Identification Of Influenza Viruses Research Articles

A second external quality assessment of isolation and identification of influenza viruses in cell culture in the Asia Pacific region highlights improved performance by participating laboratories.

Influenza viruses must be amplified in cell culture for detailed antigenic analysis and for phenotypic assays assessing susceptibility to antiviral drugs or for other assays. Following on from the first external quality assessment (EQA) for isolation and identification of influenza viruses using cell culture techniques in 2016, a follow up EQA was performed in 2019 for National Influenza Centres (NICs) in the World Health Organization (WHO) South East Asia and Western Pacific Regions. Nineteen WHO NICs performed influenza virus isolation and identification techniques on an EQA panel comprising 16 samples, containing influenza A or B viruses and negative control samples. One sample was used exclusively to assess capacity to measure a hemagglutination titer and the other 15 samples were used for virus isolation and subsequent identification. Virus isolation from EQA samples was generally detected by assessment of cytopathic effect and/or hemagglutination assay while virus identification was determined by real time RT-PCR, hemagglutination inhibition and/or immunofluorescence assays. For virus isolation from EQA samples, 6/19 participating laboratories obtained 15/15 correct results in the first EQA (2016) compared to 11/19 in the follow up (2019). For virus identification in isolates derived from EQA samples, 6/19 laboratories obtained 15/15 correct results in 2016 compared to 13/19 in 2019. Overall, NIC laboratories in the Asia Pacific Region showed a significant improvement between 2016 and 2019 in terms of the correct results reported for isolation from EQA samples and identification of virus in isolates derived from EQA samples (p=0.01 and p=0.02, respectively).

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

IntroductionHemagglutination (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 methodsA 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. ResultsThere 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. ConclusionsThis 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.

The first external quality assessment of isolation and identification of influenza viruses in cell culture in the Asia Pacific region, 2016

BackgroundThe isolation and propagation of influenza viruses from clinical specimens are essential tools for comprehensive virologic surveillance. Influenza viruses must be amplified in cell culture for detailed antigenic analysis and for phenotypic assays assessing susceptibility to antiviral drugs or for other assays. ObjectivesTo conduct an external quality assessment (EQA) of proficiency for isolation and identification of influenza viruses using cell culture techniques among National Influenza Centres (NICs) in the World Health Organisation (WHO) South East Asia and Western Pacific Regions. Study designTwenty-one NICs performed routine influenza virus isolation and identification techniques on a proficiency testing panel comprising 16 samples, containing influenza A or B viruses and negative control samples. One sample was used exclusively to determine their capacity to measure hemagglutination titer and the other 15 samples were used for virus isolation and identification. ResultsAll NICs performed influenza virus isolation using Madin Darby canine kidney (MDCK) or MDCK-SIAT-1 cells. If virus growth was detected, the type, subtype and/or lineage of virus present in isolates was determined using immunofluorescence, RT-PCR and/or hemagglutination inhibition (HI) assays. Most participating laboratories could detect influenza virus growth and could identify virus amplified from EQA samples. However, some laboratories failed to isolate and identify viruses from EQA samples that contained lower titres of virus, highlighting issues regarding the sensitivity of influenza virus isolation methods between laboratories. ConclusionThis first round of EQA was successfully conducted by NICs in the Asia Pacific Region, revealing good proficiency in influenza virus isolation and identification.

Seroconversion and immunogenicity evaluation of seasonal influenza vaccine in mice model.

Influenza virus is epidemiologically very important due to the antigenic variations occurring in it. In present study isolation and identification of influenza virus was attempted from Kasauli and adjoining areas. 71 clinical samples i.e. throat washings were processed and inoculated into the eggs for virus isolation. The isolated strains of H3N2, H1N1 and Influenza B were identified, purified and passaged in eggs. The harvested virus was inactivated by 0.03% formalin and three formulations of crude, inactivated, whole virus monovalent vaccine for H3N2, H1N1 and influenza B as well as a trivalent vaccine was prepared. The immunogenicity study of the vaccine was performed in the mouse model by using varying dilutions of four types of vaccines for a period of 40days. The impact of booster dose was also analyzed in the study. A significant seroconversion was observed in the mice sera verifying that the monovalent and trivalent lots of influenza vaccine were antigenically effective based on the serological tests.

