[ELISA for diagnosis of infections by viruses]

The assay used most widely to detect or diagnose virus infection, especially infection of blood borne viruses e.g. HBV, HCV, HIV and HTLV, is the enzyme linked immunosorbent assay (ELISA), whose sensitivity and practicability have rendered it the most common primary screening assay. ELISA can be mass screening used automatic or semiautomatic machines. ELISAs can be indirect assay, competition assays or sandwich assays. In indirect and sandwich assays, the development of color indicates the presence of antigen or antibody, whereas in competition assays the absence of color development signifies a positive reaction. Alkaline phosphatase and horseradish peroxidase the most commonly used enzymes, are associated with their respective substrates, usually p-nitro-phenyl phosphate and hydrogen peroxide. The ELISA for antigen detection is used polyclonal antibody or monoclonal antibodies. The other hand, the ELISA for antibody screening is used whole virus, synthetic peptides or recombinant antigens.