Comparison of the usefulness of the CACO-2 cell line with standard substrates for isolation of swine influenza A viruses

Influenza A in Wild Boars: Viral Circulation in the Emilia-Romagna Region (Northern Italy) between 2017 and 2022

Simple Summary

Wild boars and feral pigs are underinvestigated hosts for influenza A viruses (IAVs). This study confirmed and evaluated viral circulation in the Emilia-Romagna wild boar population between 2017 and 2022. Samples were collected at post mortems and screened for IAVs; 0.37% of the tested animals provided positive results. Positive samples were subtyped, isolated, and genotyped via full-genome sequencing. The results highlight the co-circulation of the same viral genotypes in overlapping years in both pigs and wild boars in the same geographical area. Considering the role of domestic and wild Sus scrofa species in the IAVs’ ecology, surveillance against these viruses in the wild boar population needs to be implemented.

Abstract

A systematic surveillance against influenza A viruses (IAVs) in the Suidae population is essential, considering their role as IAV mixing vessels. However, the viral circulation in wild Sus scrofa species is poorly investigated in comparison to the knowledge of IAV infection dynamics in domestic pigs. This study investigated the circulation and the genetic diversity of wild boars’ IAVs detected in the Emilia-Romagna region (2017–2022). A total of 4605 lung samples were screened via an M gene real-time RT-PCR for SwIAV; positive samples were subtyped by multiplex RT-PCR, and viral isolation was attempted. Isolated strains (3 out of the 17 positives) were fully sequenced to evaluate viral genotypic diversity. H1N1 was the most frequently detected subtype, with identification of H1pdm09N1 and H1avN1. Whole-genome phylogenetic analysis revealed SwIAVs belonging to different genotypes, with different genetic combinations, and highlighted the simultaneous circulation of the same genotypes in both pigs and wild boars, supporting the hypothesis of SwIAV spillover events at the wildlife–livestock interface. This study represents an update on the wild boar SwIAV Italian situation, and the strains’ complete genome analysis showed an evolving and interesting situation that deserves further investigation.

CRISPR-Cas9 mediated knockout of AnxA6 gene enhances influenza A virus replication in low-permissive HEK293FT cell line

Using cell cultures of human origin for the propagation of influenza virus is an attractive way to preserve its glycosylation profile and antigenic properties, which is essential in influenza surveillance and vaccine production. However, only few cell lines are highly permissive to influenza virus, and none of them are of human origin. The barrier might be associated with host restriction factors inhibiting influenza growth, such as AnxA6 protein counteracting the process of influenza virion packaging. In the presented work we explore the CRISPR-Cas9 mediated knockout of ANXA6 gene as a way to overcome the host restriction barrier and increase the susceptibility of human cell line to influenza infection. By CRISPR-Cas9 genome editing we modified HEK293FT cells and obtained several clones defective in the ANXA6 gene. The replication of the influenza A virus in original HEK293FT cells and the HEK293FT-ANXA6^-/- mutant cells was compared in growth curve experiments. By combination of methods including TCID assay and flow cytometry we showed that accumulation of influenza A virus in the mutant HEK293FT-ANXA6^-/- cells significantly exceeded the virus titer in the original HEK293FT cells.

Genetic Variability among Swine Influenza Viruses in Italy: Data Analysis of the Period 2017-2020

Swine play an important role in the ecology of influenza A viruses (IAVs), acting as mixing vessels. Swine (sw) IAVs of H1N1 (including H1N1pdm09), H3N2, and H1N2 subtypes are enzootic in pigs globally, with different geographic distributions. This study investigated the genetic diversity of swIAVs detected during passive surveillance of pig farms in Northern Italy between 2017 and 2020. A total of 672 samples, IAV-positive according to RT-PCR, were subtyped by multiplex RT-PCR. A selection of strains was fully sequenced. High genotypic diversity was detected among the H1N1 and H1N2 strains, while the H3N2 strains showed a stable genetic pattern. The hemagglutinin of the H1Nx swIAVs belonged to HA-1A, HA-1B, and HA-1C lineages. Increasing variability was found in HA-1C strains with the circulation of HA-1C.2, HA-1C.2.1 and HA-1C.2.2 sublineages. Amino acid deletions in the HA-1C receptor binding site were observed and antigenic drift was confirmed. HA-1B strains were mostly represented by the Δ146-147 Italian lineage HA-1B.1.2.2, in combination with the 1990s human-derived NA gene. One antigenic variant cluster in HA-1A strains was identified in 2020. SwIAV circulation in pigs must be monitored continuously since the IAVs’ evolution could generate strains with zoonotic potential.