Propagation and Characterization of Influenza Virus Stocks That Lack High Levels of Defective Viral Genomes and Hemagglutinin Mutations.

Influenza virus infections are responsible for more than 250,000 deaths annually. Influenza virus isolation, propagation, and characterization protocols are critical for completing reproducible basic research studies and for generating vaccine seed stocks. Detailed protocols for the isolation and identification of influenza virus have been recently reported (Eisfeld et al., 2014). However, there are few standardized protocols focused on the propagation and characterization of viral isolates, and as a result, viruses propagated in different conditions in different laboratories often have distinct in vitro and in vivo characteristics. Here, we focus on influenza A virus propagation and characterization in the laboratory taking into consideration the overall quality and composition of the virus stock to achieve consistency in virus yield, virulence, and immunostimulatory activity.

Native nucleic acid electrophoresis as an efficient alternative for genotyping method of influenza virus.

Influenza viruses are the worldwide major causative agents of human and animal acute respiratory infections. Some of the influenza subtypes have caused epidemics and pandemics among humans. The varieties of methods are available for the rapid isolation and identification of influenza viruses in clinical and environmental samples. Since nucleic acids amplification techniques such as RT-PCR have been adapted, fast and sensitive influenza type and subtype determination is possible. However, in some ambiguous cases other, more detailed assay might be desired. The genetic material of influenza virus is highly unstable and constantly mutates. It is known that single nucleotide polymorphisms (SNPs) results in resistance to commercially available anti-viral drugs. The genetic drift of the virus could also result in weakening of immune response to infection. Finally, in a substantial number of patients co-infection with various virus strains or types has been confirmed. Although the detection of co-infection or presence of minor genetic variants within flu-infected patients is not a routine procedure, a rapid and wide spectrum diagnostics of influenza virus infections could reveal an accurate picture of the disease and more importantly, is crucial for choosing the appropriate therapeutics and virus monitoring. Herein we present the evidences that native gel electrophoresis and MSSCP--a method based on multitemperature single strand conformation polymorphism could furnish a useful technique for minor variants, which escape discovery by conventional diagnostic assays.

IDENTIFICATION OF INFLUENZA VIRUSES IN HUMAN AND POULTRY IN THE AREA OF LARANGAN WET MARKET SIDOARJO-EAST JAVA, INDONESIA

Background: Influenza is a viral infection that attacks the respiratory system (nose, throat, and lungs) that commonly known as “flu”. There are 3 types of influenza viruses, such as type A, type B, and type C. Influenza virus type A is the type of virus that can infect both human and animals, virus type B are normally found only in human, and Influenza virus type C can cause mild illness in human and not causing any epidemics or pandemics. Among these 3 types of influenza viruses, only influenza A viruses infect birds, particularly wild bird that are the natural host for all subtypes of influenza A virus. Generally, those wild birds do not get sick when they are infected with influenza virus, unlike chickens or ducks which may die from avian influenza. Aim: In this study, we are identifying the influenza viruses among poultry in Larangan wet market. Method: Around 500 kinds of poultry were examined from cloacal swab. Result: Those samples were restrained with symptoms of suspected H5. The people who worked as the poultry-traders intact with the animal everyday were also examined, by taking nasopharyngeal swab and blood serum. Conclusion: Identification of influenza viruses was obtained to define the type and subtype of influenza virus by PCR.

The Evolving Threat of Influenza Viruses of Animal Origin and the Challenges in Developing Appropriate Diagnostics

