Enhancing effect of centrifugation on isolation of influenza virus from clinical specimens

Cultivation of PCV2 in swine testicle cells using the shell vial technique and monitoring of viral replication by qPCR and RT-qPCR

Porcine circovirus type 2 (PCV2) is difficult to isolate. Currently, no published articles have used the shell vial technique to isolate PCV2. In addition, the action of d-glucosamine on swine testicle cells (ST) has not been evaluated properly. Thus, the aim of this study was to determine an optimal concentration of d-glucosamine and to test the shell vial technique for PCV2 propagation in ST cells. The optimal concentration of d-glucosamine was determined to be 100mM. Because PCV2 is noncytopathic, the traditional adsorption was compared to the shell vial technique for 15 passages by qPCR, and RT-qPCR for passages 12 through 15. The quantities of viral DNA (P=0.013) and ORF1-mRNA detected with the shell vial technique were two-fold higher than the obtained with traditional adsorption. The levels of ORF2-mRNA were similar for both methods; however, by passage 15, a six-fold increase in levels was observed with the shell vial technique. Therefore, the shell vial technique was more efficient for the cultivation of PCV2, and qPCR/RT-qPCR can be used to monitor viral replication. In addition, a high viral load (>2.7×10(10) DNA copies/ml) and high levels of viral mRNA expression indicated that the ST cells were persistently infected.

Laboratory-based assessment of influenza in German ambulant patients from 1998 to 2008

BACKGROUND

In Germany, the cost for PCR diagnosis of influenza in ambulant patients was not covered by the national statutory health insurance system until 2008. Therefore, cell culture was the standard method applied for routine diagnosis. We have prospectively compared a 1-day rapid cell culture assay (RCA) with conventional cell culture (CCC) during the influenza seasons from 1997/1998 to 2007/2008 and with real-time PCR analysis during the influenza seasons 2003/2004 and 2006/2007.

PATIENTS AND METHODS

This study is based on 4,262 respiratory samples obtained from ambulant patients between January 1998 and May 2008. The RCA was performed in microtiter plates that were stained with monoclonal antibodies to influenza virus A and B 16 h after inoculation.

RESULTS

A total of 1,221 specimens were found to be positive by the cell culture methods - 1,143 (93.6%) by the RCA and 1,012 (82.9%) by the CCC. The sensitivity of the RCA and CCC versus PCR was 75.4% (221/293) and 58% (170/293), respectively. The specificity of both cell culture assays versus PCR was 100%. Influenza A represented 79.3% of the cases diagnosed. An increased activity of influenza was observed between January and March, with the rate of influenza-positive cases being highest for kindergarten and school-aged children.

CONCLUSION

While PCR is the most sensitive assay for the diagnosis of influenza, the RCA can still be used for diagnosis and surveillance of this disease. Based on our findings and given the known fact that influenza antibodies reach a plateau 2-4 weeks after immunization, the optimal time for vaccination in Germany is from October through November. Kindergarten and school-aged children represent an important reservoir of infection. Consequently, routine immunization should be considered for this age group to prevent the spread of influenza.

Comparison of the performance of the rapid antigen detection actim Influenza A&B test and RT-PCR in different respiratory specimens

Nowadays, influenza antigen detection test kits are used most frequently to detect influenza A or B virus to establish the diagnosis of influenza rapidly and initiate appropriate therapy. This study was conducted to evaluate the performance of the actim Influenza A&B test (Medix Biochemica). Overall, 473 respiratory specimens were analysed in the actim Influenza A&B test and the results were compared with those from an RT-PCR assay; 461 of these samples originated from paediatric patients aged 7 weeks to 6.5 years either with influenza-related symptoms or from the intensive care unit, and 12 samples originated from adults with underlying lung or haematological diseases. Diagnosis of influenza A or B virus could be established using the actim Influenza A&B test (9/473 samples for influenza A virus and 6/473 for influenza B virus). RT-PCR revealed 23 patients with influenza virus (13/473 for influenza A virus and 10/473 for influenza B virus). The sensitivity and specificity of the actim Influenza A&B test were 65 and 100 % compared with the RT-PCR assay. However, 32 external quality assessment samples containing seven different strains of influenza A subtypes H1N1 and H3N2 and the avian H5N1 were detected correctly by the actim Influenza A&B test. No cross-reactivity to a range of bacterial, fungal and other viral pathogens was observed. In conclusion, the actim Influenza A&B test is reliable for positive results due to its high specificity. Nevertheless, negative results from this test need to be confirmed by a more sensitive assay because of the low sensitivity observed with diagnostic samples.

