 Hello and welcome to Physiology Open. Aggressive testing for coronavirus is one important recommendation for identifying cases of coronavirus. But what are the fundamentals on which the diagnostic tests for coronavirus are created? Yes, that is the main subject of this video. So further we are going to discuss the fundamentals of pathogen diagnostics in general and of coronavirus in particular. For detecting the pathogens which have infected our body, we need to get an appropriate sample from the body and establish the presence of pathogen in the sample either directly or indirectly. Direct methods mean directly we see either the whole pathogen or recognize a part of it. And indirect means we assess the host's response to the pathogen. Choice of direct method depends on whether the pathogen can be cultured or not. That is whether the pathogen can be grown in a suitable environment or not. So for cultural pathogens, we can put the obtained sample in a suitable growth medium depending on the suspected pathogen and date for the pathogen to grow. Then we can stain it and observe the pathogen under the microscope. Culture and then staining is well established for bacterias where various culture media and stains like gram stain, gene lens and stain etc are available for different types of bacterias. So that is the reason why we should know the shape of the pathogens or shape of the colonies they form so that we can easily identify them under the microscope. Now all this cannot be done for non-culturable pathogen. For non-culturable pathogen we have to detect the presence of pathogen antigen which will directly establish the presence of the pathogen. These antigens are basically proteins present on the cell wall of the pathogen. See that's why we need to know about the structure of the pathogen. So these days we can directly detect the presence of pathogen nucleic acid. That is we can do the genetic test. For this first is detection of the genetic material of interest. So some complementary sequences of nucleic acids to the genetic material of interest known as primers are added which will attach to the nucleic acid of interest. It is possible because of the nucleic acid rule that is the adenine bonds with thymine and cytosine bonds with guanine. So if we know the genome of the pathogen we can easily know the complementary sequences of nucleic acid. Anyways the primers bind with the genetic material and once that happens it is amplified in quantity. This makes it possible to detect even small amounts of the nucleic acid present in the sample. So these tests are known as nucleic acid amplification test. For DNA viruses we may use polymerase chain reaction which amplifies the amount of DNA and for RNA viruses we use reverse transcriptase polymerase chain reaction which converts the RNA into its complementary DNA and then detects the presence of this complementary DNA. Now for indirect test we detect the host immune response to the pathogen. For host response we have to look for presence of IgM or IgG antibodies which develop against the host surface antigens or against the toxins produced by them. These are known as serological test but you can understand that it will take time for antibodies to develop right. Also the antibodies will be present even when the infection has resolved. So generally antibody detection is used for retrospective diagnosis that is to know whether the person was once infected with the pathogen or not because if the infection had resolved the pathogen would have disappeared right. So obviously direct test cannot be done. So how the presence of coronavirus is established? Well the sample for coronavirus is either nose or throat swab and since coronavirus is an RNA virus reverse transcriptase PCR is used to identify its genetic material. Now there is one problem. It can detect the virus only when it is present in a person. It gives no information if the person was infected earlier and now it got resolved. This is important because there may be some people who got infected but did not show any symptoms or very mild symptoms and were not tested for the presence of the pathogen. So for these people we need serological tests which will detect the presence of antibodies against the coronavirus implying that the person has already been infected with the virus. So these serological tests when done on a large scale will tell how many people had already been infected had produced antibodies and are possibly now immune to the infection right. But take note there may also be a possibility of reinfection which is not known till now. Now due to the lockdown in several countries across the world this knowledge will help us in returning life to normal. Obviously if there are minimal chances of reinfection because it will tell us which people are now immune to the pathogen and can move out. This is kind of a immunity ticket to move freely. Well the tests had already been developed but whether these will be useful for taking these kind of decisions it is still speculated ok. Thanks for watching the video. If you liked it do not forget to subscribe to the channel Physiology Open. Thank you.