Light Diagnostics™ Parainfluenza 1, 2, and 3 DFA is intended for the detection and identification of parainfluenza 1, parainfluenza 2, and parainfluenza 3 following amplification in cell culture.
For in vitro diagnostic use.
Test Principle:
Light Diagnostics Parainfluenza 1, 2, and 3 DFA Kit uses fluorescein- conjugated monolconal antibodies to identify virus in infected cells. The labeled antibodies will bind to antigen present in the cell. Unbound antigen is removed by washing. The antigen-antibody complex can be visualized by fluorescent microscopy. Positive specimens exhibit apple-green fluorescence while un-infected cells are stained a dull red.
Summary and Explanation:
Parainfluenza viruses belong to the genus Paramyxovirus of the family Paramyxoviridae. They are enveloped viruses with a single-strand RNA genome of negative polarity and range in diameter from 150 to 200 nm (20).
Along with RSV, parainfluenza viruses represent the most significant upper respiratory pathogens in infants and young chil-dren, but in older children and adults may be asymptomatic or mimic the common cold (1-3,5,16). Severe croup in early childhood or infancy may result in bronchial hyperactivity in older children or adolescents after exercise. However, it has yet to be determined whether bronchial hyperactivity is a pre-existing condition which plays a role in the pathogenesis of croup or whether it develops as a complication of severe croup (17,18).
Four types of parainfluenza viruses have been identified. Types 1 and 2 are major causes of laryngotracheo-bronchitis (croup), with greatest severity in children ages 2 to 4 years (6). Type 3 infection can also lead to croup but, most notably, is a major cause of infant bronchiolitis, pneumonia, and hospitalization, second only to RSV (8-11,15). Infection from type 3 virus is most severe in infants less than 1 year old (6). Parainfluenza type 4 has been associated only with mild upper respiratory illness in adults and children.
The advent of anti-viral therapy against some respiratory viruses makes rapid identification of these organisms imperative, allowing early and proper institution of therapy. The two most widely used anti-viral agents today are amantadine/rimantadine and ribavirin, both effecting early infection steps such as penetration or uncoating (12,19). Ribavirin has broad spectrum activity in vitro against a host of viruses such as RSV, measles, influenza A and B, as well as parainfluenza (7,13,14).
Three common mechanisms of identifying parainfluenza viruses are: culture isolation/confirmation, direct detection, and serology. Of these, culture isolation/confirmation is the gold standard and the most sensitive method available for detection. Culture is used to confirm negative direct detection findings and to identify co-infections.
Parainfluenza viruses grow well in primary simian kidney cell lines (RMK) and in LLC-MK2, a rhesus kidney heteroploid cell line (21). Parainfluenza infection of tissue culture can be recognized by hemadsorption of guinea pig erythrocytes. Types 2 and 3 can be recognized by syncytium formation, while type 4 is difficult to identify in cell cultures (6).