The epidemiology of swine influenza

Globally swine influenza is one of the most important diseases of the pig industry, with various subtypes of swine influenza virus co-circulating in the field. Swine influenza can not only cause large economic losses for the pig industry but can also lead to epidemics or pandemics in the human population. We provide an overview of the pathogenic characteristics of the disease, diagnosis, risk factors for the occurrence on pig farms, impact on pigs and humans and methods to control it. This review is designed to promote understanding of the epidemiology of swine influenza which will benefit the control of the disease in both pigs and humans.

CACO-2 cells: A continuous cell line with sensitive and broad-spectrum utility for respiratory virus culture

BACKGROUND

Primary rhesus monkey kidney cells (RhMK) can be used for the detection of respiratory viruses, including influenza and parainfluenza. The human colon adeno-carcinoma cell line, CACO-2, has been previously used for the growth of multiple influenza viruses, including seasonal, novel and avian lineages.

OBJECTIVE

We compared CACO-2, Madin-Darby Canine Kidney (MDCK), and RhMK cells for the isolation of viruses from patients presenting with influenza like-illness (ILI).

STUDY DESIGN

Nasopharyngeal specimens from patients with ILI in primary care settings were processed for conventional viral culture in MDCK, RhMK, and CACO-2. Cells were examined microscopically for cytopathic effect (CPE) and confirmatory testing included immunofluorescent antigen (IFA) detection and real-time RT-PCR. Additionally, 16 specimens positive for respiratory syncytial virus (RSV) by PCR were inoculated on CACO-2 cells. Statistical analysis was done using Chi-square test with IBM Statistical Program.

RESULTS

Of 1031 respiratory specimens inoculated, viruses were isolated and confirmed from 331 (32.1 %) in MDCK cells, 304 (29.5 %) in RhMk cells, and 433 (42.0 %) in CACO-2 cells. These included influenza A/(H1N1)pdm09, influenza A(H3N2), influenza B, parainfluenza virus (PIV) types 1, 2, and 3, human coronavirus 229E (CoV-229E), human adenovirus (HAdV), herpes simplex virus 1 (HSV 1), and enterovirus (EV). Influenza A viruses grew best in the CACO-2 cell line. Time to observation of CPE was similar for all three cell types but unlike RhMK and MDCK cells, virus-specific morphological changes were indistinguishable in CACO-2 cells. None of the 16 specimens positive for RSV by PCR grew on CACO-2 cells.

CONCLUSIONS

The overall respiratory virus culture isolation rate in CACO-2 cells was significantly higher than that in RhMK or MDCK cells (p < 0.05). CACO-2 cells also supported the growth of some viruses that did not grow in either RhMK or MDCK cells. Except for RSV, CACO-2 cells provide a worthwhile addition to culture algorithms for respiratory specimens.

Isolation of Swine Influenza A Virus in Cell Cultures and Embryonated Chicken Eggs

Influenza virus isolation is a procedure to obtain a live and infectious virus that can be used for antigenic characterization, pathogenesis investigation, vaccine production, and so on. Embryonated chicken egg inoculation is traditionally considered the "gold standard" method for influenza virus isolation and propagation. However, many primary cells and continuous cell lines have also been examined or developed for influenza virus isolation and replication. Specifically, influenza A virus in swine (IAV-S) isolation and propagation has been attempted and compared in embryonated chicken eggs, some primary porcine cells, and a number of continuous cell lines. Currently, Madin-Darby canine kidney (MDCK) cells remain the most commonly used cell line for the isolation, propagation, and titration of IAV-S. Virus isolation in embryonated chicken eggs or in different cell lines offers alternative approaches when IAV-S isolation in MDCK cells is unsuccessful. Optimal specimens for IAV-S isolation includes nasal swabs, nasopharyngeal swabs, oral fluids, bronchoalveolar lavage, lung tissues, and so on. In this chapter, we describe the procedures of sample processing, IAV-S isolation in MDCK cells and in embryonated chicken eggs, as well as the methods used for confirming the virus isolation results.

