What is a Virus

Viruses are microscopic organisms that exist almost everywhere on earth. They can infect animals, plants, fungi, and even bacteria.

Sometimes a virus can cause a disease so deadly that it is fatal. Other viral infections trigger no noticeable reaction. A virus may also have one effect on one type of organism, but a different effect on another. This explains how a virus that affects a cat may not affect a dog. Viruses vary in complexity. They consist of genetic material, RNA or DNA, surrounded by a coat of protein, lipid (fat), or glycoprotein. Viruses cannot replicate without a host, so they are classified as parasitic. They are considered the most abundant biological entity on the planet.

Viral disease definition: Viruses are very small infectious agents. They’re made up of a piece of genetic material, such as DNA or RNA, that’s enclosed in a coat of protein. Viruses invade cells in your body and use components of those cells to help them multiply. This process often damages or destroys infected cells. A viral disease is any illness or health condition caused by a virus.

Key points about Viruses:

*Viruses are living organisms that cannot replicate without a host cell.

*They are considered the most abundant biological entity on the planet.

*Diseases caused by viruses include rabies, herpes, and Ebola.

*There is no cure for a virus, but vaccination can prevent them from spreading

Almost every ecosystem on Earth contains viruses. Before entering a cell, viruses exist in a form known as virions. During this phase, they are roughly one-hundredth the size of a bacterium and consist of two or three distinct parts:

*genetic material, either DNA or RNA

*a protein coat, or capsid, which protects the genetic information

*a lipid envelope is sometimes present around the protein coat when the virus is outside of the cell

Viruses do not contain a ribosome & they cannot make proteins. This makes them totally dependent on their host. They are the only type of microorganism that cannot reproduce without a host cell. After contacting a host cell, a virus will insert genetic material into the host and take over that host's functions. After infecting the cell, the virus continues to reproduce, but it produces more viral protein and genetic material instead of the usual cellular products. It is this process that earns viruses the classification of parasite. Viruses have different shapes and sizes, and they can be categorized by their shapes.

These may be:

*Helical: The tobacco mosaic virus has a helix shape.

*Icosahedral, near-spherical viruses: Most animal viruses are like this.

*Envelope: Some viruses cover themselves with a modified section of cell membrane, creating a protective lipid envelope. These include the influenza virus and HIV.

Other shapes are possible, including nonstandard shapes that combine both helical and icosahedral forms. Viruses do not leave fossil remains, so they are difficult to trace through time. Molecular techniques are used to compare the DNA and RNA of viruses and find out more about where they come from. Three competing theories try to explain the origin of viruses:

  • Regressive, or reduction hypothesis: Viruses started as independent organisms that became parasites. Over time, they shed genes that did not help them parasitize, and they became entirely dependent on the cells they inhabit.

  • Progressive, or escape hypothesis: Viruses evolved from sections of DNA or RNA that "escaped" from the genes of larger organisms. In this way, they gained the ability to become independent and move between cells.

  • Virus-first hypothesis: Viruses evolved from complex molecules of nucleic acid and proteins either before or at the same time as the first cells appeared on Earth, billions of years ago

Transmission: A virus exists only to reproduce. When it reproduces, its offspring spread to new cells and new hosts. The makeup of a virus affects its ability to spread. Viruses may transmit from person to person, and from mother to child during pregnancy or delivery. They can spread through:

  • touch

  • exchanges of saliva, coughing, or sneezing

  • sexual contact

  • contaminated food or water

  • insects that carry them from one person to another

Some viruses can live on an object for some time, so if a person touches an item with the virus on their hands, the next person can pick up that virus by touching the same object. The object is known as a fomite. As the virus replicates in the body, it starts to affect the host. After a period known as the incubation period, symptoms may start to show.

Many Neurologic Viruses are spread through the bite of an infected animal or bug, such as a mosquito or tick. Other viruses, such Poliovirus and other Enteroviruses, are quite contagious and spread through close contact with someone with the virus. Contaminated objects can also contribute to the spread of these viruses.

