This work is supported in part NIH grants R01 A1064826-01, U19 AI062627-01, NO1-HHSN26600500032C (to S.M.). We thank our laboratory members for discussion and technical help, Tina Heil for the critical review of the manuscript. We would like to thank David Bina, Milwaukee Health Department Laboratory for virus culture and PCR.

<ol>
	<li>Hirst, G. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+agglutination+of+red+cells+by+allantoic+fluid+of+chick+embryos+infected+with+influenza+virus.">The agglutination of red cells by allantoic fluid of chick embryos infected with influenza virus.</a> Science. 94, 22-23 (1941).</li><li>Jonsson, N., Gullberg, M., Lindberg, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Real-time+polymerase+chain+reaction+as+a+rapid+and+efficient+alternative+to+estimation+of+picornavirus+titers+by+tissue+culture+infectious+dose+50%+or+plaque+forming+units.">Real-time polymerase chain reaction as a rapid and efficient alternative to estimation of picornavirus titers by tissue culture infectious dose 50% or plaque forming units.</a> Microbiol. Immunol. 53, 149-154 (2009).</li><li>Kalter, S. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hemagglutinating+Behavior+of+Mouse+and+Egg-adapted+Type+A+(PR8)+Influenza+Virus.">Hemagglutinating Behavior of Mouse and Egg-adapted Type A (PR8) Influenza Virus.</a> Science. 110, 184-184 (1949).</li><li>Dulbecco, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Production+of+Plaques+in+Monolayer+Tissue+Cultures+by+Single+Particles+of+an+Animal+Virus.">Production of Plaques in Monolayer Tissue Cultures by Single Particles of an Animal Virus.</a> Proc. Natl. Acad. Sci. U. S. A. 38, 747-752 (1952).</li><li>Deyde, V. M., Nguyen, T., Bright, R. A., Balish, A., Shu, B., Lindstrom, S., Klimov, A. I., Gubareva, L. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detection+of+molecular+markers+of+antiviral+resistance+in+influenza+A+(H5N1)+viruses+using+a+pyrosequencing+method.">Detection of molecular markers of antiviral resistance in influenza A (H5N1) viruses using a pyrosequencing method.</a> Antimicrob. Agents Chemother. 53, 1039-1047 (2009).</li><li>Jonsson, N., Gullberg, M., Lindberg, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Real-time+polymerase+chain+reaction+as+a+rapid+and+efficient+alternative+to+estimation+of+picornavirus+titers+by+tissue+culture+infectious+dose+50%+or+plaque+forming+units.">Real-time polymerase chain reaction as a rapid and efficient alternative to estimation of picornavirus titers by tissue culture infectious dose 50% or plaque forming units.</a> Microbiol. Immunol. 53, 149-154 (2009).</li><li>Rahman, M., Kieke, B. A., Vandermause, M. F., Mitchell, P. D., Greenlee, R. T., Belongia, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Performance+of+Directigen+flu+A+B+enzyme+immunoassay+and+direct+fluorescent+assay+for+detection+of+influenza+infection+during+the+2004-2005+season.">Performance of Directigen flu A+B enzyme immunoassay and direct fluorescent assay for detection of influenza infection during the 2004-2005 season.</a> Diagnostic Microbiology and Infectious Disease. 58, 413-418 (2007).</li><li>Landry, M. L., Ferguson, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Suboptimal+detection+of+influenza+virus+in+adults+by+the+Directigen+Flu+A+B+enzyme+immunoassay+and+correlation+of+results+with+the+number+of+antigen-positive+cells+detected+by+cytospin+immunofluorescence.">Suboptimal detection of influenza virus in adults by the Directigen Flu A+B enzyme immunoassay and correlation of results with the number of antigen-positive cells detected by cytospin immunofluorescence.</a> J. Clin. Microbiol. 41, 3407-3409 (2003).</li><li>Herrmann, B., Larsson, C., Zweygberg, B. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+detection+and+typing+of+influenza+viruses+A+and+B+by+a+nested+reverse+transcription-PCR:+comparison+to+virus+isolation+and+antigen+detection+by+immunofluorescence+and+optical+immunoassay+(FLU+OIA).">Simultaneous detection and typing of influenza viruses A and B by a nested reverse transcription-PCR: comparison to virus isolation and antigen detection by immunofluorescence and optical immunoassay (FLU OIA).</a> J. Clin. Microbiol. 39, 134-138 (2001).</li><li>Reed, L. J., Muench, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+method+of+estimating+fifty+percent+endpoints.">A simple method of estimating fifty percent endpoints.</a> Am. J. Epidemiol. 27, 493-497 (1938).</li><li>Doerr, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+proteins:+into+the+infrared.">Fluorescent proteins: into the infrared.</a> Nat. Meth. 6, 482-483 (2009).</li><li>Shu, B., Wu, K. H., Emery, S., Villanueva, J., Johnson, R., Guthrie, E., Berman, L., Warnes, C., Barnes, N., Klimov, A., Lindstrom, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+and+performance+of+the+CDC+real-time+reverse+transcriptase+PCR+swine+flu+panel+for+detection+of+2009+A+(H1N1)+pandemic+influenza+virus.">Design and performance of the CDC real-time reverse transcriptase PCR swine flu panel for detection of 2009 A (H1N1) pandemic influenza virus.</a> J. Clin. Microbiol. 49, 2614-2619 (2011).</li></ol>