Functional evaluation for adequacy of MDCK-lineage cells in influenza research

Objective

Influenza is an acute respiratory disease caused by the influenza virus which circulates annually in populations of different species. Madin-Darby Canine Kidney (MDCK) is the most widely utilized cell-line for conducting influenza research. However, the infectivity of various influenza strains in MDCK cells is not equivalent and the productivity of viral propagation is also limited.

Results

We tested the functional adequacy of two MDCK-lineage cell lines, conventional MDCK and MDCK/London, were evaluated by assessing their infectivity of different influenza viral strains with focus forming assays and the cellular toxicity caused by influenza infections by lactate dehydrogenase assay. Moreover, the sensitivity of cells in the presence of the antiviral agent ribavirin was assessed by MTT assay. Our results showed that MDCK/London cells efficiently propagate virus across all influenza viruses tested, are comparable to the utility of Mv1Lu cells, and are superior to conventional MDCK cells in replicating virus as indicated by an increase in virus of three to four logs, particularly in H3N2 infection. Also, the MDCK/London cells were more sensitive to the presence of antiviral drug than conventional MDCK cells. In conclusion, MDCK/London cell line could be a better platform for influenza studies and vaccine development.

Genetic analysis of human and swine influenza A viruses isolated in Northern Italy during 2010-2015

Influenza A virus (IAV) infection in swine plays an important role in the ecology of influenza viruses. The emergence of new IAVs comes through different mechanisms, with the genetic reassortment of genes between influenza viruses, also originating from different species, being common. We performed a genetic analysis on 179 IAV isolates from humans (n. 75) and pigs (n. 104) collected in Northern Italy between 2010 and 2015, to monitor the genetic exchange between human and swine IAVs. No cases of human infection with swine strains were noticed, but direct infections of swine with H1N1pdm09 strains were detected. Moreover, we pointed out a continuous circulation of H1N1pdm09 strains in swine populations evidenced by the introduction of internal genes of this subtype. These events contribute to generating new viral variants-possibly endowed with pandemic potential-and emphasize the importance of continuous surveillance at both animal and human level.

Development and evaluation of a new Real-Time RT-PCR assay for detection of proposed influenza D virus

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Development of a new Real-Time RT-PCR for detection of IDV.

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The new Real-Time RT-PCR showed high sensitivity and specificity.

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The new Real-Time RT-PCR can be used for diagnostics and as a confirmatory test.

The occurrence of virus belonging to the putative genus Influenzavirus D, has been demonstrated all-around the world arousing interest within the scientific community. Most of the published virological surveys are based on the first described Real-Time PCR method, designed on the PB1 gene of the first isolate. The necessity of extending investigation to different animal species and geographic areas, requires a continuous update of molecular tests, considering newly sequenced strains. Moreover, the availability of an alternative assay, is essential either to confirm data, or for ensuring the detection of the widest number of strains. A new Real-Time PCR, specific for influenza D virus (IDV), was developed and evaluated. The target sequences of primers and probe are highly conserved among IDV strains currently known. The specificity of the method was demonstrated in silico by BLAST, and in vitro with a huge panel of common swine and bovine respiratory pathogens. The analytical sensitivity of the Real-Time PCR was estimated through synthetic RNA molecules and the limit of detection was about 20 copies/μL. The assay was assessed in field and proved to be a valuable tool for the detection of IDV strains.

Protein mutations following adaptation of avian influenza viruses in different biological systems

Traditionally, embryonated chicken eggs (ECE) are considered the gold standard for Influenza virus isolation and vaccine production. Nowadays, different biological systems have been improved and performed, in order to evaluate a feasible alternative to ECE. In fact, in a previous study, mammalian and avian cell cultures were successfully used for avian influenza viruses primary isolation from target tissues and virus propagation. This research is focused on the investigation of adaptive mutations that occur after influenza A virus amplification in ECE and cell cultures. The results of the study shows that avian influenza viruses after multiple passages in different biological systems undergo mutations, in particular, the largest number of amino acid substitutions occurred in all biological substrates in the hemagglutinin.