Identification of influenza A virus by shell vial culture and two commercially available antigen detection methods

BACKGROUND

Effective use of amantidine and rimantidine for treating patients and for reducing transmission requires rapid diagnosis of influenza A. Rapid culture methods require 1-2 days to detect influenza A virus. Direct fluorescent antibody (DFA) staining and enzyme immunoassay (EIA) can detect influenza A antigen within 1-4 h.

OBJECTIVES

We compared DFA staining using the Bartels viral respiratory panel and the Directigen FLU-A EIA with shell vial centrifugation culture.

STUDY DESIGN

Ninety-seven fresh specimens from a variety of respiratory sources and transported from hospitals throughout the USA to our national referral laboratory were tested. A true positive was defined as culture positive or both antigen tests positive.

RESULTS

Fifteen specimens were true positive. Sensitivity with culture was 93%, EIA 67%, and DFA 47%. Specificity was excellent with all three methods: 100%, 98%, 99%. Culture detected additional viruses that can cause respiratory tract disease: herpes simplex, cytomegalovirus, respiratory syncytial, influenza B, and adenovirus. Fourteen (70%) of 20 frozen specimens previously positive for influenza A were positive on retest by EIA. Overall sensitivity of EIA compared with culture using 35 positive specimens was 69%.

CONCLUSIONS

These results suggest that the rapid EIA is useful to screen for influenza A, but that critical antigen-negative specimens should be submitted to a virology laboratory for culture for optimal sensitivity and for recovery of other viruses.

Identification of influenza A virus by shell vial culture and two commercially available antigen detection methods

BACKGROUND

Influenza continues to be a major cause of morbidity and mortality especially in the elderly and persons with underlying disease. Shell vial cell culture and antigen detection techniques may speed up diagnosis and enable better patient treatment and management.

OBJECTIVES

To compare shell vial centrifugation culture with commercially available direct fluorescence and enzyme immunoassay kits using a variety of respiratory specimens.

STUDY DESIGN

To detect influenza A virus, we compared direct fluorescent antibody (DFA) staining using the Bartels Viral Respiratory Panel and the Directigen FLU-A enzyme immunoassay (EIA) with shell vial centrifugation culture. Ninety-seven fresh specimens from a variety of respiratory sources, and transported from hospitals throughout the U.S. to our national referral laboratory, were tested.

RESULTS

Fifteen specimens were true positives: culture positive or both antigen tests positive. Sensitivity with culture was 93%, EIA 67%, and DFA 47%. Specificity was excellent with all three methods: 100%, 98%, 99%. Culture detected additional viruses that can cause respiratory tract disease: herpes simplex, cytomegalovirus, respiratory syncytial, influenza B, and adenovirus. Fourteen (70%) of 20 frozen specimens previously positive for influenza A were positive on retest by EIA. Overall sensitivity of EIA compared with culture using 35 positive specimens was 69%.

CONCLUSIONS

The rapid EIA is useful to screen for influenza A, but critical antigen-negative specimens should be submitted to a virology laboratory for culture. Shell vial cultures can provide a sensitive and universal diagnostic system for influenza A and a variety of other viruses.

Epidemiology of herpes simplex virus types 1 and 2 in Germany: what has changed?

