Viruses are the most abundant biological form of life on the planet. Diseases caused by them have claimed a lot of lives over the centuries. Viruses are so common today. Some of them cause viral infections which can cause minor diseases, such as a cold or the stomach flu. But some viruses can cause severe diseases, which can be fatal for humans. If they spread really fast and easily, it is possible they can take epidemic and pandemic scales, and cause a huge negative impact on the whole world and the society.
But what really viruses are? How bad can they be? Or can we protect ourselves from them? Let's find out.
In this lesson, we are going to learn about VIRUSES, and we will discuss:
Viruses are infectious agents of small size and simple composition that can multiply only in living cells of animals, plants, or bacteria. The name comes from a Latin word meaning “slimy liquid” or “poison.” Viruses have both living and nonliving characteristics, so they can not be classified in any of the five kingdoms of living things, meaning they are not bacteria, fungi, protists, plants, or animals.
Viruses are microscopic particles that exist almost everywhere on Earth. They cannot be seen with an optical microscope, because most of them are so small.
Viruses are present in animals, plants, and other living organisms.
Specific for viruses is that they can only thrive and multiply in a host. A host can be any living thing, such as a human, an animal, or a plant. The same virus may also affect one organism in one way but a different organism in another way. This explains why a virus that causes illness in a dog or a cat may not affect a human, and opposite.
Viruses that infect only bacteria are called bacteriophages and those that infect only fungi are called mycophages. There are even viruses that can infect other viruses, they are called virophages.
The study of viruses and virus-like agents is called virology.
The first human virus discovered was the yellow fever virus in 1901 by Walter Reed, who was U.S. Army pathologist and bacteriologist.
Viruses are bad because sometimes they cause diseases. Those diseases are called viral diseases. Viral diseases in some cases are contagious, meaning they can be transmitted from person to person in many ways; through touch, saliva, or even the air. Some viruses can be transmitted through sexual contact or by sharing contaminated needles. Insects including ticks and mosquitoes can act as "vectors," transmitting a virus from one host to another. Contagious viral diseases include the flu, the common cold, HIV, COVID-19, etc. But, not always viral diseases are contagious.
Viruses consist of genetic material, DNA or RNA, with a coat of protein around them. Some have an additional coat called the envelope. This may be spiky and helps them latch onto and enter host cells. The only way viruses replicate is in a host, such as a human, an animal, or a plant.
Most viruses are made up of the same basic parts which include:
The genetic material carried by the virus can cause a wide variety of diseases, ranging from the common cold to more serious longer-lasting diseases such as HIV.
When a virus gets inside of an organism, like a human, or another animal, its genetic material allows it to damage or change cells in order to multiply rapidly. And if the immune system can't fight it off, the viral illness can cause damage. Sometimes, damage can be fatal.
Viruses vary in size. Most viruses vary in diameter from 20 nanometres (nm; 0.0000008 inches) to 250–400 nm. The largest viruses measure about 500 nm in diameter and are about 700–1,000 nm in length.
Viruses vary in shape. Shapes of viruses are predominantly of two kinds:
The following viruses are among many viruses that exist:
Dengue virus, Hepatitis (A, B, C, E), Human adenovirus, Human enterovirus, Human herpesvirus, Human papillomavirus, Human SARS coronavirus, Influenza viruses, Measles virus, Poliovirus, Rotaviruses, Yellow fever virus, Zika virus, Varicella-zoster virus, Variola virus, SARS coronavirus 2.
Each of these viruses can cause infectious diseases among humans.
When it comes into contact with a host cell, a virus can insert its genetic material into its host, taking over the host's functions. An infected cell produces more viral protein and genetic material instead of its usual products. Some viruses may remain dormant inside host cells for long periods, causing no obvious change in their host cells. But when a dormant virus is stimulated new viruses are formed, self-assemble, and burst out of the host cell, killing the cell and going on to infect other cells.
The immune system is designed to monitor, recognize, and even remember the virus and take action to eliminate it, when a virus invades healthy cells.
T cells are a part of the immune system that focuses on specific foreign particles. They are important white blood cells of the immune system, that play a critical part in immunity to foreign substances. The immune system produces a battalion of T cells that can target viruses. If the T cell receptor detects a peptide from a virus, it warns its T cell of an infection, so the T cell releases cytotoxic factors to kill the infected cell and, therefore, prevent the survival of the invading virus.
Antibodies are one of the key weapons against viruses in our immune system. Antibodies are large, Y-shaped proteins used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the pathogen, called an antigen. They help the body fight against viruses.
Once a person is infected with a virus, their body becomes a reservoir of virus particles that can be released in bodily fluids. Common ways of spreading are through:
Some viruses spread more easily than others.
Vaccines are used to successfully prevent some viruses. A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease. Mass vaccination has helped to stop the spread of many viral infections.
Antibiotics do not work against viruses, they can only cure bacterial diseases and infections.
For treating viral infections there is a class of medications, called Antiviral drugs. They help the body fight off certain viruses that can cause diseases. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses.
The following are measures that we can take to protect ourselves from viruses:
