has not been fully elucidated. The present study was undertaken to delineate the possible contribution of complement activation in CHIKV-induced disease progression. In this study, using plasma specimens of chikungunya patients in the acute, chronic, and recovered phases of infection, we explicated the involvement of complement activation in CHIKV disease progression by ELISAs and Bio-Plex assays. Correlation analysis was carried out to demonstrate interrelation among C1q-binding IgG-containing circulating immune complexes (CIC-C1q), complement activation fragments (C3a, C5a, sC5b-9), and complement-modulated pro-inflammatory cytokines (IL-1ß, IL-18, IL-6, and TNF-α). We detected elevated complement activation fragments, CIC-C1q, and complement-modulated cytokines in the varied patient groups compared with the healthy controls, indicating persistent activation of the complement system. Furthermore, we observed statistically significant correlations among CIC-C1q with complement activation fragments and C3a with complement modulatory cytokines IL-1ß, IL-6, and IL-18 during the CHIKV disease progression. Taken together, the current data provide insight into the plausible association between CICs, complement activation, subsequent complement modulatory cytokine expression, and CHIKV etiopathology.

A novel reassortant avian influenza H4N6 virus isolated from an environmental sample during a surveillance in Maharashtra, India.

Background & objectives: Low pathogenic avian influenza (LPAI) viruses cause mild clinical illness in domestic birds. Migratory birds are a known reservoir for all subtypes of avian influenza (AI) viruses. The objective of the study was to characterize AI H4N6 virus isolated from an environmental sample during surveillance in Maharashtra, India. Methods: AI surveillance in wild migratory birds was conducted during the winter migratory bird season (2016-2017) in Pune, India. AI H4N6 virus was isolated from the faecal droppings of a wild migratory waterbird. Virological and molecular characterization of the isolated virus was carried out. Virus titration, haemagglutination inhibition assay, receptor specificity assay, intravenous pathogenicity index and neuraminidase inhibition assays were performed. Full genome sequencing, molecular and phylogenetic analyses were also conducted. Results: The virus was found to be of low pathogenicity, with avian type receptor specificity, and was susceptible to neuraminidase inhibitors. Phylogenetic and molecular analysis revealed that the present virus is a result of extensive reassortment with AI H8N4, H6N2, H4N3 and H3N6, predominantly as donor viruses among others. Interpretation & conclusions: This is the first report of the isolation and characterization of an LPAI H4N6 virus from an environmental sample from India. The present study showed that the H4N6 virus is a novel reassortant and divergent as compared with the reported H4N6 viruses from poultry in India, indicating independent introduction. This highlights the role of wild and migratory birds in the transmission of AI viruses and necessity of such studies at the human-animal interface.

Synergy between the classical and alternative pathways of complement is essential for conferring effective protection against the pandemic influenza A(H1N1) 2009 virus infection.

The pandemic influenza A(H1N1) 2009 virus caused significant morbidity and mortality worldwide thus necessitating the need to understand the host factors that influence its control. Previously, the complement system has been shown to provide protection during the seasonal influenza virus infection, however, the role of individual complement pathways is not yet clear. Here, we have dissected the role of intact complement as well as of its individual activation pathways during the pandemic influenza virus infection using mouse strains deficient in various complement components. We show that the virus infection in C3-/- mice results in increased viral load and 100% mortality, which can be reversed by adoptive transfer of naïve wild-type (WT) splenocytes, purified splenic B cells, or passive transfer of immune sera from WT, but not C3-/- mice. Blocking of C3a and/or C5a receptor signaling in WT mice using receptor antagonists and use of C3aR-/- and C5aR-/- mice showed significant mortality after blocking/ablation of C3aR, with little or no effect after blocking/ablation of C5aR. Intriguingly, deficiency of C4 and FB in mice resulted in only partial mortality (24%-32%) suggesting a necessary cross-talk between the classical/lectin and alternative pathways for providing effective protection. In vitro virus neutralization experiments performed to probe the cross-talk between the various pathways indicated that activation of the classical and alternative pathways in concert, owing to coating of viral surface by antibodies, is needed for its efficient neutralization. Examination of the virus-specific complement-binding antibodies in virus positive subjects showed that their levels vary among individuals. Together these results indicate that cooperation between the classical and alternative pathways not only result in efficient direct neutralization of the pandemic influenza virus, but also lead to the optimum generation of C3a, which when sensed by the immune cells along with the antigen culminates in generation of effective protective immune responses.

