Examples of traditional virological detection methods

Virus/virus antigen detection

Isolation of viruses in cell cultures A sample is inoculated onto cell cultures. Potential viruses use cells to reproduce, causing a cytopathogenic effect (CPE), i.e. they destroy the host cell. With the help of enzyme-marked antibodies, the viruses can be identified (red coloration).
Virus neutralisation test A sample is mixed with specific antibodies in a test tube. These antibodies neutralise the virus, which prevent it from infecting further cells.
Histological detection Tissues that could carry a virus are sliced very thinly and coated with specific enzyme-marked antibodies. The infected tissue will then change colour.
Detection of virus antigens with ELISA An inactivated virus is taken from a sample and mixed with specific enzyme-marked antibodies. The sample carrying the virus will then change colour.
Virus detection by electron microscope This method means that the virus can be viewed directly and identified.
Virus or antibody detection using special virus structures; haemagglutination The surface of some viruses (myxo- and paramyxoviruses) contains haemagglutinin, which causes red blood cells (erythrocytes) to clump (haemagglutinate).
Haemadsorption As the myxo- or paramyxoviruses reproduce, the presence of haemagglutinin is observed on the surface of infected cells. When these are mixed with erythrocytes, they adhere to the cell surface.

Antibody detection

Detection of viral antibodies with ELISA A patient blood sample is placed on a microtiter plate which is coated with an inactivated virus. Using another enzyme-marked antibody targeted at the patient’s antibodies, it is possible to identify whether virus specific antibodies are present in the blood sample.
Serum neutralisation test A blood sample containing antibodies is mixed with specific viruses in a test tube. These antibodies can neutralise the virus, which prevent it from infecting further cells.
Molecular biological detection Real-time (Reverse transcription-) PCR detection of a specific genome segment of a virus A soil sample is diluted in a test tube and viruses are eluted at high pH.. The viral RNA/DNA can then be extracted. In a real-time PCR cycler, the extracted nucleic acid can be identified using specific fluorescence-marked DNA probes.
Principle of real-time (RT-)PCR A specific segment of the extracted viral RNA / DNA is amplified and detected using specific DNA probes (primer & TaqMan probe) and an enzyme (polymerase). The double-stranded DNA is denatured into two individual strands. The primer and fluorescence-marked probe combine (anneal) with the single strand DNA. The sample is spiked with two fluorescent dyes: the quencher (Q) suppresses the fluorescence of the reporter (R). The polymerase recognises the double-stranded DNA primer and begins to synthesise the entire double strand (extension). In this way, the fluorescence-marked probe is split. The suppressed reporter dissolves in the solution and provides a measurable degree of fluorescence. This cycle, produced by denaturation at 95°C for 15 sec. and an annealing extension at 60°C for 60 sec, is repeated 40 times. After each cycle, the increase in DNA is measured quantitatively and presented in a fluorescence cycle diagram.