An H1N1 subtype of swine origin caused the first influenza pandemic in this century. This pandemic strain was a reassortant of avian, swine, and human influenza viruses. Many diagnostic laboratories were overwhelmed by the testing demands related to this pandemic. Nevertheless, there remains the threat of other animal influenza viruses, such as highly pathogenic H5N1. As a part of pandemic preparedness, it is essential to identify the diagnostic challenges that will accompany the next pandemic. We discuss the natural reservoir of influenza viruses and the possible role of livestock in the emergence of pandemic strains. The current commonly used molecular tests for influenza diagnosis or surveillance are also briefly reviewed. Some of these approaches are also used to detect animal viruses. Unfortunately, owing to a lack of systematic surveillance of animal influenza viruses, established tests may not be able to detect pandemic strains that have yet to emerge from the animal reservoir. Thus, multiple strategies need to be developed for better identification of influenza viruses. In addition, molecular assays for detection of mutations associated with antiviral resistance and for viral segment reassortments should also be encouraged. Influenza viruses are highly dynamic viruses. Regular and systematic influenza surveillance in both humans and animals is essential to provide a more comprehensive picture of the prevalent influenza viruses. To better prepare for the next pandemic, we should develop some simple and easy-to-use tests for characterizing newly emerging influenza viruses.

Receptor specificity and erythrocyte binding preferences of avian influenza viruses isolated from India

IntroductionHemagglutination (HA) and hemagglutination inhibition (HI) assays are conventionally used for detection and identification of influenza viruses. HI assay is also used for detection of antibodies against influenza viruses. Primarily turkey or chicken erythrocytes [red blood cells (RBCs)] are used in these assays, as they are large, nucleated, and sediment fast, which makes it easy to determine the titer. Human influenza viruses agglutinate RBCs from chicken, human, and guinea pig, but not from horse. Human influenza viruses bind preferentially to sialic acid (SA) linked to galactose (Gal) by α 2, 6 linkage (SA α 2, 6-Gal), whereas avian influenza (AI) viruses bind preferentially to SA α 2, 3-Gal linkages. With this background, the present study was undertaken to study erythrocyte binding preferences and receptor specificities of AI viruses isolated from India.Materials and methodsA total of nine AI virus isolates (four subtypes) from India and three reference AI strains (three subtypes) were tested in HA and HI assays against mammalian and avian erythrocytes. The erythrocytes from turkey, chicken, goose, guinea pig and horse were used in the study. The receptor specificity determination assays were performed using goose and turkey RBCs. The amino acids present at 190 helix, 130 and 220 loops of the receptor-binding domain of the hemagglutinin protein were analyzed to correlate amino acid changes with the receptor specificity.ResultsAll tested highly pathogenic avian influenza (HPAI) H5N1 viruses reacted with all five types of RBCs in the HA assay; AI H9N2 and H5N2 viruses did not react with horse RBCs. For H5N1 viruses guinea pig and goose RBCs were best for both HA and HI assays. For H9N2 viruses, guinea pig, fowl and turkey RBCs were suitable. For other tested AI subtypes, avian and guinea pig RBCs were better. Eight isolates of H5N1, one H4N6 and one H7N1 virus showed preference to avian sialic acid receptors. Importantly, two isolates of HPAI H5N1, H9N2 and H11N1 viruses showed receptor specificity preference to both avian and mammalian sialic acid (α-2, 3 and α-2, 6) receptors.ConclusionsUse of different types of RBCs resulted in titer variations in HA and HI assays. This showed that RBCs giving optimum HA and HI titers would increase sensitivity of detection and would be more appropriate for identification and antigenic analysis of AI viruses. Analysis of 16 amino acids in the receptor-binding domain of the hemagglutinin of HPAI H5N1 viruses revealed that the only variation observed was in S221P amino acid position. Two H5N1 viruses showed S221P amino acid change, out of which only one H5N1 virus showed preference to α 2, 6 sialic acid receptor. One H5N1 virus isolate with amino acid S at 221 position, showed preference to α 2,3 as well as α 2,6 sialic acid receptors. This indicated that factor(s) other than S221P mutation in the hemagglutinin are probably involved in determining receptor specificity of H5N1 viruses. This is the first report of receptor specificity and erythrocyte binding preferences of AI viruses from India.