Prevalence of gastrointestinal symptoms in patients with influenza, clinical significance, and pathophysiology of human influenza viruses in faecal samples: what do we know?

This review provides for the first time an assessment of the current understanding about the occurrence and the clinical significance of gastrointestinal (GI) symptoms in influenza patients, and their correlation with the presence of human influenza viruses in stools of patients with confirmed influenza virus infection. Studies exploring how human influenza viruses spread to the patient’s GI tract after a primary respiratory infection have been summarized. We conducted a systematic search of published peer-reviewed literature up to June 2015 with regard to the above-mentioned aspects, focusing on human influenza viruses (A(H1N1), A(H1N1)pdm09, A(H3N2), and B). Forty-four studies were included in this systematic review and meta-analysis. The pooled prevalence of any digestive symptoms ranged from 30.9 % (95 % CI, 9.8 to 57.5; I² = 97.5 %) for A(H1N1)pdm09 to 2.8 % (95 % CI, 0.6 to 6.5; I² = 75.4 %) for A(H1N1). The pooled prevalence of influenza viruses in stool was 20.6 % (95 % CI, 8.9 to 35.5; I² = 96.8 %), but their correlation with GI symptoms has rarely been explored. The presence of viral RNA in stools because of haematogenous dissemination to organs via infected lymphocytes is likely, but the potential to cause direct intestinal infection and faecal–oral transmission warrants further investigation. This review highlights the gaps in our knowledge, and the high degree of uncertainty about the prevalence and significance of GI symptoms in patients with influenza and their correlation with viral RNA positivity in stool because of the high level of heterogeneity among studies.

Detection and Isolation of Swine Influenza A Virus in Spiked Oral Fluid and Samples from Individually Housed, Experimentally Infected Pigs: Potential Role of Porcine Oral Fluid in Active Influenza A Virus Surveillance in Swine

Background

The lack of seasonality of swine influenza A virus (swIAV) in combination with the capacity of swine to harbor a large number of co-circulating IAV lineages, resulting in the risk for the emergence of influenza viruses with pandemic potential, stress the importance of swIAV surveillance. To date, active surveillance of swIAV worldwide is barely done because of the short detection period in nasal swab samples. Therefore, more sensitive diagnostic methods to monitor circulating virus strains are requisite.

Methods

qRT-PCR and virus isolations were performed on oral fluid and nasal swabs collected from individually housed pigs that were infected sequentially with H1N1 and H3N2 swIAV strains. The same methods were also applied to oral fluid samples spiked with H1N1 to study the influence of conservation time and temperature on swIAV infectivity and detectability in porcine oral fluid.

Results

All swIAV infected animals were found qRT-PCR positive in both nasal swabs and oral fluid. However, swIAV could be detected for a longer period in oral fluid than in nasal swabs. Despite the high detectability of swIAV in oral fluid, virus isolation from oral fluid collected from infected pigs was rare. These results are supported by laboratory studies showing that the PCR detectability of swIAV remains unaltered during a 24 h incubation period in oral fluid, while swIAV infectivity drops dramatically immediately upon contact with oral fluid (3 log titer reduction) and gets lost after 24 h conservation in oral fluid at ambient temperature.

Conclusions

Our data indicate that porcine oral fluid has the potential to replace nasal swabs for molecular diagnostic purposes. The difficulty to isolate swIAV from oral fluid could pose a drawback for its use in active surveillance programs.

Isolation of swine influenza virus in cell cultures and embryonated chicken eggs

Influenza virus isolation is a procedure to obtain a live and infectious virus that can be used for antigenic characterization, pathogenesis investigation, and vaccine production. Embryonated chicken egg inoculation is traditionally considered the "gold standard" method for influenza virus isolation and propagation. However, many primary cells and continuous cell lines have also been examined or developed for influenza virus isolation and replication. Specifically, swine influenza virus (SIV) isolation and propagation have been attempted and compared in embryonated chicken eggs, some primary porcine cells, and a number of continuous cell lines. Currently Madin-Darby canine kidney (MDCK) cells remain the most commonly used cell line for isolation, propagation, and titration of SIV. Virus isolation in embryonated chicken eggs or in different cell lines offers alternative approaches when SIV isolation in MDCK cells is unsuccessful. Nasal swabs, lung tissues, and oral fluids are three major specimen types for SIV isolation. In this chapter, we describe the procedures of sample processing, SIV isolation in MDCK cells and in embryonated chicken eggs, as well as methods used for confirming the virus isolation results.

