Parainfluenza Virus IgA – ELISA

GWB-4A34B3

Parainfluenza viruses are important viral pathogens causing upper and lower respiratory infections in adults and children. The viruses belong to the family of Paramyxoviridae. They are enveloped single-stranded RNA viruses with spherical or pleomorphic shape. Parainfluenza viruses are relatively large viruses of about 150-300 nm in diameter. On the basis of antigenic differences they are divided into four subtypes of which type 4 is divided into two subtypes. Parainfluenza virus 1 and 3 belong to the paramyxovirus genus. Parainfluenza virus 2 4a and 4b belong to the rubella virus genus along with mumps. The virus is ubiquitous; infections occur as epidemics as well as sporadically. Parainfluenza viruses are sensitive to detergents and heat but can remain viable on surfaces for up to 10 hours. Transmission occurs via droplets aerosols and fomites (viruses survive on surfaces). Parainfluenza virus infections are primarily childhood diseases the highest age-specific attack rates for croup occur in children below the age of 3 years. Type 3 infections occur earliest and most frequently so that ~50% of children are infected during the first year of life and almost all by 6 years as determined by seroepidemiological studies. Antibodies against types 1 and 2 are acquired less rapidly but 80% of children have antibodies by 10 years of age. Type 4 viruses induce few clinical illnesses but infections are common 70 - 80% of children have antibodies by 10 years of age. In all age groups the incubation period appears to be five to six days. Croup or laryngotracheobronchitis is the commonest clinical manifestation of infection. Parainfluenza viruses are found uncommonly associated with other respiratory tract infections in children such as tracheobronchitis bronchiolitis and bronchopneumonia. Occasionally a mild non-specific illness is seen after parainfluenza virus infection. In adults the virus is usually limited to causing inflammation in the upper parts of the respiratory tract. Infections can be confirmed in two ways: by isolation and identification of the virus in cell culture or by direct detection of the virus in respiratory secretions (usually collected within one week of onset of symptoms) using immunofluorescence enzyme immunoassay or polymerase chain reaction assay andby demonstration of a significant rise in specific IgA antibodies between appropriately collected paired serum specimens or specific IgM antibodies in a single serum specimenPrinciples of the assay: The qualitative immunoenzymatic determination of IgA-class antibodies against Parainfluenza Viruses (Type 1 2 and 3) is based on the ELISA (Enzyme-linked Immunosorbent Assay) technique. Microwells are precoated with Parainfluenza Virus 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 Parainfluenza Virus-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 Parainfluenza Virus-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 readerStorage 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 American Academy of Pediatrics. Parainfluenza Viral Infections. In: Peter G ed. 1997 Red Book: Report of the Committee on Infectious Diseases. 24th ed. Elk Grove Village IL: American Academy of Pediatrics; 1997: 379. Collins PL Chanock RM McIntosh K. Parainfluenza viruses. In: Fields BN Knipe DM Howley PM eds. Fields Virology. 3rd ed. Philadelphia: Lippincott-Raven; 1995: 1205-41. Glezen WP Denny FW. Parainfluenza Viruses In: Evans A Kaslow R eds. Viral Infections in Humans: epidemiology and control. 4th ed. New York: Plenum; 1997:551-67.