Amantadine resistance markers among low pathogenic avian influenza H9N2 viruses isolated from poultry in India, during 2009-2017.

Antiviral susceptibility screening of avian influenza (AI) H9N2 viruses is crucial considering their role at the animal-human interface and potential to cause human infections. The Matrix 2 (M2) inhibitors (amantadine and rimantadine) have been used for prophylaxis and treatment of influenza A virus infections, however, resistance to these drugs has been widely reported. Information about amantadine susceptibility of H9N2 viruses from India is scanty. Matrix genes of 48H9N2 viruses isolated from India during 2009-2017 were sequenced and M2 trans-membrane region sequences were screened for mutations which are known to confer resistance to amantadine namely, L26F, V27A, A30 T/V, S31N and G34E. All the viruses isolated during the year 2009 were sensitive to amantadine. However, resistance started to appear since the year 2010 and all the viruses isolated from the year 2015 onwards showed presence of molecular markers conferring resistance to amantadine. Majority of the resistant viruses exhibited S31 N mutation. Four isolates showed presence of V27A + S31 N dual mutations. Comparison of the M2 sequences from other Asian countries showed different patterns of amantadine resistance wherein phylogenetic analysis of the M genes of the strains from Pakistan formed a separate cluster. In conclusion, the present study reports prevalence and gradual increase of amantadine resistance among AI H9N2 viruses in India, emphasizing the importance of the antiviral surveillance.

A virus precipitation method for concentration & detection of avian influenza viruses from environmental water resources & its possible application in outbreak investigations.

Background & objectives: Avian influenza (AI) viruses have been a major cause of public health concern. Wild migratory birds and contaminated environmental sources such as waterbodies soiled with bird droppings play a significant role in the transmission of AI viruses. The objective of the present study was to develop a sensitive and user-friendly method for the concentration and detection of AI viruses from environmental water sources. Methods: Municipal potable water, surface water from reservoirs and sea were spiked with low pathogenic AI viruses. To concentrate the viruses by precipitation, a combination of potassium aluminium sulphate with milk powder was used. Real-time reverse transcription-polymerase chain reaction was performed for virus detection, and the results were compared with a virus concentration method using erythrocytes. Drinking water specimens from poultry markets were also tested for the presence of AI viruses. Results: A minimum of 101.0 EID50(50% egg infectious dose)/ml spiked H5N1 and 101.7 EID50/ml spiked H9N2 viruses were detected from spiked potable water; 101.0 and 102.0 EID50/ml spiked H5N1 virus was detected from surface water and seawater samples, respectively. The present method was more sensitive than the erythrocyte-binding method as approximately 10-fold higher infectious virus titres were obtained. AI H9N2 viruses were detected and isolated from water from local poultry markets, using this method. Interpretation & conclusions: Viability and recovery of the spiked viruses were not affected by precipitation. The present method may be suitable for the detection of AI viruses from different environmental water sources and can also be applied during outbreak investigations.

Differences in Type I interferon response in human lung epithelial cells infected by highly pathogenic H5N1 and low pathogenic H11N1 avian influenza viruses.