We have nothing to disclose.

The recent epidemic outbreak of avian influenza in Southeast Asia and a global fear of the swine flu pandemic impose enormous concerns to public health and safety. Critical focus has been dedicated in generating vaccines for existing and newer strains of influenza virus. Availability of rapid high-throughput technologies for precise detection and accurate viral titer calculations will tremendously improve treatment. The most commonly used techniques employed to calculate virus titer include plaque forming and influenza hemagglutination assays. The plaque forming assay was first developed to estimate bacteriophage titers and was adopted by Renato Dulbecco to calculate animal viral titers 4. To perform this assay, 10-fold dilutions of influenza stock or animal specimens such as BAL fluid are prepared and 0.1 ml aliquots are inoculated onto the monolayer of MDCK cells in 6-well plates. The virus is allowed to adsorb onto the MDCK cells followed by the addition of a nutrient medium and agarose. During the incubation, the original infected cells release viral progeny that spread only to the neighboring cells. The cytopathogenic effect of the influenza viral infection produces a circular zone of infected cells called a plaque. Each plaque is presumably formed after infection of a single cell with a single virus particle followed by replication of virus. Contrast between the living cells and the plaques can be enhanced by dyes such as crystal violet. A major drawback of this assay is lack of reproducibility and huge variations within experiments. Another assay used to determine the influenza viral titer is the hemagglutination assay. The hemagglutinin protein present on the surface of the influenza virus efficiently binds to N-acetylneuraminic acid-containing proteins on mammalian and avian red blood cells 1. This interaction between the influenza virus and the erythrocytes leads to agglutination in the form of a lattice. The level of agglutination is used to estimate the titer of the influenza virus in test specimens. Erythrocyte agglutination assay is used only to determine the titration of a known virus and cannot be used for strain identification purposes. Since this assay does not differentiate between the live and the dead viruses, it is difficult to obtain a precise calculation of viral titers.
Current clinical diagnoses of influenza infections are based on serologic testing, polymerase chain reaction, direct specimen immunofluorescence and cell culture 1,6. The new method described here also has clinical and laboratory diagnostic potential. Influenza detection kits Directigen FLU-A (BD Biosciences, San Jose, CA) and BinaxNow (Binax, Inc., Scarborough, ME) use immunochromatography assay to detect viral antigen such as nucleoprotein 7. Using these kits, detection of virus can be achieved within 15 min; however, all negative samples have to be further screened by the cell culture method. Various studies have also reported low sensitivity of these kits, particularly, when infection was mild or low 8. In our method, we consistently detect as low as 100 PFU of virus. This suggests our technique is useful in detecting H1N1 virus in clinical samples, even when the infection is mild. A fluorescence-based method to detect viral antigens has been reported, where either nasopharyngeal aspirate specimens were directly analyzed or were inoculated onto a monolayer of susceptible cells for virus multiplication and subsequent analyses 9. However, these methods are limited for diagnostic purposes and are not suitable for virus titer calculations. Q-PCR helps to identify the presence of viral RNA and does not estimate the infectivity of live viruses. Compared to these assays, IR dye-based assay system will help in the detection and viral titer enumeration in clinical and laboratory samples. In case of influenza outbreak, it is critical to diagnose thousands of samples in a short time period. Our method based on a 384-well plate and IR scanner can scan 6-plates at a time (&gt;2,000 samples), therefore offering a greater advantage over other direct fluorescent methods. Feasibility of rapid processing of thousands of clinical samples could reduce test variability, length of assay time and costs. The use of an M2-specific antibody offers the advantage of being independent of strain differences in H and N proteins. The M2-protein is relatively conserved in most influenza strains infecting humans. If antibodies specific to circulating stains are combined with our system one can measure both the titer of virus and identify the strain. However, since M2 is the target for the Amantadine-like drugs, mutants can arise that might change the binding site for the mAb used here. This represents a potential limitation for this system in individuals who are being treated by these drugs.
