PCR is a useful tool for early diagnosis of an Infectious disease. Elaborate.

Explanation

(i) The diagnosis and treatment of a particular disease often requires identifiying a particular pathogen.
(ii) Traditional methods of identification involve culturing these organisms from clinical specimens and performing metabolic and other tests to identify them.
(iii) PCR based diagonsis of infectious diseases is based on the fact that if the pathogen is present in a clinical specimen its DNA will be present. Its DNA has unique sequences that can be detected by PCR, often using the clinical specimen (for example, blood stool, spinal fluid, or sputum) in the PCR mixture.
(iv) PCR is also employed in the presental diagonsis of inherited diseases by using chorionic villi samples or cells from aminocentesis. Diseases like sickle cell anemia, `beta`- thalassemia and phenylketonuria can be detected by PCR in these samples.
(v) cDNA from PCR is a valuable tool for diagnosis and monitoring retroviral infections - Eg: Tuberculosis by Mycobacterium tuberculosis.
(vi) Several virally induced cancers, like cervical cancer caused by Papilloma virus can be detected by PCR.
(vii) Sex of human beings and live stocks, embryos fertilized invitro can be determined by PCR by using primers and DNA probes specific for sex chromosomes.
(viii) PCR technique is also used to detect sexlinked disorders in fertilized embryos.