Clinical Accuracy of a PLEX-ID Flu Device for Simultaneous Detection and Identification of Influenza Viruses A and B

Respiratory tract infections caused by influenza A and B viruses often present nonspecifically, and a rapid, high-throughput laboratory technique that can identify influenza viruses is clinically and epidemiologically desirable. The PLEX-ID Flu assay (Abbott Molecular Inc., Des Plaines, IL) incorporates multilocus PCR and electrospray ionization-mass spectrometry to detect and differentiate influenza A 2009 H1N1 (H1N1-p), seasonal H1N1 (H1N1-s), influenza A H3N2, and influenza B viruses in nasopharyngeal swab (NPS) specimens. The clinical performance characteristics of the PLEX-ID Flu assay in symptomatic patients were determined in this multicenter trial. A total of 2,617 prospectively and retrospectively collected NPS specimens from patients with influenza-like illness between February 2008 and 28 May 2010 were eligible for inclusion in the study. Each specimen was tested in parallel by the PLEX-ID Flu assay and by the Prodesse ProFLU+ assay (Prodesse Inc., Madison, WI), to detect influenza A and B viruses. Specimens testing positive for influenza A virus by ProFLU+ were subtyped as H1N1-p, H1N1-s, or H3N2 by using the ProFAST+ assay (Gen-Probe Prodesse Inc.). The reproducibility of the PLEX-ID Flu assay ranged from 98.3 to 100.0%, as determined by testing a nine-specimen panel at three clinical sites on each of 5 days. Positive percent agreements (PPAs) and negative percent agreements (NPAs) of the PLEX-ID Flu assay were 94.5% and 99.0% for influenza A virus and 96.0% and 99.9% for influenza B virus, respectively. For the influenza A virus subtyping characterization, the PLEX-ID Flu assay had PPAs and NPAs of 98.3% and 97.5% for H1N1-p, 88.6% and 100.0% for H1N1-s, and 98.0% and 99.9% for H3N2, respectively. The overall agreements between the PLEX-ID and Prodesse ProFLU+/ProFAST+ assays were 97.1 to 100.0%. Bidirectional Sanger sequencing analysis revealed that 87.5% of 96 discrepant results between the PLEX-ID Flu and ProFLU+/ProFAST+ assays were found upon influenza A virus detection and H1N1-p subtyping. The PLEX-ID Flu assay demonstrated a high level of accuracy for the simultaneous detection and identification of influenza A and B viruses in patient specimens, providing a new laboratory tool for the rapid diagnosis and management of influenza A and B virus infections.

Burden and outcome of human influenza in a tertiary care hospital of Bangladesh

Objective To determine the magnitude and outcome of influenza in southern part of Bangladesh and also to identify intrusion of novel influenza virus. Methods This study was conducted for two years (2008–2009) in outpatient and inpatient department of both paediatrics and medicine discipline of Khulna Medical College Hospital. Nasal and throat swab specimens were collected from each influenza like illness (ILI) case and kept together in a virus transport media and transported to international centre for diarrhoeal disease and research, Bangladesh laboratory. Influenza virus was detected by rRT-PCR including types and subtypes. Results A total of 526 patients were enrolled during the study period with the mean (SD) age of 19 (17) years. Identification of influenza virus was 14% and positive cases were mostly found in under-five children (24%). The vast majority (88%) of influenza cases were found during April to September. Virus detection rate was higher in inpatient department (IPD) (21%) than in outpatient department (12%). The dominant virus type and subtype was influenza A (87%) and H3 (49%), respectively. Type A was significantly higher than type B in causing severe illness compared to ILI ( OR=7.04, 95% CI: 2.76–18.7, P<0.01). Headache and chest indrawing was found in significantly higher proportion ( P<0.05) in influenza positive IPD cases. Among 31 hospitalized cases majority (77%) recovered completely except two cases that needed referral for additional support. Conclusions Influenza mostly affected under-five children and young adult. The peak season here was late summer and rainy season.

