Influenza viruses are categorized in type A, B, and C on the basis of the antigenic differences of their nucleoprotein (NP) and matrix (M1) proteins. Only type A and B are perceived to be clinically relevant in humans.
Influenza virus infections are the causal agents of recurrent epidemic of acute respiratory diseases in humans. In particular, influenza is highly contagious, can spread easily and is responsible for a considerable morbidity and mortality each year. Elderly and compromised individuals are especially at risk of developing severe illness and complications.
During epidemics influenza viruses can cause 10.000-20.000 deaths in the elderly and in patients with chronic cardiovascular and pulmonary diseases.
The clinical symptoms of influenza are very similar to those associated with other respiratory viruses, often circulating in the community at the same time. The immune response to influenza virus infection is influenced by the previous exposure history of the host to the influenza antigens. Serum antibodies appear in the 2nd week after the onset of the illness, reach peak titers by 4 weeks, and persist for months to years before gradually declining.
Serological diagnosis of acute influenza infection is completed by the detection of IgA-class, and in case of a second infection, by a fourfold or greater increase in the IgG titer between the acute-phase and the convalescent-phase sera.
Immunoenzymatic method for the qualitative determination of IgG and IgA-class antibodies to Influenza B in human serum. The test is based on the ELISA principle (Enzyme Linked ImmunoSorbent Assay) which uses the reaction between the antibodies present in the tested sample and the immobilized antigen bound to solid phases.The immunoglobulins bind to the antigen through incubation with diluted human serum. The result is expressed as an INDEX (ratio between the OD value of the sample and that of the Cut-off).