European surveillance network for influenza in pigs: surveillance programs, diagnostic tools and Swine influenza virus subtypes identified in 14 European countries from 2010 to 2013

Swine influenza causes concern for global veterinary and public health officials. In continuing two previous networks that initiated the surveillance of swine influenza viruses (SIVs) circulating in European pigs between 2001 and 2008, a third European Surveillance Network for Influenza in Pigs (ESNIP3, 2010–2013) aimed to expand widely the knowledge of the epidemiology of European SIVs. ESNIP3 stimulated programs of harmonized SIV surveillance in European countries and supported the coordination of appropriate diagnostic tools and subtyping methods. Thus, an extensive virological monitoring, mainly conducted through passive surveillance programs, resulted in the examination of more than 9 000 herds in 17 countries. Influenza A viruses were detected in 31% of herds examined from which 1887 viruses were preliminary characterized. The dominating subtypes were the three European enzootic SIVs: avian-like swine H1N1 (53.6%), human-like reassortant swine H1N2 (13%) and human-like reassortant swine H3N2 (9.1%), as well as pandemic A/H1N1 2009 (H1N1pdm) virus (10.3%). Viruses from these four lineages co-circulated in several countries but with very different relative levels of incidence. For instance, the H3N2 subtype was not detected at all in some geographic areas whereas it was still prevalent in other parts of Europe. Interestingly, H3N2-free areas were those that exhibited highest frequencies of circulating H1N2 viruses. H1N1pdm viruses were isolated at an increasing incidence in some countries from 2010 to 2013, indicating that this subtype has become established in the European pig population. Finally, 13.9% of the viruses represented reassortants between these four lineages, especially between previous enzootic SIVs and H1N1pdm. These novel viruses were detected at the same time in several countries, with increasing prevalence. Some of them might become established in pig herds, causing implications for zoonotic infections.

Epidemiological survey of swine influenza A virus in the wild boar population of two Italian provinces

OBJECTIVES

An epidemiological survey was carried out in order to obtain a better understanding of the role of wild boars in the epidemiology of the influenza virus.

DESIGN

The samples were submitted to Real-Time PCR testing for gene M of the swine influenza virus (SIV), and virus isolation was performed from the positive PCR samples. Genome sequence analysis was performed on the isolates. Additionally, 1,977 boar sera samples were analyzed using ELISA and hemoagglutination inhibition.

SETTING

Over recent years, the wild boar population has greatly increased in Italy, including in areas of high-density industrial pig farming, where the influenza virus is widespread. From July to December 2012, wild boar lung samples were collected in the Parma and Piacenza area, in the Emilia Romagna region.

SAMPLE

354 wild boar lung samples were collected.

MAIN OUTCOME MEASURES

Wild-boar influenza A virus infection should be studied more broadly in order to obtain a better understanding of the epidemiological role played by this species.

RESULTS

Three SIV strains were isolated out of 12 samples that resulted positive using PCR analysis and they were identified as avian-like SIV subtype H1N1. Phylogenetic analysis of the sequences obtained from isolate A/wild boar/291320/2012 showed that it clustered with recent Italian avian-like H1N1 SIVs isolated from domestic pigs. Sixty-eight sera samples showed a positive titer to the isolate A/wild boar/291320/2012.

CONCLUSIONS

This study suggests that SIV actively circulates in the wild boar population in the investigated. area.

Use of the human colorectal adenocarcinoma (Caco-2) cell line for isolating respiratory viruses from nasopharyngeal aspirates