Multiple assays are used to enumerate influenza titers in test samples. To calculate virus titer, 50% tissue culture infectious dose (TCID50) and egg allantoic fluid-based assays are widely used 1,10. However, requirements of multiple days make these methods less reliable. Further, in these methods calculations based on the 50% change in the number of plaques provide theoretical but not accurate viral titrations. Plaque forming assays can be performed within 96 hours; however, lack of reproducibility is a major concern in viral titer calculations. The present technique described here has several distinct advantages. First, it is a highly reproducible technique with consistent outcomes. Second, viral titer calculations are based on simple quantification of fluorescence intensities that are compared against defined standard curves. Third, two or more primary antibodies can be used to diagnose multiple serotypes in a given sample. Also, IR dye-conjugated antibodies have minimal autofluorescence and have been used for cell imaging 11. UV or visual radiation (300-600 nM) results in high cellular autofluorescence due to the presence of high quantum yielding endogenous fluorophores. These include aromatic amino acids, lipo-pigments, pyridinic nucleotides (NADPH), elastin, collagen and flavin coenzymes. This intrinsic property of cells makes it difficult to utilize these sources of radiation as probes to quantify the expression of specific proteins. In contrast, near-IR dyes excite and emit between 670-1000 nm. Many host cellular molecules and polyaromatic hydrocarbons do not excite at this wavelength and due to reduced light scattering, emit extremely low background fluorescence. Further, the window between the background and specific detection is vastly improved due to a high extinction coefficient of the near-IR fluorophores. Photostability, superior signal-to-noise ratio, is extremely relevant in the quantification of viral titers. Use of microfluidic chambers will automate the screening process through robotic controls, and could allow us to test highly contagious clinical samples with ease. Thus, the utilization of near-IR dyes in these methods is ideal and highly reliable to enumerate viral titers in tissue samples.

<table border="1">
 <tbody>
 <tr>
 <td>Name of the reagent</td>
 <td>Company</td>
 <td>Catalogue number</td>
 <td>Comments</td>
 </tr>
 <tr>
 <td>Bovine serum albumin</td>
 <td>Atlanta Biologicals</td>
 <td>S11750</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>PR8 virus</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 <td>From Dr Thomas M Moran</td>
 </tr>
 <tr>
 <td>Goat anti-mouse IRDye@800</td>
 <td>LI-COR biosciences</td>
 <td>926-32210</td>
 <td>1:200 dilution</td>
 </tr>
 <tr>
 <td>LI-COR Odyssey IR scanner</td>
 <td>LI-COR-biosciences</td>
 <td>9201-01</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>384-wells flat bottom plate</td>
 <td>Nalge Nunc international</td>
 <td>164730</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>96-wells flat bottom plate</td>
 <td>Nalge Nunc international</td>
 <td>165305</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>DMEM medium</td>
 <td>Invitrogen</td>
 <td>11965126</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>RPMI medium</td>
 <td>Invitrogen</td>
 <td>11875135</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Sodium bicarbonate</td>
 <td>Invitrogen</td>
 <td>25080</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>L-glutamine 100x</td>
 <td>Invitrogen</td>
 <td>25030</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Trypson-EDTA</td>
 <td>Invitrogen</td>
 <td>R001100</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Sodium Pyruvate</td>
 <td>Invitrogen</td>
 <td>11360070</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Anti-M-2 antibody</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 <td>From Dr Thomas M Moran</td>
 </tr>
 <tr>
 <td>Anti-NP mAb</td>
 <td>CDC</td>
 <td>V2S2208</td>
 <td>Obtained with an MTA</td>
 </tr>
 </tbody>
</table>