Infections with herpes simplex virus (HSV) types 1 and 2 are widespread in all human populations and result in persistent and latent infections. HSV-1 is commonly responsible for orofacial, HSV-2 more likely causes genital lesions. Herpes genitalis is one of the most important sexually transmitted diseases; furthermore, there are severe diseases associated with HSV (e.g., encephalitis). Over the last years an increase in clinical manifestations of HSV has been reported, and HSV-1 has been increasingly discussed as causative agent of herpes genitalis. We retrospectively evaluated the laboratory results of our routine diagnostic service for HSV infections, looking for changes of HSV epidemiology in recent years. Specimens from 2,678 herpes patients were obtained between 1 January 1996 and 31 March 2002. Using cell culture, the presence of HSV was investigated in swabs taken from different body sites, and clinical data on HSV localization and type were evaluated. We found 345 patients positive for HSV-1 and 212 positive for HSV-2. Clinical data were available from 72.1% of the patients with HSV-1, and 61.3% of those with HSV-2 infection. In genital herpes HSV-1 was the causative agent in 20% of men and in 25% of women. In patients suffering from orofacial herpes HSV-2 was detected in 7% of men and in 4% of women. To evaluate the frequency of neurological HSV diseases, 2,406 cerebrospinal fluid samples (CSF) from 2,121 patients suspected of meningitis or encephalitis were tested for HSV DNA by the polymerase chain reaction. Among those patients, 120 showed CSF positive for HSV DNA. Serum surveys of HSV-1 and HSV-2 infection recently established in our region were compared to similar studies performed in Germany 25 years ago. We found that seroprevalences have not changed over the last 25 years and that neurological HSV diseases are rare. However, as in the USA, a significant percentage of herpes genitalis is caused by HSV-1 in Germany.

Evaluation of a rapid test (QuickVue) compared with the shell vial assay for detection of influenza virus clearance after antiviral treatment

QuickVue influenza rapid diagnostic test (Quidel Corp., San Diego, CA, USA) was compared with the classical shell vial assay for evaluation of influenza virus clearance in patients treated with antiviral drugs. The shell vial assay was carried out on nasopharyngeal samples obtained from volunteers for a neuraminidase-inhibitor clinical trial protocol with 24 h or less from the onset of symptoms of influenza before the use of antiviral (day 1). Follow-up included samples collected after 24 and 72 h of therapy (day 2 and 4). The rapid test was retrospectively carried out in frozen samples. Test results on 99 samples from 33 adults were compared and the shell vial assay was considered the gold standard. The overall rate of detection for the shell vial assay was 39.4% and for QuickVue was 35.5%, with a concordance of 79.8%. The sensitivity obtained for QuickVue was 74.4% and the specificity was 82.7%. Comparison of test results day by day in the follow-up resulted: day 1, higher sensitivity of QuickVue test (85.5%, 24/29); day 2, agreement on positive and negative results between QuickVue and shell vial was 60.6% (20/33); day 4, all test results in samples collected after 72 h of therapy were negative. The QuickVue test showed good sensitivity for the diagnosis of influenza-like illnesses. This rapid test kit can be an alternative tool for interventions in disease management.

Evaluation of a new dot blot enzyme immunoassay (directigen flu A+B) for simultaneous and differential detection of influenza a and B virus antigens from respiratory samples

We report a prospective evaluation of a new dot blot enzyme immunoassay (EIA) method for the direct, rapid, qualitative, simultaneous, and differential detection of the influenza A (IA) and B (IB) virus antigen in different respiratory samples. The EIA method was compared with the shell vial culture system (MDCK cell line) used with the same samples. We studied 160 samples from 93 (58.1%) pediatric patients (hospital emergency room) and from 67 (41.9%) adult patients (sentinel network). Seventy-four(46.2%) samples were considered positive; of them, 46 (62.2%) were from pediatric patients and 28 (37.8%) were from an adult group (P < 0.05), with overall positive values of 49.9% and 41.7%, respectively. All 74 (100%) of the positive samples were isolated in cell culture versus the 68.9% that were detected as positive by the new EIA method (P < 0.05). Of the 41 samples positive for the IA virus, the EIA detected 34 (82.9%) positive samples; of the 33 samples positive for the IB virus, the EIA detected 17 (51.5%) positive samples (P < 0.05). No false-positive reaction was detected with the EIA method (specificity and positive predictive value of 100%). The overall results obtained in the comparison between the new EIA and the shell vial culture had a sensibility of 82.9% and predictive negative values of 92.4% for the IA virus and 51.5% and 84.3%, respectively, for the IB virus. This evaluation shows sensitivity and specificity percentages for the new EIA method that is acceptable for routine use in IA virus detection. The results obtained were worse for IB virus detection, but this new EIA method is actually the only one with the capacity to differentiate between the two influenza viruses.

