Viruses can infect all types of life forms, from animals and plants to bacteria and archaea.
Since Dmitri Ivanovsky's 1892 article describing a non-bacterial pathogen infecting tobacco plants, and the discovery of the tobacco mosaic virus by Martinus Beijerinck in 1898, about 5,000 viruses have been described in detail, although there are millions of different types. Viruses are found in almost every ecosystem on Earth and are the most abundant type of biological entity. The study of viruses is known as virology, a sub-speciality of microbiology.
Virus particles (known as virions) consist of two or three parts: i) the genetic material made from either DNA or RNA, long molecules that carry genetic information; ii) a protein coat that protects these genes; and in some cases iii) an envelope of lipids that surrounds the protein coat when they are outside a cell. The shapes of viruses range from simple helical and icosahedral forms to more complex structures. The average virus is about one one-hundredth the size of the average bacterium. Most viruses are too small to be seen directly with an optical microscope.
The origins of viruses in the evolutionary history of life are unclear: some may have evolved from plasmids—pieces of DNA that can move between cells—while others may have evolved from bacteria. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity. Viruses are considered by some to be a life form, because they carry genetic material, reproduce, and evolve through natural selection. However they lack key characteristics (such as cell structure) that are generally considered necessary to count as life. Because they possess some but not all such qualities, viruses have been described as "organisms at the edge of life".
Viruses spread in many ways; viruses in plants are often transmitted from plant to plant by insects that feed on plant sap, such as aphids; viruses in animals can be carried by blood-sucking insects. These disease-bearing organisms are known as vectors. Influenza viruses are spread by coughing and sneezing. Norovirus and rotavirus, common causes of viral gastroenteritis, are transmitted by the faecal–oral route and are passed from person to person by contact, entering the body in food or water. HIV is one of several viruses transmitted through sexual contact and by exposure to infected blood. The range of host cells that a virus can infect is called its "host range". This can be narrow or, as when a virus is capable of infecting many species, broad.
Viral infections in animals provoke an immune response that usually eliminates the infecting virus. Immune responses can also be produced by vaccines, which confer an artificially acquired immunity to the specific viral infection. However, some viruses including those that cause AIDS and viral hepatitis evade these immune responses and result in chronic infections. Antibiotics have no effect on viruses, but several antiviral drugs have been developed.
What was fake on the Internet this week: Ebola edition. An Ebola nurse in Germany.
(Reuters/Ralph Orlowski) There is so much fake stuff on the Internet in any given week that we’ve grown tired of debunking it all. Fake Twitter fights. Fake pumpkin-spice products. Amazing viral video? So, rather than take down each and every undeservedly viral story that crosses our monitors each week, we’re rounding them all up in a quick, once-a-week Friday debunk of fake photos, misleading headlines and bad studies that you probably shouldn’t share over the weekend.
Ready? 1. Yes, some tweeter in Alaska did cleverly Photoshop a page to make it look as though there was an outbreak at an Anchorage High School. 2. 3. 4. 5. Don’t Worry, Be Rational: Why Extreme Fear Of Ebola Is Bad For Your Health. A licensed clinician participates in a CDC training course in Alabama earlier this month for treating Ebola patients.
(Brynn Anderson/AP) Let’s face it, Ebola is scary. My kids are scared. The moms at school are talking about giving their children extra multi-vitamins to boost their immune systems in a desperate attempt to do something, anything, to protect their families. But we live in Boston and there are no cases here — yet. So, in a crisis, who do you call for comfort? Here, edited, is our short interview: RZ: So, why is being scared of Ebola bad for your health? DR: The health ramifications of this are profound.
[The negative effects of chronic stress are widely reported, but Ropeik cites the book "Why Zebras Don't Get Ulcers," by the biologist Robert Sapolsky, as a key source here.] So you think people are overreacting and we’re moving into some kind of widespread nation-wide chronic stress phenomenon here? We’re on the cusp. Virus. Etymology.
Origins. Microbiology. Ebola. Dog Thoughts That Will Change Your Outlook On Everyday Dog Life.