Influenza A virus infection induces type I interferons (IFNs α/ß) which activate host antiviral responses through a cascade of IFN signaling events. Herein, we compared highly pathogenic H5N1 and low pathogenic H11N1 avian influenza viruses isolated from India, for their replication kinetics and ability to induce IFN-ß and interferon-stimulating genes (ISGs). The H5N1 virus showed a higher replication rate and induced less IFN-ß and ISGs compared to the H11N1 virus when grown in the human lung epithelial A549 cells, reflecting the generation of differential innate immune responses during infection by these viruses. The non-structural 1 (NS1) protein, a major IFN-antagonist, known to help the virus in evading host innate immune response was compared from both the strains using bioinformatics tools. Analyses revealed differences in the composition of the NS1 proteins from the two strains that may have an impact on the modulation of the innate immune response. Intriguingly, H5N1 virus attenuated IFN-ß response in a non-NS1 manner, suggesting the possible involvement of other viral proteins (PB2, PA, PB1/PB1-F2) of H5N1 in synergy with NS1. Preliminary analyses of the above proteins of the two strains by sequence comparison show differences in charged residues. The insight gained will be useful in designing experimental studies to elucidate a probable role of the polymerase protein(s) in association with NS1 in inhibiting the IFN signaling and understanding the molecular mechanism governing the difference.

Mutational analysis of Kaposica reveals that bridging of MG2 and CUB domains of target protein is crucial for the cofactor activity of RCA proteins.

The complement system has evolved to annul pathogens, but its improper regulation is linked with diseases. Efficient regulation of the system is primarily provided by a family of proteins termed regulators of complement activation (RCA). The knowledge of precise structural determinants of RCA proteins critical for imparting the regulatory activities and the molecular events underlying the regulatory processes, nonetheless, is still limited. Here, we have dissected the structural requirements of RCA proteins that are crucial for one of their two regulatory activities, the cofactor activity (CFA), by using the Kaposi's sarcoma-associated herpesvirus RCA homolog Kaposica as a model protein. We have scanned the entire Kaposica molecule by sequential mutagenesis using swapping and site-directed mutagenesis, which identified residues critical for its interaction with C3b and factor I. Mapping of these residues onto the modeled structure of C3b-Kaposica-factor I complex supported the mutagenesis data. Furthermore, the model suggested that the C3b-interacting residues bridge the CUB (complement C1r-C1s, Uegf, Bmp1) and MG2 (macroglobulin-2) domains of C3b. Thus, it seems that stabilization of the CUB domain with respect to the core of the C3b molecule is central for its CFA. Identification of CFA-critical regions in Kaposica guided experiments in which the equivalent regions of membrane cofactor protein were swapped into decay-accelerating factor. This strategy allowed CFA to be introduced into decay-accelerating factor, suggesting that viral and human regulators use a common mechanism for CFA.

The evolution, characterization and phylogeography of avian influenza H9N2 viruses from India.

The low pathogenic avian influenza H9N2 virus is a significant zoonotic agent and contributes genes to highly pathogenic avian influenza (HPAI) viruses. H9N2 viruses are prevalent in India with a reported human case. We elucidate the spatio-temporal origins of the H9N2 viruses from India. A total of 30H9N2 viruses were isolated from poultry and environmental specimens (years 2015-2020). Genome sequences of H9N2 viruses (2003-2020) from India were analyzed, revealing several substitutions. We found five reassortant genotypes. The HA, NA and PB2 genes belonged to the Middle-Eastern B sublineage; NP and M to the classical G1 lineage; PB1, PA and NS showed resemblance to genes from either HPAI-H7N3/H5N1 viruses. Molecular clock and phylogeography revealed that the introduction of all the genes to India took place around the year 2000. This is the first report of the genesis and evolution of the H9N2 viruses from India, and highlights the need for surveillance.

Avian influenza surveillance reveals presence of low pathogenic avian influenza viruses in poultry during 2009-2011 in the West Bengal State, India.