high-throughput detection method for influenza virus

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, precise diagnosis of the infecting strain and rapid high-throughput screening of vast numbers of clinical samples is paramount to control the spread of pandemic infections. Current clinical diagnoses of influenza infections are based on serologic testing, polymerase chain reaction, direct specimen immunofluorescence and cell culture 1,2.
Here, we report the development of a novel diagnostic technique used to detect live influenza viruses. We used the mouse-adapted human A/PR/8/34 (PR8, H1N1) virus 3 to test the efficacy of this technique using MDCK cells 4. MDCK cells (104 or 5 x 103 per well) were cultured in 96- or 384-well plates, infected with PR8 and viral proteins were detected using anti-M2 followed by an IR dye-conjugated secondary antibody. M2 5 and hemagglutinin 1 are two major marker proteins used in many different diagnostic assays. Employing IR-dye-conjugated secondary antibodies minimized the autofluorescence associated with other fluorescent dyes. The use of anti-M2 antibody allowed us to use the antigen-specific fluorescence intensity as a direct metric of viral quantity. To enumerate the fluorescence intensity, we used the LI-COR Odyssey-based IR scanner. This system uses two channel laser-based IR detections to identify fluorophores and differentiate them from background noise. The first channel excites at 680 nm and emits at 700 nm to help quantify the background. The second channel detects fluorophores that excite at 780 nm and emit at 800 nm. Scanning of PR8-infected MDCK cells in the IR scanner indicated a viral titer-dependent bright fluorescence. A positive correlation of fluorescence intensity to virus titer starting from 102-105 PFU could be consistently observed. Minimal but detectable positivity consistently seen with 102-103 PFU PR8 viral titers demonstrated the high sensitivity of the near-IR dyes. The signal-to-noise ratio was determined by comparing the mock-infected or isotype antibody-treated MDCK cells.
Using the fluorescence intensities from 96- or 384-well plate formats, we constructed standard titration curves. In these calculations, the first variable is the viral titer while the second variable is the fluorescence intensity. Therefore, we used the exponential distribution to generate a curve-fit to determine the polynomial relationship between the viral titers and fluorescence intensities. Collectively, we conclude that IR dye-based protein detection system can help diagnose infecting viral strains and precisely enumerate the titer of the infecting pathogens.

Watch this Scientific Journal Video about High-throughput Detection Method for Influenza Virus at JoVE.com

High-throughput Detection Method for Influenza Virus

This method describes the use of Infrared dye based imaging system for detection of H1N1 in bronchioalveolar lavage (BAL) fluid of infected mice at a high sensitivity. This methodology can be performed in a 96- or 384-well plate, requires &lt;10 &mu;l volume of test material and has the potential for concurrent screening of multiple pathogens.

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, ...

high-throughput-detection-method-for-influenza-virus

Research

JoVE Journal

Immunology and Infection

26.0K Views.  Blood Research Institute. This method describes the use of Infrared dye based imaging system for detection of H1N1 in bronchioalveolar lavage (BAL) fluid of infected mice at a high sensitivity. This methodology can be performed in a 96- or 384-well plate, requires 

Video: High-throughput Detection Method for Influenza Virus

Generation of Recombinant Influenza Virus from Plasmid DNA

Efforts by a number of influenza research groups have been pivotal in the development and improvement of influenza A virus reverse genetics. Originally established in 1999 1,2 plasmid-based reverse genetic techniques to generate recombinant viruses have revolutionized the influenza research field because specific questions have been answered by genetically engineered, infectious, recombinant influenza viruses. Such studies include virus replication, function of viral proteins, the contribution of specific mutations in viral proteins in viral replication and/or pathogenesis and, also, viral vectors using recombinant influenza viruses expressing foreign proteins 3.

