Varizella-Zoster Virus IgA – ELISA

GWB-E7F6A9

Varicella-Zoster Virus (human herpes virus 3 HHV-3) belongs to the a-subfamily of herpesviridae. The virus particles measure about 145 nm in diameter. They consist of doublestranded DNA are surrounded by an icosahedral protein capsid and an envelope which contains both host cells and viral components. The virus is usually transmitted in respiratory secretions and a single serotype causes varicella (Chickenpox) a highly infectious childhood disease and zoster (shingles) a neurodermic disease; both diseases are found world-wide. Varicella is the acute disease which follows primary contact with the virus whereas zoster is the response of the partially immune host to a reactivation of the varicella virus present in the body in latent form. Varicella is endemic most commonly affected are children between 2 and 6 years of age. The course of disease is usually mild and complicated only in immunocompromised children. Rare fatal cases show multiple necrotic lesions in brain lung (varicella pneumonia) kidneys (hemorrhagic nephritis) spleen bone marrow and occasionally in the intestinal tract. The lethality of varicella is below 0. 1%. In the infrequent adult infections the disease is more severe and complications are to be expected in about 5% of all cases. Zoster is of low incidence and appears with increasing frequency and severity with advancing age. Usually the process remains localized generalization is frequently encountered in a state of immunosuppression. Fatal cases are very rare and nearly always caused by an underlying disease. The presence of virus resp. infection may be identified by:Microscopy: Giemsa stain; electron microscopy; IFSerology: Detection of antibody production by ELISAPrinciples of the assay: The qualitative immunoenzymatic determination of IgA-class antibodies against Varicella-Zoster Virus (VZV) is based on the ELISA (Enzyme-linked Immunosorbent Assay) technique. Microtiter strip wells are precoated with Varicella-Zoster Virus (VZV) antigens to bind corresponding antibodies of the specimen. After washing the wells to remove all unbound sample material horseradish peroxidase (HRP) labelled anti-human IgA conjugate is added. This conjugate binds to the captured Varicella-Zoster Virus (VZV)-specific antibodies. The immune complex formed by the bound conjugate is visualized by adding Tetramethylbenzidine (TMB) substrate which gives a blue reaction product. The intensity of this product is proportional to the amount of Varicella-Zoster Virus (VZV)-specific IgA antibodies in the specimen. Sulphuric acid is added to stop the reaction. This produces a yellow endpoint colour. Absorbance at 450 nm is read using an ELISA microwell plate reader. Storage and Stability: The reagents are stable up to the expiry date stated on the label when stored at 2. . . 8 & deg; C. Limitations of the Test: Bacterial contamination or repeated freeze-thaw cycles of the specimen may affect the absorbance values. Diagnosis of an infectious disease should not be established on the basis of a single test result. A precise diagnosis should take into consideration clinical history symptomatology as well as serological data. In immunocompromised patients and newborns serological data only have restricted value. References Croen K. D. S. E. Straus: VZV latency. Annu. Rev. Microbiol. 45 (1991) 265-285Dlugosch D. A. M. Eis-H& uuml; binger J-P. Klein et al. : Diagnosis of actute and latent VZVinfections using polymerase chain reaction. J. Med. Virol. 35 (1991) 136-141Enders G. VZV infections in pregnancy. Prog. med. Virol. 25 (1984) 166-196Harper D. R. H. O. Kangro R. B. Health: Serological responses in varizella and zoster assayed by immunoblotting. J. Med. Virol. 25 (1988) 387-398Health R. B. H. O. Kangro Varizella zoster. Inc: Zuckermann A. J. J. E. Banatvala J. R. Pattision (eds. ):Principles and Practice of Clinical Virology 2nd edition. John Wiley and Sons Chichester-New