Some Hemorrhagic Viral Diseases, such as Dengue Fever and Yellow Fever, are spread through the bite of an infected insect. Others, such as Ebola, are spread to other people through contact with the blood or other bodily fluid of someone with the virus. Lassa fever is spread through inhaling or consuming the dried feces or urine of a rodent with the virus.

What happens if viruses change? When a virus spreads, it can pick up some of its host's DNA and take it to another cell or organism. If the virus enters the host's DNA, it can affect the wider genome by moving around a chromosome or to a new chromosome. This can have long-term effects on a person. In humans, it may explain the development of Hemophilia and Muscular Dystrophy.

This interaction with host DNA can also cause viruses to change. Some viruses only affect one type of being, say, birds. If a virus that normally affects birds does by chance enter a human, and if it picks up some human DNA, this can produce a new type of virus that may be more likely to affect humans in future. This is why scientists are concerned about rare viruses that spread from animals to people.

Viral diseases: Viruses cause many human diseases. These include:

  • Smallpox

  • Common Cold and different types of Flu

  • Measles, Mumps, Rubella, Chicken Pox and Shingles

  • Hepatitis

  • Herpes and Cold Sores

  • Polio

  • Rabies

  • Ebola and Hanta fever

  • HIV, the virus that causes AIDS

  • Severe Acute Respiratory Syndrome (SARS)

  • Dengue fever, Zika, and Epstein-Barr

Some viruses, such as the human papilloma virus (HPV), can lead to cancer.

Hepatic viral diseases: The hepatic viral diseases cause inflammation of the liver, known as viral hepatitis. The most common types of viral hepatitis are hepatitis A, B, and C. It is worth noting that diseases caused by other viruses, such as Cytomegalovirus, the Yellow Fever Virus and Dengue Fever, can also affect the liver. Examples of Hepatic Viral Diseases include: Hepatitis A, B, C, D, E.

When the body's immune system detects a virus, it starts to respond, to enable cells to survive the attack. A process called RNA interference breaks down the viral genetic material. The immune system produces special antibodies that can bind to viruses, making them non-infectious. The body sends T cells to destroy the virus. Most viral infections trigger a protective response from the immune system, but viruses such as HIV and Neurotropic viruses have ways of evading the immune system's defenses. Neurotropic viruses infect nerve cells. They are responsible for diseases such as polio, rabies, mumps, and measles. They can affect the structure of the Central Nervous System (CNS) with delayed and progressive effects that can be severe.

Cutaneous Viral Diseases: Cutaneous viral diseases cause lesions or papules to form on the skin. In many cases, these lesions can stick around for a long time or come back after disappearing for a while. Examples of cutaneous viral diseases include:

  • warts, including genital warts

  • oral herpes

  • genital herpes

  • molluscum contagiosum

Hemorrhagic Viral Diseases: are severe conditions that involve damage to your circulatory system. Symptoms of a hemorrhagic viral disease include:

  • high fever

  • body aches

  • weakness

  • bleeding under the skin

  • bleeding from the mouth or ears

  • bleeding in internal organs

Examples of viral hemorrhagic diseases include:

  • Ebola

  • Lassa fever

  • Dengue fever

  • Yellow fever

  • Marburg hemorrhagic fever

  • Crimean-Congo hemorrhagic fever

Treatment: There’s no specific treatment for hemorrhagic viral diseases. It’s important to stay hydrated if you have a viral hemorrhagic disease. Some people may need intravenous (IV) fluids to maintain electrolyte balance. Supportive care to maintain hydration and electrolyte balance is essential. In some cases, the antiviral drug ribavirin may be given. Hemorrhagic viral diseases can be fatal.

Prevention: Researchers are in the process of developing vaccines for several hemorrhagic viruses. A yellow fever vaccine is currently available for people traveling to areas where yellow fever is common.

If you live or work in an area where viral hemorrhagic diseases are common, you can do the following to reduce your risk:

  • Use proper protection, such as gloves, glasses, or a face shield, when working around people who have a virus.

  • Avoid being bitten by insects, especially mosquitos and ticks, by wearing protective clothing or using insect repellent.

