Question

Write any two biochemical/molecular diagonostic procedures for early detection of viral infection. Explain the principle of any one of them.

Answer 1

(i) Presence of a pathogen (bacteria, viruses, etc.) is normally suspected only when the pathogen has produced a disease symptom. By this time the concentration of pathogen is already very high in the body. However, very low concentration of a bacteria or virus (at a time when the symptoms of the disease are not yet visible) can be detected by amplification of their nucleic acid by PCR.
(ii) PCR is now routinely used to detect HIV in suspected AIDS patients. It is being used to detect
mutations in genes in suspected cancer patients too. It is a powerful techqnique to identify many other genetic disorders.
(iii) A single stranded DNA or RNA, tagged with a radioactive molecule (probe) is allowed to hybridise to its complementary DNA in a clone of cells followed by detection using autoradiography. The clone having the mutated gene will hence not appear on the photographic film, because the probe will not have complementarity with the mutated gene.
(iv) ELISA is based on the principle of antigen-antibody interaction. Infection by pathogen can be detected by the presence of antigens (proteins, glycoproteins, etc.) or by detecting the antibodies synthesised against the pathogen.