Viruses are extremely small living organisms, invisible to the naked eye, and are among the most common causes of infectious diseases. They are also known as viruses and infect all types of living organisms, from humans and animals to plants and even bacteria. Millions of viruses exist, but only about five thousand are fully described. Viruses inhabit all ecosystems on Earth; in fact, they are the most abundant living organisms in nature. The first virus discovered was the tobacco mosaic virus. Viruses have various shapes, ranging from simple to spiral to very complex. They are transmitted through infection in several ways: via insects, through the air we breathe, through direct contact, through food or water, or through contaminated needles and blood transfusions.

Characteristics of Viruses

Viruses possess several characteristics, including:

They cannot reproduce or carry out their vital activity except within the cells of living organisms. Outside of living cells, they become inanimate.

Viruses are unaffected by antibiotics.

When present outside the cells of living organisms, they crystallize and are unaffected by environmental conditions.

They die at high temperatures.

They are very precise and selective; each type of virus is specific to certain cells.

They can mutate and change, producing new strains that the body's antibodies cannot recognize.

They spread very quickly; that is, they are highly contagious.

The Most Dangerous Types of Viruses

There are many dangerous viruses, but some cause certain and rapid death. Among the most dangerous of these viruses are:

Marburg virus: This dangerous virus causes hemorrhagic fever, and the condition can worsen, causing bleeding throughout the body, which leads to death. It was discovered in 1967.

Ebola virus: One of the most dangerous viruses ever, discovered in 2014.

Rabies: A virus that infects both domestic animals and humans, transmitted to humans from animals. It was first discovered in humans in 1920.

HIV: This virus tops the list of the most deadly diseases, destroying the body's immune system. It was first discovered in 1980.

Hantavirus: A very dangerous virus that affects the lungs, causing shortness of breath and often death. It was discovered in 1993.

Dengue fever: First discovered in 1950, it causes severe diarrhea in children.