Viruses are microscopic organisms that are present everywhere on earth. They can infect humans, animals, plants, fungi, and even bacteria. Sometimes a virus can cause deadly diseases resulting in the death of the organism.
Other viral infections do not trigger any noticeable reactions. Viruses have different effects on different organisms.
Viruses differ in complexity. They comprise of genetic material, RNA or DNA which are surrounded by a coat of protein, lipid (fat), or glycoprotein. They cannot replicate without a host hence can be classified as parasitic.
Viruses are considered to be the most abundant biological entity on the planet. They exist in a form known as virions, before entering a cell.
Viruses exist in different shapes and sizes and are categorized based on their shapes. Some of the common shapes of viruses are helical, envelope, and icosahedral or near-spherical viruses.
Sources of Virus:
Viruses are difficult to trace through time as do not leave fossil remains. Molecular techniques are followed to compare the DNA and RNA of viruses and learn more about where they come from. Read the oncology journal for information on tumors.
Three competing theories that try to explain the origin of viruses.
- Virus-First Hypothesis: Viruses had evolved from complex molecules of nucleic acid and proteins before or at the same time as the first cells appeared on the planet, billions of years ago.
- Regressive, or Reduction Hypothesis: Viruses first existed as independent organisms that later became parasites. With time, they shed genes that did not allow them to parasitize, and they became completely dependent on the cells they inhabit.
- Progressive, or Escape Hypothesis: Viruses have evolved from sections of DNA or RNA that broke free from the genes of larger organisms. They became capable of being independent and move between cells in this way.
Diseases caused by Viruses:
- Common cold and different types of flu
- Measles, mumps, rubella, chicken pox, and shingles
- herpes and cold sores
- Severe acute respiratory syndrome (SARS)
- Ebola and Hanta fever
- HIV, the virus that causes AIDS
- Dengue fever, Zika, and Epstein-Barr
- Some viruses, like the human papillomavirus (HPV), may lead to cancer.
How Are Viruses Transmitted?
A virus exists only to reproduce, and when it reproduces, its offspring spreads to new cells and hosts. The ability of a virus to spread depends on what it is made of. Viruses transmit from person to person, and from mother to its fetus during pregnancy or delivery.
They can also spread through:
- Exchanges of saliva
- Sexual contact
- Coughing, or sneezing
- Insects that carry viruses from one person to another
- Contaminated food or water
Some viruses tend to live on an object for some time, so if a person touches something with the virus on their hands, the next person who touches the same object can pick that virus up.
This object is known as a fomite. The virus starts to affect the host as it replicates in the body. After a period generally known as the incubation period, symptoms might begin to show.
Types of Viruses
There are various types of viruses that have different effects on humans and other organisms and cause diseases or illnesses.
- Some of the common types of viruses are:
- Cold viruses
- Flu viruses
- Hepatitis viruses
- Stomach and intestinal viruses
- Other Human viruses. You can read more in the virology journal.