Comparison of Madin-Darby canine kidney cells (MDCK) with a green monkey continuous cell line (Vero) and human lung embryonated cells (MRC-5) in the isolation of influenza A virus from nasopharyngeal aspirates by shell vial culture

We report a comparative study of the MDCK, Vero, and MRC-5 cell lines in the isolation of the influenza A (IA) virus. We studied 746 samples in which 63 IA viruses were isolated. The MDCK line displayed 100% sensitivity, the Vero line displayed 71.4%, and the MRC-5 displayed 57.1%. The MDCK line showed a statistically significant difference with respect to the Vero line (P = 0.001) and the MRC-5 line (P = 0.001). The quantitative sensitivity analysis showed the MDCK line to be superior to the other lines. It seems that the MDCK line is still one of the most recommendable for the isolation of the IA virus from respiratory samples.

Evaluation of a direct immunofluorescence assay, dot-blot enzyme immunoassay, and shell vial culture in the diagnosis of lower respiratory tract infections caused by influenza A virus

We prospectively evaluated the efficacy of two commercial rapid methods for antigenic detection, a dot-blot enzyme immunoassay (EIA-DB) (Directigen FluA, Becton-Dickinson, USA) and a direct immunofluorescence assay (DIF) (Monofluokit Influenza A, Diagnostics Pasteur, France), compared with the shell-vial culture in the MDCK line, incubated 2 to 3 days and stained with the monoclonal antibody clone IA-52, the diagnosis of lower respiratory tract caused by Influenza A virus (IA). In the study period the presence of IA virus was detected in 59 of the 377 samples analyzed (15.7%). Only the SVC method detected all positive samples (100% sensitivity), being used as a reference method for comparison with the other techniques). The EIA-DB technique detected 50 cases (84.7%) and the DIF only 35 (59.3%). In nine (15.2%) cases the diagnosis was obtained only with the SVC method. The results of the comparison of the EIA-DB technique with SVC were: sensitivity 84.7%, specificity 100%, positive predictive value 100%, and negative predictive value 97.2%. The DIF technique gave values of 59.3%, 100%, 100%, and 92.9%, respectively. A statistically significant difference was observed between the sensitivity of the EIA-DB and the DIF method (p = 0.0001). In view of the results we recommended the use of the EIA-DB as a screening method when infection by the IA is suspected. But to obtain the maximum diagnostic yield all samples would be inoculated in a shell vial culture with the MDCK cell line.

Rapid culture for influenza virus, types A and B, in 96-well plates

BACKGROUND

Rapid diagnosis and typing of influenza virus are important for patient treatment and management during seasonal outbreaks. Centrifugation-enhanced rapid culture has been reported to be useful as an adjunct to traditional tube culture for rapid diagnosis of influenza virus.

OBJECTIVES

We compared rapid culture in 96-well plates against standard tube culture for recovery of influenza virus, types A and B. We also tested two different cell types, MDCK and RMK, to determine if the use of multiple cell lines increases the sensitivity of rapid culture.

STUDY DESIGN

The rapid method was initially evaluated by retrospective culture of previously positive frozen specimens. It was then compared to standard culture for recovery of influenza virus by parallel testing of fresh respiratory specimens.

RESULTS

Of 32 previously positive frozen specimens, 28 were positive upon repeat culture. Rapid culture recovered 25 (89.3%) and standard culture recovered 23 (82.1%). All positives were type A. Of 722 fresh specimens cultured in parallel, 76 (10.5%) were positive for influenza virus: 43 for type A and 33 for type B. For type A, rapid culture recovered 42 of 43 (97.7%) and tube culture recovered 39 (90.7%). For type B, rapid culture recovered 33 of 33 (100%) and tube culture recovered 24 (72.7%). In the rapid system, the MDCK cell line was positive for 40 of 42 type A positives (95.2%) and the RMK was positive for 41 (97.6%). The MDCK line was positive for 32 of the 33 type B isolates (97.0%) and the RMK cells were positive for all 33 (100%).

CONCLUSIONS

Rapid culture substantially reduced total test time and was more sensitive than tube culture. Duplicate cell lines did not significantly increase test sensitivity.

Enhancement of feline infectious peritonitis virus type I infection in cell cultures using low-speed centrifugation

The effects of centrifugation on the ability of feline infectious peritonitis virus (FIPV) to infect cells in culture was investigated. The infectivity titer was the highest when the plates were centrifuged at 400 x g (1500 rpm) for 2 h. All five strains classified as FIPV Type I showed infectivity titers enhanced 10-100-fold by centrifugation at 400 x g for 2 h. The centrifugal enhancement of infection was obtained only by centrifugation immediately after inoculation of the virus, suggesting that the enhancement occurs during attachment or adsorption of viruses to the cells. This method may be useful for the culture of FIPV Type I strains.