  • Protect against rodent infestation by keeping food covered, removing garbage often, and making sure windows and doors are secured properly.

Neurologic Viral Diseases: Some viruses can infect the brain and surrounding tissues, causing Neurologic Viral Diseases. This can result in a range of symptoms, including:

  • fever

  • confusion

  • drowsiness

  • seizures

  • coordination problems

Examples of Neurologic Viral Diseases include:

  • Polio

  • Viral Meningitis

  • Viral Encephalitis

  • Rabies

  • Myalgic Encephalomyelitis (as per ICC-2011)

Treatment: There’s no specific treatment for people with mild viral meningitis or encephalitis. Getting plenty of rest, staying hydrated, and taking OTC anti-inflammatories to ease pain or headaches can all help. In some cases, antiviral medication may be prescribed. Polio or severe cases of meningitis or encephalitis may require additional treatment, such as breathing assistance or IV fluids. If an animal that’s suspected to have the rabies virus bites you, you’ll be given a series of shots to help prevent the rabies virus from infecting you.

Bottom line - science has only scratched the surface

There are many viral diseases. Some, such as the common cold or the stomach flu, are minor and go away on their own within a few days. Others, however, are more serious. Unlike bacterial infections, viral diseases don’t respond to antibiotics. Instead, treatment usually focuses on managing symptoms and supporting the immune system with plenty of rest and hydration.

What is Post Viral Fatigue? Fatigue is an overall feeling of tiredness or exhaustion. It’s completely normal to experience it from time to time. But sometimes it can linger for weeks or months after you’ve been sick with a viral infection, such as the flu. This is known as post-viral fatigue.

What causes post-viral fatigue? Post-viral fatigue seems to be triggered by a viral infection. In learning about your condition, you might come across information about Myalgic Encephalomyelitis. This is a complex condition that causes extreme tiredness for no clear reason. While some consider CFS and post-viral fatigue to be the same thing, post-viral fatigue has an identifiable underlying cause (a viral infection). Some viruses that seem to sometimes cause post-viral fatigue include:

  • Epstein-Barr virus

  • Human herpes virus 6

  • Human Immunodeficiency Virus

  • Enterovirus

  • Rubella

  • West Nile virus

  • Ross River virus

  • Dengue Fever virus

Experts aren’t sure why some viruses lead to post-viral fatigue, but it may be related to:

  • an unusual response to viruses that can remain latent within your body

  • increased levels of pro-inflammatory cytokines, which promote inflammation

  • nervous tissue inflammation

Laboratory diagnosis of viral infections

A wide variety of samples can be used for virological testing. The type of sample sent to the laboratory often depends on the type of viral infection being diagnosed and the test required. Proper sampling technique is essential to avoid potential pre-analytical errors. For example, different types of samples must be collected in appropriate tubes to maintain the integrity of the sample and stored at appropriate temperatures (usually 4°C) to preserve the virus and prevent bacterial or fungal growth. Sometimes multiple sites may also be sampled.

Types of samples include:

  • Blood

  • Skin

  • Sputum, gargles and bronchial washings

  • Urine

  • Semen

  • Faeces

  • Cerebrospinal fluid

  • Tissues (biopsies or post-mortem)

  • Dried blood spots​

Viruses are often isolated from the initial patient sample. This allows the virus sample to be grown into larger quantities and allows a larger number to tests to be run on them. This is particularly important for samples that contain new or rare viruses for which diagnostic tests are not yet developed.

For more information on Viruses:


Human Viruses Table: https://viralzone.expasy.org/678

The 9 Deadliest Viruses on Earth: https://www.livescience.com/56598-deadliest-viruses-on-earth.html

Classification of Viruses: https://www.google.com/search?rlz=1C1CHBF_enCA880CA880&sxsrf=ACYBGNRzCL4rJ60NG21Q9rrtpm1WKQ-e0g:1578416605535&q=classification+of+viruses&sa=X&ved=2ahUKEwiThdKI_PHmAhVGCM0KHfPqD40Q1QIoAHoECBUQAQ&biw=1296&bih=571

Viruses — Open Access Journal https://www.mdpi.com/journal/viruses

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