A nylon membrane enzyme immunoassay for rapid diagnosis of influenza A infection

[Seasonal flu]

La grippe saisonnière est due aux virus influenza A et B. Il s’agit de virus enveloppés dont le génome est constitué de sept à huit fragments d’ARN. Les différents sous-types sont déterminés par la nature des deux glycoprotéines de surface HA et NA. La grippe saisonnière est une maladie épidémique et hivernale dans les zones à climat tempéré. Son épidémiologie est liée à la grande variabilité du virus au cours du temps, nécessitant la mise en place d’un système d’alerte détectant chaque année les variants circulants dominant et déterminant la composition vaccinale. Les symptômes cliniques de la grippe ne sont pas suffisamment spécifiques pour permettre le diagnostic sans examen virologique. Cela est particulièrement vrai en période non épidémique, chez les sujets de plus de 65 ans et chez les enfants de moins de cinq ans. L’enfant représente une cible privilégiée des infections à virus influenza. Le recours à l’hospitalisation est d’autant plus élevé que l’enfant est jeune. Chez le nourrisson, l’infection peut être paucisymptomatique et s’accompagner de manifestations non respiratoires (léthargie, convulsions, malaises). Le diagnostic virologique de la grippe est justifié chez tous les sujets hospitalisés pour un syndrome respiratoire compatible avec une infection à virus influenza. Il existe plusieurs outils permettant une recherche directe du virus dans les sécrétions respiratoires : isolement du virus en culture, détection d’antigènes, détection moléculaire de l’ARN. Le choix de la méthode se fait selon les caractéristiques du test : sensibilité, spécificité, rapidité et simplicité de réalisation, coût.

Viral diagnosis by antigen detection techniques

BACKGROUND

Diagnosis of viral infections can be obtained in the early stages of a disease by detection of viral antigens directly in the clinical specimen. This has become an important tool for rapid virus diagnosis.

METHODS

Antigens produced during virus infections can be detected either in cells collected from the site of infection by immunohistological investigation or in secretions and blood by solid phase immunoassays (IA). Viruses causing acute respiratory infections can be diagnosed in cells from the respiratory tract, viruses causing vesicular eruptions in epithelial cells from skin scrapings, rabies virus in nerve cells of the brain or epithelial cells from skin and cornea and cytomegalovirus (CMV) matrix antigen, pp65, can be detected in peripheral blood leukocytes (PBL) by immunofluorescence (IF) or immunoperoxidase techniques. The quality of specimens can be easily checked during the reading of results. Some IAs for antigen detection, such as detection of HBsAg and HIV p24 antigen in blood are standardized and sensitive. Others give less sensitive results because of the variation of quality of the clinical specimen. The latex agglutination tests are mainly used for rapid detection of virus or viral antigens in faeces: rota-and adenoviruses; the method may not be very sensitive but yields a result within a few minutes. Assays detecting viral nucleic acids are more sensitive than antigen detection tests because of a tremendous amplification of gene segments obtained by the polymerase chain reaction (PCR). So far such assays are time consuming and expensive and are mainly used in specific clinical situations.

RESULTS

After introduction of specific monoclonal antibodies (Mabs), the antigen detection techniques are increasingly used. the need for quality control, trained staff, and standardized reagents and methods for specimen collection and preparation is now being appreciated. IF for viral respiratory viruses is used for diagnosis and epidemiological studies all over the world. Likewise, IF is still the method most often used for rabies diagnosis. For CMV, the pp65 matrix antigen is shown to be a sensitive marker closely correlated with clinical symptoms. Its detection by the IF technique has proven to be superior to other techniques for prediction of CMV pneumonia in bone marrow transplant patients. IAs are currently used in fully automated systems for large scale diagnosis based on antigen detection in serum specimens. Increase of antibody specificity on the solid phase by use of Mabs directed against the most abundant viral antigen in the clinical specimen shortens the reaction time; this has been employed in most of the constantly appearing new rapid diagnosis kits based on the immunoassay principle.

CONCLUSION

Although, in virology, more sensitive results are obtained by the gene detection method, PCR, directly in clinical samples, viral antigen detection tests are, after the introduction of Mabs for diagnostic purposes, increasingly used because of their low demand on laboratory equipment, their rapid and early result and relatively low cost. Antigen detection is successfully used directly in clinical specimens for rapid diagnosis of many viral infections as well as for identification of tissue culture isolated viruses. With Mab-based IAs the reaction time is shortened and new rapid, almost 'instant test' kits are appearing on the market.

Influenza in the acute hospital setting

Influenza poses special hazards inside healthcare facilities and can cause explosive outbreaks of illness. Healthcare workers are at risk of acquiring influenza and thus serve as an important reservoir for patients under their care. Annual influenza immunisation of high-risk persons and their contacts, including healthcare workers, is the primary means of preventing nosocomial influenza. Despite influenza vaccine effectiveness, it is substantially underused by healthcare providers. Influenza can be diagnosed by culturing the virus from respiratory secretions and by rapid antigen detection kits; recognition of a nosocomial outbreak is important in order to employ infection-control efforts. Optimal control of influenza in the acute-care setting should focus upon reducing potential influenza reservoirs in the hospital, including: isolating patients with suspected or documented influenza, sending home healthcare providers or staff who exhibit typical symptoms of influenza, and discouraging persons with febrile respiratory illness from visiting the hospital during a known influenza outbreak in the community. (Note: influenza and other respiratory viruses can cause non-febrile illness but are still transmissible.) The antiviral M2 protein inhibitors (amantadine, rimantadine) and neuraminidase inhibitors (zanamivir, oseltamivir) have proven efficacy in treating and preventing influenza illness; however, their role in the prevention and control of influenza in the acute hospital setting remains to be more fully studied.

Rapid detection and identification of two lineages of influenza B strains with monoclonal antibodies

Monoclonal antibodies (Mabs) against influenza B virus were obtained by immunizing mice with B/Nagasaki/1/87, one of the strains of the B/Victoria group. Immunoprecipitation analysis revealed that individual Mabs precipitated the nucleoprotein (NP), the matrix protein (M) or the hemagglutinin protein (HA). By using these Mabs by the peroxidase-antiperoxidase (PAP) staining method, a rapid detection and identification method for influenza B virus was established. Monolayers of Madin-Darby canine kidney cells in microplates were infected with each-strain and incubated for about 24 h, and then were subjected to the PAP staining method using the Mabs as the first antibody. Influenza B virus strains are classified into two major phylogenetic trees, the B/Victoria group and the B/Yamagata group. When anti-NP and anti-M antibodies were used in the PAP staining method, all 13 influenza B virus strains isolated from clinical specimens between 1940 and 1994 were detected regardless of the antigenic drift of the influenza virus. On the other hand, several anti-HA Mabs which reacted specifically with the strains of the B/Victoria group, did not react with any strain of the B/Yamagata group. In the 1996/97 influenza season in Osaka Prefecture in Japan, two antigenically distinct groups of influenza B virus strains were isolated. They belonged to different phylogenetic trees and were clearly distinguishable by the PAP staining method with anti-HA Mabs.