Earth Science: Viruses – Viruses As Pathogens
The term virus comes from Latin and means poison. As the name implies, viruses may cause serious disease, often with no possible treatment due to the lack of effective medication.
The influenza virus exists in varying strains, but the main strains that cause the flu result in symptoms that are very similar to those of the common cold. Fatigue and pain in the limbs, headaches, and occasionally high fevers are common. The human body, which is weakened due to the influenza virus, is therefore susceptible to sometimes fatal secondary infections, for example, due to bacteria.
Very infectious strains of this pathogen may cause flu epidemics. An example of such an epidemic is the Spanish flu of 1918 to 1920. It is estimated that 25 million people died from the flu during this time. Avian flu is another extremely contagious and aggressive strain that is caused by influenza viruses. Normally these pathogens are only passed on from one bird to another, but in recent years there have been cases of viruses infecting mammals too, including humans.
The human immunodeficiency virus (HIV)
Today one of the most feared viral diseases among humans is AIDS (acquired immune deficiency syndrome). It is an infection caused by the human immunodeficiency virus (HIV). The disease is almost always fatal. It is estimated that about 40 million people worldwide have been infected with the HIV virus or have fallen ill with AIDS. The HIV pathogen is a retrovirus; it carries its genetic information in a single strand of RNA rather than DNA, and has a particular enzyme called reverse transcriptase.
The enzyme is responsible for transcribing RNA into DNA during infection of a host cell. The transcribed DNA is then integrated into the genome of the host cell. This is followed by a sometimes lengthy latent period of inactivity. Once the virus becomes active it destroys important immune cells (T helper cells), which leads to a permanent deficiency of the immune system as a whole.
Patients often die from diseases that their immune system would have normally been able to defend against. Despite increased research efforts into the development of medication or effective vaccination to prevent the immune deficiency, a cure still has not been found.
REMBRANDT TULIPS
These tulips developed multicolored flowers that were extremely popular and valuable during the 17th century At the beginning of the 20th century the cause for the coloring was finally discovered: a virus prevented an even distribution of pigments.
Most Rembrandt tulips sold today are no longer infected with the virus, but they are produced by selective breeding
BASICS
THE FIRST vaccination against the smallpox virus may have been developed about 3,000 years ago.
There are accounts of Chinese healers who immunized patients with an inhalation of powder made from smallpox scabs of epidemic survivors.