Rescue of influenza A viruses from plasmid DNA is a basic and essential experimental technique that allows influenza researchers to generate recombinant viruses to study multiple aspects in the biology of influenza virus, and to be used as potential vectors or vaccines.

Efforts by a number of influenza research groups have been pivotal in the development and improvement of influenza A virus reverse genetics. Originally ...

Using Bioluminescent Imaging to Investigate Synergism Between Streptococcus pneumoniae and Influenza A Virus in Infant Mice

During the 1918 influenza virus pandemic, which killed approximately 50 million people worldwide, the majority of fatalities were not the result of infection with influenza virus alone. Instead, most individuals are thought to have succumbed to a secondary bacterial infection, predominately caused by the bacterium Streptococcus pneumoniae (the pneumococcus). The synergistic relationship between infections caused by influenza virus and the pneumococcus has subsequently been observed during the 1957 Asian influenza virus pandemic, as well as during seasonal outbreaks of the virus (reviewed in 1, 2). Here, we describe a protocol used to investigate the mechanism(s) that may be involved in increased morbidity as a result of concurrent influenza A virus and S. pneumoniae infection. We have developed an infant murine model to reliably and reproducibly demonstrate the effects of influenza virus infection of mice colonised with S. pneumoniae. Using this protocol, we have provided the first insight into the kinetics of pneumococcal transmission between co-housed, neonatal mice using in vivo imaging 3.

Using Bioluminescent Imaging to Investigate Synergism Between Streptococcus pneumoniae and Influenza A Virus in Infant Mice

A concurrent infection with influenza A virus is one of the factors implicated in the induction of invasive pneumococcal disease during asymptomatic Streptococcus pneumoniae carriage. Here we describe a mixed infection method using infant mice to investigate the synergism between these two respiratory pathogens.

During the 1918 influenza virus pandemic, which killed approximately 50 million people worldwide, the majority of fatalities were not the result of ...

ampliPHOX Colorimetric Detection on a DNA Microarray for Influenza

DNA microarrays have emerged as a powerful tool for pathogen detection.1-5 For instance, many examples of the ability to type and subtype influenza virus have been demonstrated.6-11 The identification and subtyping of influenza on DNA microarrays has applications in both public health and the clinic for early detection, rapid intervention, and minimizing the impact of an influenza pandemic. Traditional fluorescence is currently the most commonly used microarray detection method. However, as microarray technology progresses towards clinical use,1 replacing expensive instrumentation with low cost detection technology exhibiting similar performance characteristics to fluorescence will make microarray assays more attractive and cost-effective.
The ampliPHOX colorimetric detection technology is intended for research applications, and has a limit of detection within one order of magnitude of traditional fluorescence11, with a main advantage being an approximate ten-fold lower instrument cost compared to the confocal microarray scanners required for fluorescence microarray detection. Another advantage is the compact size of the instrument which allows for portability and flexibility, unlike traditional fluorescence instruments. Because the polymerization technology is not as inherently linear as fluorescence detection, however, it is best suited for lower density microarray applications in which a yes/no answer for the presence of a certain sequence is desired, such as for pathogen detection arrays. Currently the maximum spot density compatible with ampliPHOX detection is &tilde;1800 spots/array. Because of the spot density limitations, higher density microarrays are not suitable for ampliPHOX detection.
Here, we present ampliPHOX colorimetric detection technology as a method of signal amplification on a low density microarray developed for the detection and characterization of influenza viruses (FluChip). Although this protocol uses the FluChip (a DNA microarray) as one specific application of ampliPHOX detection, any microarray incorporating biotinylated target can be labeled and detected in a similar manner. The microarray design and biotinylation of the target to be captured are the responsibility of the user. Once the biotinylated target has been captured on the array, ampliPHOX detection can be performed by first tagging the array with a streptavidin-label conjugate (ampliTAG). Upon light exposure using the ampliPHOX Reader instrument, polymerization of a monomer solution (ampliPHY) occurs only in regions containing ampliTAG-labeled targets. The polymer formed can be subsequently stained with a non-toxic solution to improve visual contrast, followed by imaging and analysis using a simple software package (ampliVIEW). The entire FluChip assay from un-extracted sample to result can be performed in about 6 hours, and the ampliPHOX detection steps described above can be completed in about 30 min.