INTRODUCTION: More than 70 outbreaks of the highly pathogenic avian influenza (HPAI) H5N1 have been reported in poultry in the western and north-eastern parts of India. Therefore, in view of the recent HPAI H5N1 outbreaks in poultry, active AI surveillance encompassing wild, resident, migratory birds and poultry was undertaken during 2009-2011 in the State of West Bengal. METHODS: A total of 5722 samples were collected from West Bengal; 3522 samples (2906 fecal droppings + 616 other environmental samples) were from migratory birds and 2200 samples [1604 tracheal, cloacal swabs, environmental samples, tissue samples + 596 blood (serum)] were from domestic ducks and poultry. All tracheal, cloacal and environmental samples were processed for virus isolation. Virus isolates were detected using hemagglutination assay and identified using hemagglutination inhibition (HI) and reverse transcriptase polymerase chain reaction (RT-PCR) assays. Sequencing and phylogenetic analysis of partial region of the hemagglutinin and neuraminidase genes was done. Intravenous pathogenicity index assays were performed in chickens to assess pathogenicity of AI virus isolates. Serum samples were tested for detection of antibodies against AI viruses using HI assay. RESULTS: A total of 57 AI H9N2, 15 AI H4N6 and 15 Newcastle Disease (NDV) viruses were isolated from chickens, from both backyard and wet poultry markets; AI H4N6 viruses were isolated from backyard chickens and domestic ducks. Characterization of AI H9N2 and H4N6 viruses revealed that they were of low pathogenicity. Domestic ducks were positive for antibodies against H5 and H7 viruses while chickens were positive for presence of antibodies against AI H9N2 and NDV. CONCLUSIONS: In the current scenario of HPAI H5N1 outbreaks in West Bengal, this report shows presence of low pathogenic AI H9N2 and H4N6 viruses in chickens and domestic ducks during the period 2009-2011. This is the first report of isolation of H4N6 from India. Antibodies against AI H5 and H7 in ducks highlight the probable role of domestic ducks in the transmission of AI viruses. Human infections of H9N2 have been reported from China and Hong Kong. This necessitates implementation of prevention and control measures to limit the spread of AI viruses.

Domain swapping reveals complement control protein modules critical for imparting cofactor and decay-accelerating activities in vaccinia virus complement control protein.

Vaccinia virus encodes a structural and functional homolog of human complement regulators named vaccinia virus complement control protein (VCP). This four-complement control protein domain containing secretory protein is known to inhibit complement activation by supporting the factor I-mediated inactivation of complement proteins, proteolytically cleaved form of C3 (C3b) and proteolytically cleaved form of C4 (C4b) (termed cofactor activity), and by accelerating the irreversible decay of the classical and to a limited extent of the alternative pathway C3 convertases (termed decay-accelerating activity [DAA]). In this study, we have mapped the VCP domains important for its cofactor activity and DAA by swapping its individual domains with those of human decay-accelerating factor (CD55) and membrane cofactor protein (MCP; CD46). Our data indicate the following: 1) swapping of VCP domain 2 or 3, but not 1, with homologous domains of decay-accelerating factor results in loss in its C3b and C4b cofactor activities; 2) swapping of VCP domain 1, but not 2, 3, or 4 with corresponding domains of MCP results in abrogation in its classical pathway DAA; and 3) swapping of VCP domain 1, 2, or 3, but not 4, with homologous MCP domains have marked effect on its alternative pathway DAA. These functional data together with binding studies with C3b and C4b suggest that in VCP, domains 2 and 3 provide binding surface for factor I interaction, whereas domain 1 mediates dissociation of C2a and Bb from the classical and alternative pathway C3 convertases, respectively.