The human colorectal adenocarcinoma‐derived Caco‐2 cell line was evaluated as a means isolating common respiratory viruses from nasopharyngeal aspirates for the diagnosis of respiratory diseases. One hundred eighty‐nine direct immunofluorescence positive nasopharyngeal aspirates obtained from patients with various viral respiratory diseases were cultured in the presence of Caco‐2 cells or the following conventional cell lines: LLC‐MK2, MDCK, HEp‐2, and A549. Caco‐2 cell cultures effectively propagated the majority (84%) of the viruses present in nasopharyngeal aspirate samples compared with any positive cultures obtained using the panel cells (78%) or individual cell line MDCK (38%), HEp‐2 (21%), LLC‐MK2 (27%), or A549 (37%) cell lines. The differences against individual cell line were statistically significant (P = < 0.000001). Culture in Caco‐2 cells resulted in the isolation of 85% (36/42) of viruses which were not cultivated in conventional cell lines. By contrast, 80% (24/30) of viruses not cultivated in Caco‐2 cells were isolated using the conventional panel. The findings indicated that Caco‐2 cells were sensitive to a wide range of viruses and can be used to culture a broad range of respiratory viruses. J. Med. Virol. 85:874–879, 2013. © 2013 Wiley Periodicals, Inc.

Comparison of different cell substrates on the measurement of human influenza virus neutralizing antibodies

Eight cell lines were systematically compared for their permissivity to primary infection, replication, and spread of seven human influenza viruses. Cell lines were of human origin (Caco-2, A549, HEp-2, and NCI-H292), monkey (Vero, LLC-MK2), mink (Mv1 Lu), and canine (MDCK). The influenza viruses included seasonal types and subtypes and a pandemic virus. The MDCK, Caco-2, and Mv1 Lu cells were subsequently compared for their capacity to report neutralization titers at day one, three and six post-infection. A gradient of sensitivity to primary infection across the eight cell lines was observed. Relative to MDCK cells, Mv1 Lu reported higher titers and the remaining six cell lines reported lower titers. The replication and spread of the seven influenza viruses in the eight cell substrates was determined using hemagglutinin expression, cytopathic effect, and neuraminidase activity. Virus growth was generally concordant with primary infection, with a gradient in virus replication and spread. However, Mv1 Lu cells poorly supported virus growth, despite a higher sensitivity to primary infection. Comparison of MDCK, Caco-2, and Mv1 Lu in neutralization assays using defined animal antiserum confirmed MDCK cells as the preferred cell substrate for influenza virus testing. The results observed for neutralization at one day post-infection showed MDCK cells were similar (<1 log₂ lower) or superior (>1 log₂ higher) for all seven viruses. Relative to Caco-2 and Mv1 Lu cells, MDCK generally reported the highest titers at three and six days post-infection for the type A viruses and lower titers for the type B viruses and the pandemic H9N2 virus. The reduction in B virus titer was attributed to the complete growth of type B viruses in MDCK cells before day three post-infection, resulting in the systematic underestimation of neutralization titers. This phenomenon was also observed with Caco-2 cells.

Comparative effectiveness of isolation techniques for contemporary Influenza A virus strains circulating in exhibition swine

The current study sought to compare the effectiveness of 2 virus isolation methods for the recovery of contemporary Influenza A virus (FLUAV) strains circulating in swine at agricultural exhibitions. Following the emergence of the influenza A (H1N1)pdm09 virus, increased surveillance of FLUAV strains among swine was recommended for early detection of emerging strains that threaten animal and human health. The increase in genetic drift and genomic reassortment among FLUAV strains infecting swine since 1998 necessitates that detection protocols be periodically validated for contemporary FLUAV strains. During 2009, nasal swabs were collected from 221 clinically healthy pigs at 12 agricultural exhibitions in Ohio. Nasal swabs were tested in parallel for the presence of FLUAV strains using 3 methodologies: 2 passages through Madin-Darby canine kidney (MDCK) cells adapted to serum-free medium (SFM), 2 passages through embryonated chicken eggs (ECEs), and real-time reverse transcription polymerase chain reaction (real-time RT-PCR). Of the 221 samples, 40 (18.1%) were positive for FLUAV recovery in MDCK cell culture and 13 (5.9%) were positive in ECEs (P = 0.015). All samples positive in ECEs were also positive in MDCK cell culture. MDCK cell culture virus isolation results were in perfect agreement with results of the real-time RT-PCR. Hemagglutinin and neuraminidase combinations of the recovered isolates were H1N2 and H3N2, which were consistent with FLUAV strains circulating in U.S. pigs. Effectiveness and cost savings justify the use of SFM-adapted MDCK cell culture over ECEs for the recovery of contemporary FLUAV strains from exhibition swine.