ampliPHOX colorimetric detection technology is presented as an inexpensive alternative to fluorescence detection for microarrays. Based on photopolymerization, ampliPHOX produces solid polymer spots visible to the naked eye in just a few minutes. Results are then imaged and automatically interpreted with a simple yet powerful software package.

DNA microarrays have emerged as a powerful tool for pathogen detection.1-5  For instance, many examples of the ability to type and subtype influenza virus ...

Influenza Virus Propagation in Embryonated Chicken Eggs

Influenza infection is associated with about 36,000 deaths and more than 200,000 hospitalizations every year in the United States. The continuous emergence of new influenza virus strains due to mutation and re-assortment complicates the control of the virus and necessitates the permanent development of novel drugs and vaccines. The laboratory-based study of influenza requires a reliable and cost-effective method for the propagation of the virus. Here, a comprehensive protocol is provided for influenza A virus propagation in fertile chicken eggs, which consistently yields high titer viral stocks. In brief, serum pathogen-free (SPF) fertilized chicken eggs are incubated at 37 &#176;C and 55-60% humidity for 10 &#8211; 11 days. Over this period, embryo development can be easily monitored using an egg candler. Virus inoculation is carried out by injection of virus stock into the allantoic cavity using a needle. After 2 days of incubation at 37 &#176;C, the eggs are chilled for at least 4 hr at 4 &#176;C. The eggshell above the air sac and the chorioallantoic membrane are then carefully opened, and the allantoic fluid containing the virus is harvested. The fluid is cleared from debris by centrifugation, aliquoted and transferred to -80 &#176;C for long-term storage. The large amount (5-10 ml of virus-containing fluid per egg) and high virus titer which is usually achieved with this protocol has made the usage of eggs for virus preparation our favorable method, in particular for in vitro studies which require large quantities of virus in which high dosages of the same virus stock are needed.

Fertile chicken eggs are widely used to produce large amounts of human influenza A virus as they provide a convenient and cost-effective system to prove high yields of virus.

Influenza infection is associated with about 36,000 deaths and more than 200,000 hospitalizations every year in the United States. The continuous ...

Nasal Wipes for Influenza A Virus Detection and Isolation from Swine

Surveillance for influenza A viruses in swine is critical to human and animal health because influenza A virus rapidly evolves in swine populations and new strains are continually emerging. Swine are able to be infected by diverse lineages of influenza A virus making them important hosts for the emergence and maintenance of novel influenza A virus strains. Sampling pigs in diverse settings such as commercial swine farms, agricultural fairs, and live animal markets is important to provide a comprehensive view of currently circulating IAV strains. The current gold-standard ante-mortem sampling technique (i.e. collection of nasal swabs) is labor intensive because it requires physical restraint of the pigs. Nasal wipes involve rubbing a piece of fabric across the snout of the pig with minimal to no restraint of the animal. The nasal wipe procedure is simple to perform and does not require personnel with professional veterinary or animal handling training. While slightly less sensitive than nasal swabs, virus detection and isolation rates are adequate to make nasal wipes a viable alternative for sampling individual pigs when low stress sampling methods are required. The proceeding protocol outlines the steps needed to collect a viable nasal wipe from an individual pig.

The authors present a protocol to collect swine nasal wipes to detect and isolate influenza A viruses.

Surveillance for influenza A viruses in swine is critical to human and animal health because influenza A virus rapidly evolves in swine populations and ...

