[Kim Jaeho's Life Story]<178> The Vitality of Viruses

The novel coronavirus disease (COVID-19), so small that it cannot be seen with an optical microscope and can barely be observed through an electron microscope, is shaking the entire world. This virus, with a diameter of only 120 nanometers (1nm=10^-9m), is so tiny that it takes 80,000 of them lined up to make just 1 cm. What kind of abilities does this virus actually have?

Viruses are insignificant entities compared to any living organism in terms of structure and function. Unlike bacteria, which have cellular structures, viruses consist only of about ten genes made of DNA or RNA nucleic acids surrounded by a protein shell. They are not living organisms themselves but merely clumps of nucleic acids and proteins that cannot metabolize on their own, so they survive by parasitizing the cells of other living organisms called "hosts."

Since viruses cannot survive outside their hosts, the most important thing for a virus is its host. Only viruses that have the ability to find and move well to their hosts and proliferate effectively within them can survive.

The routes by which viruses move from one host to another vary depending on the type of virus. Plant viruses parasitizing plants move through vectors such as insects, while animal viruses parasitizing humans or animals move through various routes via infected bodily fluids. From the host's perspective, this movement results in viral infection.

Influenza viruses spread through the air when coughing or sneezing; noroviruses spread through contaminated hands, food, or water; rotaviruses spread through direct contact with infected individuals; human immunodeficiency virus (HIV) and hepatitis B and C viruses spread through bodily fluids during sexual activity or contaminated injections; and the novel coronavirus is currently believed to spread through respiratory secretions and direct contact.

Once a virus moves to a new host, it proliferates. Since viruses lack replication ability themselves, they make the host's cells replicate the virus's DNA or RNA and produce viral proteins. These combine to create numerous viruses. Compared to humans, who have about 20,000 to 25,000 genes, viruses have fewer genes (influenza virus has 8, rotavirus has 11), so their replication speed is very fast.

Diseases caused by viral infections, such as the common cold, influenza, chickenpox, measles, smallpox, poliomyelitis, acquired immunodeficiency syndrome (AIDS), hepatitis, severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and the currently prevalent COVID-19, show symptoms like high fever and coughing when the viral population exceeds a certain threshold (critical point). The period until symptoms appear is called the incubation period.

Viruses generally do not transmit to other hosts during the incubation period, but COVID-19 can be contagious even before the incubation period ends, making containment difficult. The medical community distinguishes the latent period, which is the time until contagiousness begins, from the incubation period. The latent period is shorter, so transmission during the symptomless incubation period can also be seen in HIV, which causes AIDS.

Cells infected by viruses die for various reasons. When many cells die?due to lysis or rupture of infected cells, deterioration of the cell membrane, self-destruction due to cell damage (apoptosis), or inability to function normally because of viral proteins?the function of organs like the respiratory system weakens, which can lead to death.

Humans and animals have multiple layers of defense to protect themselves from viral infections, which is the immune system that naturally cures diseases. The immune system exists in the body from birth and is divided into innate immunity, which defends against all types of bacteria and viruses indiscriminately, and adaptive immunity, which recognizes and eliminates specific bacteria or viruses by remembering them.

Innate immunity creates physical, chemical, and biological barriers such as skin that blocks viral invasion; mucus, coughing, and sneezing that expel viruses; mucus in the respiratory and gastrointestinal tracts; vomiting and diarrhea; and stomach acid that kills viruses. Viruses that penetrate these barriers are eliminated by white blood cells like T cells and natural killer (NK) cells that find and kill virus-infected cells.

Adaptive immunity involves B cells and T cells, types of white blood cells, that remember specific viruses and produce antibodies to prevent infection when the virus re-enters. Since one type of antibody attacks only one virus, adaptive immunity does not work against new viruses. Therefore, weakened or dead viruses are used as vaccines to produce antibodies against new viruses.

There is currently no medical method that can perfectly kill viruses without damaging normal cells and cure diseases by replacing the immune system when infected with a fatal viral disease. Because viruses only proliferate inside living cells, finding such a method will continue to be difficult.

Developing vaccines for prevention is effective but takes considerable time, and it is challenging to develop vaccines promptly for rapidly mutating viruses. There is also a limitation in that vaccines cannot be developed for all viruses. Antiviral drugs have been developed to suppress viral proliferation, but they cannot completely eliminate viruses, so their effectiveness is limited. Antibiotics are effective only against bacteria and are useless against viruses.

Many viral diseases frequently occur, and sometimes highly fatal influenza claims many lives, but most people either do not develop the disease or recover after infection. This is because our bodies have an excellent immune system prepared to overcome viral infections.

If you are worried about having contracted or contracting a viral disease due to weakened immunity, try to block viral infections and adopt a pro-life lifestyle that activates your life switch (see Life Story episode 68) to boost your immunity.

Kim Jae-ho, Independent Researcher