In 1983, Dr. Kary Mullis at Cetus Corporation conceived of polymerase chain reaction (Hersing, 1993). There is not any technique that has had a greater impact on the practice of molecular biology than PCR. With this technique, we can detect infectious disease agents at an extremely low level. It is based on the ability of sense and anti-sense DNA primers to hybridize to a DNA of interest. After extension from the primers on the DNA template by DNA polymerase, the reaction is heat-denatured and allowed to anneal with the primers once again. Another round of extension leads to a multiplicative increase in DNA products. Therefore, a minute amount of DNA can be efficiently amplified in an exponential fashion to result in easily manipulable amounts of DNA. By including critical controls, the technique can be made quantitative. The current level of the sensitivity and detection limit is as low as 10-50 copies per mL in HIV testing (Ginocchio et al., 2003). Important clinical examples of the use of PCR are detection of HIV and HCV (Abbott, 2003; Roche, 2003; Katsoulidou, 2004). PCR techniques have evolved into different branches. Some of them are now widely in use for virus detection in clinical diagnostics. These are real-time PCR by Taqman (Roche), Light Cycler (Roche), and Smart Cycler (Cepheid), and in situ PCR, nested-PCR, broad-range PCR, multiplex PCR, RT-PCR, arbitrarily primer PCR, long PCR, and quantitative PCR. Real-time sequence technology will be coming soon for more detailed detection. In the past, identification of viral serotypes was restricted to investigative methods using antibody detection and restriction fragment length polymorphism (RFLP). With real-time sequences technology, we will be able to detect a virus early as well as obtain the viral sequence.
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