In Vitro Disassembly of Influenza A Virus Capsids by Gradient Centrifugation

Acid-triggered molecular processes closely control cell entry of many viruses that enter through the endocytic system. In the case of influenza A virus (IAV), virus fusion with the endosomal membrane as well as the subsequent disassembly of the viral capsid, called uncoating, is governed by the ionic conditions inside endocytic vesicles. The early steps in the virus life cycle are hard to study because endosomes cannot be directly accessed experimentally, creating the need for an in vitro approach. Here, we describe a method based on velocity gradient centrifugation of purified virions through a two-layer glycerol gradient, which enables analysis of the IAV core and its stability. The gradient contains a non-ionic detergent (NP-40) in its lower layer to remove the viral membrane by solubilization as the virus sediments toward the bottom. At neutral pH, viral cores are pelleted as stable structures. The major core components, matrix protein (M1) and the viral ribonucleoproteins (vRNPs), can be clearly identified in the pellet fraction by SDS-PAGE. Decreasing the pH to 6.0 or lower in the bottom layer selectively removes M1 from the pellet followed by release of vRNPs at more acidic conditions. Viral protein bands on Coomassie-stained gels can be subjected to densitometric quantification to monitor intermediate states of IAV disassembly. Besides pH, other factors that influence viral core stability can be assessed, such as salt concentration and putative viral uncoating factors, simply by modifying the detergent-containing glycerol layer accordingly. Taken together, the presented technique allows highly reproducible and quantitative analysis of viral uncoating in vitro. It can be applied to other enveloped viruses that undergo complex uncoating processes.

In Vitro Disassembly of Influenza A Virus Capsids by Gradient Centrifugation

Disassembly of influenza A virus cores during virus entry into host cells is a multistep process. We describe an in vitro method to analyze the early stages of viral uncoating. In this approach, velocity gradient centrifugation is used to biochemically dissect the steps that initiate uncoating under defined conditions.

Acid-triggered molecular processes closely control cell entry of many viruses that enter through the endocytic system. In the case of influenza A virus ...

High-throughput Detection of Respiratory Pathogens in Animal Specimens by Nanoscale PCR

Nanoliter scale real-time PCR uses spatial multiplexing to allow multiple assays to be run in parallel on a single plate without the typical drawbacks of combining reactions together. We designed and evaluated a panel based on this principle to rapidly identify the presence of common disease agents in dogs and horses with acute respiratory illness. This manuscript describes a nanoscale diagnostic PCR workflow for sample preparation, amplification, and analysis of target pathogen sequences, focusing on procedures that are different from microliter scale reactions. In the respiratory panel presented, 18 assays were each set up in triplicate, accommodating up to 48 samples per plate. A universal extraction and pre-amplification workflow was optimized for high-throughput sample preparation to accommodate multiple matrices and DNA and RNA based pathogens. Representative data are presented for one RNA target (influenza A matrix) and one DNA target (equine herpesvirus 1). The ability to quickly and accurately test for a comprehensive, syndrome-based group of pathogens is a valuable tool for improving efficiency and ergonomics of diagnostic testing and for acute respiratory disease diagnosis and management.

High-throughput testing of DNA and RNA based pathogens by nanoscale PCR is described using a syndromic canine and equine respiratory PCR panel.

Nanoliter scale real-time PCR uses spatial multiplexing to allow multiple assays to be run in parallel on a single plate without the typical drawbacks of ...

Influenza A Virus Studies in a Mouse Model of Infection

Influenza viruses cause over 500,000 deaths worldwide1 and are associated with an annual cost of 12 - 14 billion USD in the United States alone considering direct medical and hospitalization expenses and work absenteeism2. Animal models are crucial in Influenza A virus (IAV) studies to evaluate viral pathogenesis, host-pathogen interactions, immune responses, and the efficacy of current and/or novel vaccine approaches as well as antivirals. Mice are an advantageous small animal model because their immune system is evolutionarily similar to that found in humans, they are available from commercial vendors as genetically identical subjects, there are multiple strains that can be exploited to evaluate the genetic basis of infections, and they are relatively inexpensive and easy to manipulate. To recapitulate IAV infection in humans via the airways, mice are first anesthetized prior to intranasal inoculation with infectious IAVs under proper biosafety containment. After infection, the pathogenesis of IAVs is determined by monitoring daily the morbidity (body weight loss) and mortality (survival) rate. In addition, viral pathogenesis can also be evaluated by assessing virus replication in the upper (nasal mucosa) or lower (lungs) respiratory tract of infected mice. Humoral responses upon IAV infection can be rapidly evaluated by non-invasive bleeding and secondary antibody detection assays aimed at detecting the presence of total or neutralizing antibodies. Here, we describe the common methods used to infect mice intranasally (i.n) with IAV and evaluate pathogenesis, humoral immune responses and protection efficacy.