Multifocal cerebral hemorrhages in H1N1 SOIV influenza patients: Report of 2 cases

Background: Neurological complications of influenza have been scarcely reported possible under-recognized. The full description of clinical forms of the current pandemic influenza is currently underway. Several different neurological syndromes have been associated with influenza but no cases of multi-focal cerebral hemorrhages have been reported so far. The aim of this report is to present 2 cases of multiple focal cerebral hemorrhages in patients with influenza H1N1 pandemic. Methods: Clinical, laboratorial and imaging data of 2 cases of influenza and serious neurological symptoms are presented. Cranial CT scan was performed in both cases. Influenza virus identification in upper respiratory secretion (UPS) was performed by real-timereversetranscriptase-polymerase-chain-reaction assay. Cerebrospinal fluid (CSF) was analized. No necropsy or brain biopsy were performed Results: Case n° 1: 32 years old pregnant woman with flu like symptoms, evolved to severe pneumonia and ARDS requiring mechanical ventilation. She developed comma and cranial CT scan has shown multiple hemorrhagic foci scattered throughout the brain and subaracnoid hemorrhage (SAH) (Figure 1). CSF was hemorrhagic. No hemorrhagic disorder was found and eclampsia was ruled-out. Despite oseltamivir therapy she eventually died. H1N1 SOIV was isolated from UPS. Case n° 2: 51 years old male with flu like symptoms evolved to ARDS and respiratory insufficiency demanding ICU and mechanical ventilation. He developed status epilepticus. Cranial CT scan showed multifocal hemorrhages. Lumbar CSF was hemorrhagic. H1N1 SOIV was isolated from UPS. Despite therapy with oseltamivir he eventually died. Figure 1: Cranial CT scan showing multifocal hemorrhage in frontal, parietal, temporal and occipital lobes, as well as SAH and intraventricular hemorrhage Conclusion: Influenza has imposed an under-recognized burden of central nervous system disease so far. Well known neurological syndromes associated with influenza virus in humans have been febrile convulsions, acute encephalitis, acute encephalopathy, Reye's syndrome, Guillain-Barré syndrome, Kleine-Levin syndrome and post encephalitic Parkinson's disease. Some encephalitis cases with petechial lesions in the brain have also been reported. The highly pathogenic H5N1 influenza virus has shown neurological damage in both birds and humans. Current medical literature, including some up-to-date publications of H1N1 pandemic haven’t shown the occurrence of multifocal hemorrhagic neurological syndromes. The cases here presented should aware practitioners for such possibility especially because many seriously ill influenza patients in ICU have been kept under sedation so hiding several neurological symptoms. Abstracts for SupplementInternational Journal of Infectious DiseasesVol. 14Preview Full-Text PDF Open Archive

Validation of A Fully Integrated Microfluidic Array Device for Influenza A Subtype Identification and Sequencing

Rapid detection and identification of influenza virus is becoming increasingly important in the face of concerns over an influenza pandemic. A fully integrated and self-contained microfluidic device has been developed to rapidly identify influenza A hemagglutinin and neuraminidase subtypes and sequence portions of both genes. The device consists of a DNA microarray with 12 000 features and a microfluidic cartridge that automates the fluidic handling steps required to carry out a genotyping assay for pathogen identification and sequencing. The fully integrated microfluidic device consists of microfluidic pumps, mixers, valves, fluid channels, reagent storage chambers, and DNA microarray silicon chip. Microarray hybridization and subsequent fluidic handling and reactions were performed in this fully automated and miniature device before fluorescent image scanning of the microarray chip. A micromixing technique based on gas bubbling generated by electrochemical micropumps was developed. Low-cost check valves were implemented in the cartridge to prevent cross talk of the stored reagents. The genotyping results showed that the device identified influenza A hemagglutinin and neuraminidase subtypes and sequenced portions of both genes, demonstrating the potential of integrated microfluidic and microarray technology for multiple virus detection. The device provides a cost-effective solution to eliminate labor-intensive and time-consuming fluidic handling steps and allows the detection and identification of influenza virus in a rapid and automated fashion.