In-silico screening and in-vitro assay show the antiviral effect of Indomethacin against SARS-CoV-2.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused the worldwide spread of coronavirus disease 19 (COVID-19), and till now, it has caused death to more than 6.2 million people. Although various vaccines and drug candidates are being tested globally with limited to moderate success, a comprehensive therapeutic cure is yet to be achieved. In this study, we applied computational drug repurposing methods complemented with the analyses of the already existing gene expression data to find better therapeutics in treatment and recovery. Primarily, we identified the most crucial proteins of SARS-CoV-2 and host human cells responsible for viral infection and host response. An in-silico screening of the existing drugs was performed against the crucial proteins for SARS-CoV-2 infection, and a few existing drugs were shortlisted. Further, we analyzed the gene expression data of SARS-CoV-2 in human lung epithelial cells and investigated the molecules that can reverse the cellular mRNA expression profiles in the diseased state. LINCS L1000 and Comparative Toxicogenomics Database (CTD) were utilized to obtain two sets of compounds that can be used to counter SARS-CoV-2 infection from the gene expression perspective. Indomethacin, a nonsteroidal anti-inflammatory drug (NSAID), and Vitamin-A were found in two sets of compounds, and in the in-silico screening of existing drugs to treat SARS-CoV-2. Our in-silico findings on Indomethacin were further successfully validated by in-vitro testing in Vero CCL-81 cells with an IC50 of 12 µM. Along with these findings, we briefly discuss the possible roles of Indomethacin and Vitamin-A to counter the SARS-CoV-2 infection in humans.

Application of frozen and stored glutaraldehyde-fixed turkey red blood cells for hemagglutination and hemagglutination inhibition assays for the detection and identification of influenza viruses.

INTRODUCTION: Hemagglutination (HA) and hemagglutination inhibition (HI) assays are conventionally used for the detection and identification of influenza viruses, using red blood cells (RBCs) from mammalian and avian sources. However, there could be limitations for availability of fresh RBCs due to situations such as pandemics, public health emergencies, outbreaks in avian species, lack of animal facilities, animal ethics concerns; or resource-constrained laboratories, and laboratories which do not carry out HA and HI assays routinely. Turkey RBCs (tRBCs) are widely used for HA and HI assays of influenza viruses. The present study explored the possibility of the use of glutaraldehyde-fixed tRBCs, which could be stored at -80 ºC and readily used for HA and HI assays. MATERIALS AND METHODS: A total of nine subtypes of human and avian influenza viruses, A H1N1, H3N2, H4N6, H5N1, H6N1, H7N9, H9N2, H11N1 and type B, were used in the study. Turkey RBCs were fixed with glutaraldehyde. The HA and HI assays were performed three times by two different operators using fresh and glutaraldehyde fixed tRBCs. The significance of difference in HA and HI titers between fixed and fresh RBCs was compared using 't-test'. The performance of fixed RBCs was evaluated before and after storing at -80 ºC for three weeks. RESULTS: There was no significant difference (p > 0.05) between mean HA and HI titers using fresh and glutaraldehyde-fixed turkey RBCs. In addition, the HA and HI titers using fixed tRBCs before and after storing at -80 ºC were equivalent, indicating suitability of the fixed and stored RBCs. CONCLUSIONS: This is the first report of the use of fixed and stored tRBCs for HA and HI assays of influenza viruses, highlighting their applicability as a ready-to-use reagent for laboratory diagnosis of influenza.

Virus-Encoded Complement Regulators: Current Status.

Viruses require a host for replication and survival and hence are subjected to host immunological pressures. The complement system, a crucial first response of the host immune system, is effective in targeting viruses and virus-infected cells, and boosting the antiviral innate and acquired immune responses. Thus, the system imposes a strong selection pressure on viruses. Consequently, viruses have evolved multiple countermeasures against host complement. A major mechanism employed by viruses to subvert the complement system is encoding proteins that target complement. Since viruses have limited genome size, most of these proteins are multifunctional in nature. In this review, we provide up to date information on the structure and complement regulatory functions of various viral proteins.

Selection and application of biological safety cabinets in diagnostic and research laboratories with special emphasis on COVID-19.

