[Various approaches to virologic diagnosis and the corresponding sampling]

Owing to the diversity of viral infections and to the high cost of laboratory techniques the diagnostic approach must be chosen according to clinical data. The two ways of approaching the viral diagnosis are of unequal value: detection of the virus or its constituents is preferable to detection of specific immune response. The virus or its constituents is either detected directly in the specimen collected (rapid diagnosis) or isolated after inoculation of a cellular system. Several methods can be used for rapid diagnosis: the virus may be visualized at electron microscopy; immunological techniques detect viral antigens bound to specific antibodies, the binding being revealed by immunofluorescence, enzyme-linked immunoassay or passive agglutination; detection of viral nucleic acids is particularly useful when the virus is difficult to isolate or the antigenic expression difficult to detect, or when immune response is deficient. Virus isolation from a cellular system is usually performed by cell cultivation. Typing of the isolated virus is effected by the same immunological methods os those used for rapid diagnosis, but also by seroneutralization of agglutination inhibition. Genic amplification, of CPR, is a special technique which detects the virus in the specimen studied after its genome has been amplified in an acellular system. Owing to technical problems and difficulties of interpretation, for the time being PCR is reserved to research. Success in diagnosis depends on the quality of the specimens and on their transfer to the laboratory under adequate conditions. Practitioners therefore play a major role in the diagnosis of viral diseases by prescribing the appropriate examinations, providing clinical information and making sure that the specimens are correctly collected.