Isolation of the pandemic (H1N1) 2009 virus and its reassortant with an H3N2 swine influenza virus from healthy weaning pigs in Thailand in 2011

A total of 300 nasal swabs were collected from 5 pig farms in two provinces in the Eastern part of Thailand in February 2011 and were subjected to viral isolation of influenza A viruses. Two H3N2 and 6 H1N1 influenza A viruses were isolated from swabs collected from clinically healthy weaning pigs on farms in Chonburi and Chachoengsao provinces, respectively. The H3N2 isolates consisted of the hemagglutinin (HA) and neuraminidase (NA) genes closely related to Thai SIVs and derived from a cluster of human seasonal H3N2 strains circulating around 1996-1997. The remaining gene segments of the isolates originated from the Pandemic (H1N1) 2009 (A (H1N1) pdm09) virus. Antigenicity of the H3N2 isolates was distinguishable from a human seasonal vaccine strain in the 1996-1998 seasons that represented antigenicity of the seasonal strains around 1996-1998. Nasal swabs from a Chachoengsao farm yielded A (H1N1) pdm09 viruses in chicken embryonated eggs and MDCK cells. A (H1N1) pdm09 viruses isolated in this study grew poorly in MDCK cells. Deduced amino acid sequences of the HA1 region of the HA protein of egg isolated viruses were identical to the sequences directly amplified from original swab samples. Our result demonstrated that the A (H1N1) pdm09 virus has been established in the Thai pig population and this has resulted in genetic reassortment with Thai SIV that previously circulated among pigs.

Susceptibility of different cell lines to Avian and Swine Influenza viruses

Influenza outbreaks are widespread in swine and avian populations. Disease control is jeopardized by the extreme antigenic variability of virus strains. Primary isolation of Influenza virus is performed using embryonated chicken eggs (ECE), but alternatives to ECE are badly needed. Although various cultured cells have been used for propagating Influenza A viruses, few types of cells can efficiently support virus replication. One of the most commonly cell lines used in order to isolate Influenza A virus, is represented by the Madin Darby Canine Kidney (MDCK) cell line, but cells derived from primary swine organs (kidney, testicle, lung and trachea) can also be employed. The aim of this study was the evaluation of NSK, MDCK, UMNSAH/DF1 cell lines suitability, compared to ECE for isolation and propagation of Avian and Swine virus subtypes. The results indicated both NSK and MDCK could provide an appropriate substrate for cultivating either Avian (AIV) or Swine (SIV) Influenza virus strains, especially for high pathogenicity Avian Influenza ones. Furthermore, NSK appeared more susceptible than MDCK cells for primary isolation of AIV. In contrast, UMNSAH/DF1 cell line seemed to be less permissive to support Avian virus growth. Furthermore, no SIV replication was detected except for one subtype. Additionally, the results of this study indicated that not all virus strains seemed to adapt with the same efficiency to the different cell lines. On the contrary, chicken embryos were shown to be the most suitable biological system for AIV isolation.

Multiplex RT-PCR assay for differentiating European swine influenza virus subtypes H1N1, H1N2 and H3N2

In Europe, three major swine influenza viral (SIV) subtypes (H1N1, H1N2 and H3N2) have been isolated in pigs. Developing a test that is able to detect and identify the subtype of the circulating strain rapidly during an outbreak of respiratory disease in the pig population is of essential importance. This study describes two multiplex RT-PCRs which distinguish the haemagglutinin (HA) gene and the neuraminidase (NA) gene of the three major subtypes of SIV circulating in Europe. The HA PCR was able to identify the lineage (avian or human) of the HA of H1 subtypes. The analytical sensitivity of the test, considered to be unique, was assessed using three reference viruses. The detection limit corresponded to 1×10(-1) TCID(50)/200μl for avian-like H1N1, 1×10(0) TCID(50)/200μl for human-like H1N2 and 1×10(1) TCID(50)/200μl for H3N2 SIV. The multiplex RT-PCR was first carried out on a collection of 70 isolated viruses showing 100% specificity and then on clinical samples, from which viruses had previously been isolated, resulting in an 89% positive specificity of the viral subtype. Finally, the test was able to identify the viral subtype correctly in 56% of influenza A positive samples, from which SIV had not been isolated previously. It was also possible to identify mixed viral infections and the circulation of a reassortant strain before performing genomic studies.