The ongoing coronavirus disease (COVID-19) pandemic is a global public health emergency. Adherence to biosafety practices is mandatory to protect the user as well as the environment, while handling infectious agents. A biological safety cabinet (BSC) is the most important equipment used in diagnostic and research laboratories in order to safeguard the product, the person, and the environment. The World Health Organization has emphasized the use of validated BSCs in order to ensure quality of the results. There are different classes of BSCs that are used in various work environments based on the need. It is imperative to use appropriate levels of biosafety and types of BSCs in laboratories based on the risk assessment of the pathogen used. During the development of COVID-19 laboratories and training of laboratory staff, we came across several queries about the functions and selection of BSCs and realized that the knowledge about the detailed information on selections and applications of BSCs is scanty. There are several guidelines regarding the biosafety aspects for diagnostic and research laboratories handling infectious pathogens from national and international agencies. However, there is no detailed information on the use of appropriate types of BSCs and their functions in the context of Severe Acute Respiratory Syndrome-Coronavirus 2 (SARS-CoV-2). In view of this, the present paper describes in detail the selection and applications of BSCs, which could be useful for laboratories handling or planning to handle SARS-CoV-2 and suspected samples.

Mapping of functional domains in herpesvirus saimiri complement control protein homolog: complement control protein domain 2 is the smallest structural unit displaying cofactor and decay-accelerating activities.

Herpesvirus saimiri encodes a functional homolog of human regulator-of-complement-activation proteins named CCPH that inactivates complement by accelerating the decay of C3 convertases and by serving as a cofactor in factor I-mediated inactivation of their subunits C3b and C4b. Here, we map the functional domains of CCPH. We demonstrate that short consensus repeat 2 (SCR2) is the minimum domain essential for classical/lectin pathway C3 convertase decay-accelerating activity as well as for factor I cofactor activity for C3b and C4b. Thus, CCPH is the first example wherein a single SCR domain has been shown to display complement regulatory functions.

The imitation game: a viral strategy to subvert the complement system.

Viruses are obligate parasites of cellular hosts and therefore are constantly confronted with the host immune system. Evasion of innate immunity mechanisms by viruses is paramount for the establishment of their infection. The complement system can directly neutralize viruses and also augments adaptive immune responses against them. This system, therefore, is central to host innate immune surveillance, and viruses have evolved a multitude of ways to escape its assault. A major strategy employed by viruses is the molecular mimicry of human complement regulators, namely regulators of complement activation (RCA) proteins and CD59. Herein, we outline up-to-date information on the structure, function and role of viral homologs of the human complement regulators in viral pathogenesis.

Identification of hot spots in the variola virus complement inhibitor (SPICE) for human complement regulation.

Variola virus, the causative agent of smallpox, encodes a soluble complement regulator named SPICE. Previously, SPICE has been shown to be much more potent in inactivating human complement than the vaccinia virus complement control protein (VCP), although they differ only in 11 amino acid residues. In the present study, we have expressed SPICE, VCP, and mutants of VCP by substituting each or more of the 11 non-variant VCP residues with the corresponding residue of SPICE to identify hot spots that impart functional advantage to SPICE over VCP. Our data indicate that (i) SPICE is approximately 90-fold more potent than VCP in inactivating human C3b, and the residues Y98, Y103, K108 and K120 are predominantly responsible for its enhanced activity; (ii) SPICE is 5.4-fold more potent in inactivating human C4b, and residues Y98, Y103, K108, K120 and L193 mainly dictate this increase; (iii) the classical pathway decay-accelerating activity of activity is only twofold higher than that of VCP, and the 11 mutations in SPICE do not significantly affect this activity; (iv) SPICE possesses significantly greater binding ability to human C3b compared to VCP, although its binding to human C4b is lower than that of VCP; (v) residue N144 is largely responsible for the increased binding of SPICE to human C3b; and (vi) the human specificity of SPICE is dictated primarily by residues Y98, Y103, K108, and K120 since these are enough to formulate VCP as potent as SPICE. Together, these results suggest that principally 4 of the 11 residues that differ between SPICE and VCP partake in its enhanced function against human complement.

Direct Saliva Real-time Polymerase Chain Reaction Assay Shows Low Birth Prevalence of Congenital Cytomegalovirus Infection in Urban Western India.

