For a long time in the 20th century, techniques used to understand viruses involved; Isolation in cell lines and serology. In discovering the first existence of viruses, Dmitry Ivanovsky used experiments with filters. These filters had pores small enough to retain bacteria. The filtered solution had an infectious agent that was later named a Virus by Martinus Beijerinck. This filter was Known as a Chamberland filter and is what led to the discovery of the Tobacco Mosaic Virus. Over time Various virological techniques have been employed in diagnosing and characterizing viruses.
In his pursuit to develop a successful yellow fever vaccine, Max Theiler and his team managed to isolate the Yellow Fever virus. This was in 1927 which marks isolation of the first human virus. This success led to an increase in the number of serological studies considerably and also influenced the development of neutralizing antibody tests.
To simplify the detection of antibodies to yellow fever virus, Hemagglutination inhibition and complement fixation techniques became more advanced in the 1960s. First developed by American virologist George Hirst in 1941, Hemagglutination inhibition assay was used to quantify the relative concentration of viruses, bacteria, and antibodies. Complement fixation was used to detect the specific antigen in patient serum. It is based on the principle that when antigens and antibodies are mixed, complement gets fixed to the antigen-antibody complex. This activates the complement cascade and hemolysis occurs.
By the 1970s and 1980s viral detection had become more advanced with the development of insect cell cultures, Inoculation techniques for mosquitoes, electron microscopy, and immunofluorescence techniques. The discovery of HIV in the 1980s had a huge impact on the development of enzyme immunoassays (EIAs). This technique was used to visualize and quantify antigens.
In 1983, Karry Mullis conceived the Polymerase Chain Reaction (PCR) as a method for copying and synthesizing large amounts of target DNA. The isolation of Taq polymerase in 1986 streamlined and shortened this process due to the thermostability of the enzyme. PCR is currently the method of choice for detecting viral nucleic acids as it allows for the studies of most acute and chronic viral infections. In the last few years, several technologies and methodological PCR approaches have been adopted for semiquantitative and qualitative analysis of Viral Nucleic acids. This has benefited the monitoring of viral load as a useful indicator of disease progression.
We currently have a wide range of automated techniques giving virologists various options to characterize and understand viruses. Capillary electrophoresis-based Sanger sequencing has enabled scientists to generate genetic information on any given biological system. It has routinely been used for HIV and HEP B sequencing. Due to its low throughput, scalability, and speed, Sanger sequencing limitations led to the development of the Next Generation Sequencing (NGS) technologies. NGS has been used to detect and characterize viruses from their full-length genome. It has also enabled the monitoring of antiviral drug resistance.
In these exciting times, newer techniques and other molecular detection methods will continue shaping discoveries and expansion of our knowledge on Viruses. Challenges faced in the earlier days will still be felt in this new era. However, with the improvements witnessed over time, a lot is expected and modern techniques are likely to become more sensitive with high throughput and high efficiency.