Application of Molecular Biology Methods for Detection of Influenza Viruses in Bulgaria

ABSTRACTInfluenza viruses A and B are world-wide major causative agents of human acute respiratory infections. Three subtypes of HA (H1 to H3) and two subtypes of NA (N1 and N2) are found among influenza A viruses that have caused epidemics and pandemics among humans. For the rapid isolation and identification of influenza viruses in clinical samples variety of methods are available but the use of nucleic acid amplification techniques like RT-PCR has made sensitive diagnosis of influenza virus infection feasible, with the possibility of type and subtype determination. During the season 2002/2003 the laboratory of Influenza and ARD detected 7 type A and 4 type B influenza viruses by RT-PCR in 15 simulated samples from the respiratory panel from SEQC. In the season 2003/2004 - 42 positive results for influenza viruses subtype A/H3N2/were obtained by RT-PCR using specific HA and NA primer pairs from 50 nasal and throat swabs from patients with influenza-like diseases. The RT-PCR provides a sensitive and specific method for detecting, typing and subtyping influenza viruses A and B in clinical samples and can be used in the routine diagnosis of the disease in Bulgaria together with a large complex of classical methods.

Descriptive epidemiologic study of disease associated with influenza virus infections during three epidemics in horses.

To describe 3 epidemics of respiratory tract disease caused by influenza virus infections in a large population of horses. Cross-sectional and prospective longitudinal observational studies. All horses stabled at a Thoroughbred racetrack. During a 3-year period, descriptive information was collected as horses arrived at the racetrack and throughout race meetings. Routine observations and physical examinations were used to classify horses' disease status. Cause of epidemics was established by use of serologic testing and identification of influenza virus in nasal secretions. An epidemic of respiratory tract disease caused by influenza virus infections was identified during each year of the study. Attack rates of infectious upper respiratory tract disease (IURD) ranged from 16 to 28%. Incidence of disease caused by influenza virus infections during racing seasons in the second and third years was 27 and 37 cases/1,000 horses/mo, respectively. Physical distributions of stall locations revealed that affected horses were stabled throughout the population; horses affected later in epidemics were often clustered around horses affected earlier. Mucopurulent nasal discharge and coughing were observed in 83 and 62% of horses with IURD, respectively. Median duration of clinical disease was 11 days. Serologic testing was the most sensitive method used to detect influenza virus infections; 76% of affected horses seroconverted to influenza virus. Epidemics of IURD were observed annually in association with influenza virus infections. Few precautions were taken to limit spread of infection. Preventing or decreasing the likelihood of exposure and improving immunity in the population could substantially decrease risk of disease in similar populations.

Subtype-specific identification of influenza virus in cell cultures with FITC labelled egg yolk antibodies

We report on results obtained with a direct immunofluorescence test for subtype-specific identification of influenza virus in detached cells of MDCK cultures after inoculation of 281 clinical specimens from patients with influenza-like disease. Influenza virus antibodies were produced in eggs from immunized hens and labelled with FITC. In 157 cases CPE was found in MDCK cells. A total of 57 cases of influenza A (H3N2), 86 cases of influenza A (H1N1), and 14 cases of influenza B were identified. In 33 cases of influenza A (H1N1) infection with massive CPE guinea pig but not chicken erythrocytes were agglutinated by the cell culture supernatants. The single step immunofluorescence test described proved easy to perform and results were obtained within 1 h after CPE was observed in contrast to the conventional HIT which is very time-consuming.

DIRECT IDENTIFICATION OF INFLUENZA VIRUS IN THROAT WASHINGS BY MEANS OF CONCENTRATION AND MICRO-ASSAY.

SummaryA method of concentration and partial purification of influenza virus (A2) found in throat washings is described. A microtechnique is presented for identification of virus contained in the concentrates.The author wishes to thank Dr. Lajos Ccizmas, New York City Department of Health, for his generous gift of the Takatsy Plexiglas plates used in the micro-tests; Dr. Stephen Millian, Bureau of Laboratories, New York City Department of Health, for supplying the skim milk throat washings.The author is indebted to Dr. Benjamin Mandel, Public Health Research Institute of New York City, for valuable suggestions and encouragement.

Immunologic response of hamsters to influenza virus strains.

SummaryAntisera prepared in hamsters by the intranasal instillation of allantoic fluids containing influenza virus were type-specific when used in the complement-fixation test with the soluble antigens; group- or subtype-specific (e.g. A prime) when used in the complement fixation test with the allantoic fluid antigen, and strain-specific in hemagglutination-inhibition tests.It appears that the hamster is an animal best suited for quick identification of influenza viruses. It is suggested that their sera be used for systematic classification of strains.