BACKGROUND: Congenital cytomegalovirus (cCMV) infection is the leading infectious cause of mental retardation, developmental delay and sensorineural deafness. Nonprimary infection plays a major role in transmission of this infection in countries with high maternal seroprevalence. Noninvasive sampling and testing is a useful alternative to traditional methods of laboratory detection of congenital CMV infection. The present study was conducted to understand birth prevalence of cCMV infection using molecular techniques, in an urban setting of a developing country with evidence of high maternal seroprevalence. METHODS: Universal newborn screening for cCMV was performed for 750 infants born at a tertiary care center in Western India. Real-time polymerase chain reaction was directly carried out on saliva samples. Follow-up laboratory testing of saliva, urine and blood was performed for neonates identified as positive. Sequential clinical follow-up was offered to the affected infants. RESULTS: A birth prevalence of 0.4% (95% CI: 0.13-1.2) was observed with 3 of 750 babies confirmed to be positive for cCMV infection. All 3 babies were born to seropositive mothers (anti-CMV immunoglobulin G positive). One of the babies detected was symptomatic with sepsis like features. All of them survived and did not develop any sequelae up to 1 year of age. CONCLUSION: The use of direct real-time polymerase chain reaction of saliva samples can be considered as a feasible option for newborn screening of congenital CMV infection in developing countries. Relatively low birth prevalence of cCMV infection was observed in our study, which needs to be corroborated through further studies.

Selection of avian influenza A (H9N2) virus with reduced susceptibility to neuraminidase inhibitors oseltamivir and zanamivir.

Identification of amino-acid substitutions in the neuraminidase (NA) of low-pathogenic avian influenza (AI) H9N2 viruses is important to study the susceptibility to NA inhibitors (NAI). To identify mutations under NAI selective pressure, the virus was serially passaged with increasing levels of either oseltamivir or zanamivir in ovo, and the growth of the viruses in the presence and absence of NAI's compared. Mutations R292 K in the presence of oseltamivir and E119D in presence of zanamivir were observed within passage one and two respectively. The R292 K mutation reduced oseltamivir susceptibility significantly (2,523-fold) and moderately reduced susceptibility to zanamivir. The E119D mutation significantly reduced susceptibility to zanamivir (415-fold) and remained susceptible to oseltamivir. Genetic stability of the mutations assessed by serial passages of the mutant viruses in eggs without drug pressure resulted in the loss of these mutations, making the virus susceptible to both the drugs. Molecular modeling and dynamics simulations revealed that the R292 K mutation disrupted oseltamivir binding similar to other group 2 NAs, while a different mechanism was noted for zanamivir binding for both R292 K and E119D mutations. The study highlights the need for regular susceptibility screening of circulating AI viruses.

A novel I117T substitution in neuraminidase of highly pathogenic avian influenza H5N1 virus conferring reduced susceptibility to oseltamivir and zanamivir.

Occurrence of avian influenza (AI) with Neuraminidase (NA) mutations which confer reduced neuraminidase inhibitor (NAI) susceptibility has remained a cause of concern. The susceptibility to NAIs of 67 highly pathogenic avian influenza H5N1 viruses isolated during 2006-2012 in India was tested in phenotypic fluorescence-based NA inhibition assay, sequence analysis and in ovo. One isolate showed a novel NA I117T amino acid substitution (N2 numbering) and eight isolates showed previously known NAI-resistance marker mutations (I117V, E119D, N294S, total 9/67). The overall incidence of resistant variants was 13.4%. The novel I117T substitution reduced oseltamivir susceptibility by 18.6-fold and zanamivir susceptibility by 11.8-fold, compared to the wild type AI H5N1virus, thus showed cross-resistance to both oseltamivir and zanamivir in NA inhibition assays. However, the other two isolates with I117V substitution were sensitive to both the NAIs. In addition, the comparison of growth of the I117T and I117V variants in presence of NAI's in the in ovo assays exhibited difference in growth levels. The present study reports the natural occurrence of a novel I117T mutation in AI H5N1 virus conferring cross-resistance to oseltamivir and zanamivir highlighting the urgent need of antiviral surveillance of AI viruses.