Influenza A viruses (IAVs) are important human respiratory pathogens. To understand the pathogenicity of IAVs and to perform preclinical testing of novel vaccine approaches, animal models mimicking human physiology are required. Here, we describe techniques to evaluate IAV pathogenesis, humoral responses and vaccine efficacy using a mouse model of infection.

Influenza viruses cause over 500,000 deaths worldwide1 and are associated with an annual cost of 12 - 14 billion USD in the United States alone ...

Generation of Escape Variants of Neutralizing Influenza Virus Monoclonal Antibodies

Influenza viruses exhibit a remarkable ability to adapt and evade the host immune response. One way is through antigenic changes that occur on the surface glycoproteins of the virus. The generation of escape variants is a powerful method in elucidating how viruses escape immune detection and in identifying critical residues required for antibody binding. Here, we describe a protocol on how to generate influenza A virus escape variants by utilizing human or murine monoclonal antibodies (mAbs) directed against the viral hemagglutinin (HA). With the use of our technique, we previously characterized critical residues required for the binding of antibodies targeting either the head or stalk of the novel avian H7N9 HA. The protocol can be easily adapted for other virus systems. Analyses of escape variants are important for modeling antigenic drift, determining single nucleotide polymorphisms (SNPs) conferring resistance and virus fitness, and in the designing of vaccines and/or therapeutics.

We describe a method by which we identify critical residues required for the binding of human or murine monoclonal antibodies that target the viral hemagglutinin of influenza A viruses. The protocol can be adapted to other virus surface glycoproteins and their corresponding neutralizing antibodies.

Influenza viruses exhibit a remarkable ability to adapt and evade the host immune response. One way is through antigenic changes that occur on the surface ...

Rapid, Safe, and Simple Manual Bedside Nucleic Acid Extraction for the Detection of Virus in Whole Blood Samples

The rapid diagnosis of an infection is essential for the outbreak management, risk containment, and patient care. We have previously shown a method for the rapid bedside inactivation of the Ebola virus during blood sampling for safe nucleic acid (NA) tests by adding a commercial lysis/binding buffer directly into the vacuum blood collection tubes. Using this bedside inactivation approach, we have developed a safe, rapid, and simplified bedside NA extraction method for the subsequent detection of a virus in lysis/binding buffer-inactivated whole blood. The NA extraction is directly performed in the blood collection tubes and requires no equipment or electricity. 
After the blood is collected into the lysis/binding buffer, the contents are mixed by flipping the tube by hand, and the mixture is incubated for 20 min at room temperature. Magnetic glass particles (MGPs) are added to the tube, and the contents are mixed by flipping the collection tube by hand. The MGPs are then collected on the side of the blood collection tube using a magnetic holder or a magnet and a rubber band. The MGPs are washed three times, and after the addition of elution buffer directly into the collection tube, the NAs are ready for NA tests, such as qPCR or isothermal loop amplification (LAMP), without the removal of the MGPs from the reaction. The NA extraction method is not dependent on any laboratory facilities and can easily be used anywhere (e.g., in field hospitals and hospital isolation wards). When this NA extraction method is combined with LAMP and a portable instrument, a diagnosis can be obtained within 40 min of the blood collection.

Here, we present a protocol for the rapid virus nucleic acid extraction from the virus-inactivated whole blood. The extraction is performed directly in the blood collection tubes and requires no equipment or electricity. The method is not dependent on laboratory facilities and can be used anywhere (e.g., in field hospitals).

The rapid diagnosis of an infection is essential for the outbreak management, risk containment, and patient care. We have previously shown a method for ...