<Ul> <Li> The human immunodeficiency virus (or HIV), is a difficult target to find and eradicate . The earliest tests for infection relied on the presence of antibodies to the virus circulating in the bloodstream . However, antibodies don't appear until many weeks after infection, maternal antibodies mask the infection of a newborn, and therapeutic agents to fight the infection don't affect the antibodies . PCR tests have been developed that can detect as little as one viral genome among the DNA of over 50,000 host cells . Infections can be detected earlier, donated blood can be screened directly for the virus, newborns can be immediately tested for infection, and the effects of antiviral treatments can be quantified . </Li> <Li> Some disease organisms, such as that for tuberculosis, are difficult to sample from patients and slow to be grown in the laboratory . PCR - based tests have allowed detection of small numbers of disease organisms (both live or dead), in convenient samples . Detailed genetic analysis can also be used to detect antibiotic resistance, allowing immediate and effective therapy . The effects of therapy can also be immediately evaluated . </Li> <Li> The spread of a disease organism through populations of domestic or wild animals can be monitored by PCR testing . In many cases, the appearance of new virulent sub-types can be detected and monitored . The sub-types of an organism that were responsible for earlier epidemics can also be determined by PCR analysis . </Li> <Li> Viral DNA can be detected by PCR . The primers used must be specific to the targeted sequences in the DNA of a virus, and PCR can be used for diagnostic analyses or DNA sequencing of the viral genome . The high sensitivity of PCR permits virus detection soon after infection and even before the onset of disease . Such early detection may give physicians a significant lead time in treatment . The amount of virus ("viral load") in a patient can also be quantified by PCR - based DNA quantitation techniques (see below). </Li> <Li> Diseases such as pertussis (or whooping cough) are cause by the bacteria Bordetella pertussis . This bacteria is marked by a serious acute respiratory infection that affects various animals and humans and has led to the deaths of many young children . The pertussis toxin is a protein exotoxin that binds to cell receptors by two dimers and reacts with different cell types such as T lymphocytes which plays a role in cell immunity . PCR is an important testing tool that can detect the sequences that are within the pertussis toxin gene . This is because PCR has a high sensitivity for the toxin and has demonstrated a rapid turnaround time . PCR is very efficient for diagnosing pertussis when compared to culture . </Li> </Ul> <Li> The human immunodeficiency virus (or HIV), is a difficult target to find and eradicate . The earliest tests for infection relied on the presence of antibodies to the virus circulating in the bloodstream . However, antibodies don't appear until many weeks after infection, maternal antibodies mask the infection of a newborn, and therapeutic agents to fight the infection don't affect the antibodies . PCR tests have been developed that can detect as little as one viral genome among the DNA of over 50,000 host cells . Infections can be detected earlier, donated blood can be screened directly for the virus, newborns can be immediately tested for infection, and the effects of antiviral treatments can be quantified . </Li> <Li> Some disease organisms, such as that for tuberculosis, are difficult to sample from patients and slow to be grown in the laboratory . PCR - based tests have allowed detection of small numbers of disease organisms (both live or dead), in convenient samples . Detailed genetic analysis can also be used to detect antibiotic resistance, allowing immediate and effective therapy . The effects of therapy can also be immediately evaluated . </Li> <Li> The spread of a disease organism through populations of domestic or wild animals can be monitored by PCR testing . In many cases, the appearance of new virulent sub-types can be detected and monitored . The sub-types of an organism that were responsible for earlier epidemics can also be determined by PCR analysis . </Li>

The principle of polymerase chain reaction in identification of bacteria