The use of MDCK, MEK and LLC-MK2 cell lines with enzyme immunoassay for the isolation of influenza and parainfluenza viruses from clinical specimens

Primary Monkey Kidney (PMK) epithelial cells or egg inoculation have been traditionally used for the culture of influenza and parainfluenza viruses. The high cost and variability of obtaining high quality PMK cells prompted us to investigate the use of other cell strains for the growth of these viruses. For this study we investigated three cell lines viz. MDCK, MEK and LLC-MK2 for the culture of influenza A and B and parainfluenza 1, 2 and 3 viruses. Clinical specimens were spun onto cell monolayers in microtitre wells. The growth of these viruses was then identified by specific antibodies in an enzyme immunoassay (EIA). The LLC-MK2 and MDCK cell lines were found to provide optimal growth of parainfluenza and influenza viruses respectively. During the period from November, 1990 to July, 1992, 6501 respiratory specimens were tested. There were 100 influenza A, 36 influenza B and 261 parainfluenza virus isolates. The influenza isolates were further subtyped by the WHO Influenza Reference Centre. The use of these cell lines and the EIA provided an effective method for the routine culture of these viruses.

Physical and chemical methods for enhancing rapid detection of viruses and other agents

Viral replication events can be enhanced by physical, chemical, or heat treatment of cells. The centrifugation of cells can stimulate them to proliferate, reduce their generation times, and activate gene expression. Human endothelial cells can be activated to release cyclo-oxygenase metabolites after rocking for 5 min, and mechanical stress can stimulate endothelial cells to proliferate. Centrifugation of virus-infected cultures can increase cytopathic effects (CPE), enhance the number of infected cells, increase viral yields, and reduce viral detection times and may increase viral isolation rates. The rolling of virus-infected cells also has an effect similar to that of centrifugation. The continuous rolling of virus-infected cultures at < or = 2.0 rpm can enhance enterovirus, rhinovirus, reovirus, rotavirus, paramyxovirus, herpesvirus, and vaccinia virus CPE or yields or both. For some viruses, the continuous rolling of infected cell cultures at 96 rpm (1.9 x g) is superior to rolling at 2.0 rpm for viral replication or CPE production. In addition to centrifugation and rolling, the treatment of cells with chemicals or heat can also enhance viral yields or CPE. For example, the treatment of virus-infected cells with dimethyl sulfoxide can enhance viral transformation, increase plaque numbers and plaque size, increase the number of cells producing antigens, and increase viral yields. The infectivity of fowl plague virus is increased by 80-fold when 4% dimethyl sulfoxide is added to culture medium immediately after infection. The heat shocking of virus-infected cells also has been shown to have a stimulatory effect on the replication events of cytomegalovirus, Epstein-Barr virus, and human immunodeficiency virus. The effects of motion, chemicals, or heat treatments on viral replication are not well understood. These treatments apparently activate cells to make them more permissive to viral infection and viral replication. Perhaps heat shock proteins or stress proteins are a common factor for this enhancement phenomenon. The utility of these treatments alone or in combination with other methods for enhancing viral isolation and replication in a diagnostic setting needs further investigation.

New aspects of influenza viruses

Influenza virus infections continue to cause substantial morbidity and mortality with a worldwide social and economic impact. The past five years have seen dramatic advances in our understanding of viral replication, evolution, and antigenic variation. Genetic analyses have clarified relationships between human and animal influenza virus strains, demonstrating the potential for the appearance of new pandemic reassortants as hemagglutinin and neuraminidase genes are exchanged in an intermediate host. Clinical trials of candidate live attenuated influenza virus vaccines have shown the cold-adapted reassortants to be a promising alternative to the currently available inactivated virus preparations. Modern molecular techniques have allowed serious consideration of new approaches to the development of antiviral agents and vaccines as the functions of the viral genes and proteins are further elucidated. The development of techniques whereby the genes of influenza viruses can be specifically altered to investigate those functions will undoubtedly accelerate the pace at which our knowledge expands.