Cholera, bubonic plague, smallpox, and influenza are some of the most brutal killers in human history. And outbreaks of these diseases across international borders, are properly defined as pandemic, especially smallpox, which throughout history, has killed between 300-500 million people in its 12,000 year existence.
Two scientists contributed to the discovery of the first virus, Tobacco mosaic virus. Ivanoski reported in 1892 that extracts from infected leaves were still infectious after filtration through a Chamberland filter-candle.
Scientists believe they are at least as old as the first cells, which emerged around 4 billion years ago, but viruses could be even older, existing in the precellular world as self-replicating entities that subsequently evolved into forms that parasitize other cells.
Adenovirus is the smallest virus and Mycoplasma is the smallest bacteria. Both bacteria and viruses are contagious organisms that lead to many diseases in both plants and animals.
Viruses may have arisen from mobile genetic elements that gained the ability to move between cells. They may be descendants of previously free-living organisms that adapted a parasitic replication strategy. Perhaps viruses existed before, and led to the evolution of, cellular life.
Tobacco mosaic virus
Abstract. Two scientists contributed to the discovery of the first virus, Tobacco mosaic virus. Ivanoski reported in 1892 that extracts from infected leaves were still infectious after filtration through a Chamberland filter-candle.
Virus-first hypothesis: Viruses evolved from complex molecules of protein and nucleic acid before cells first appeared on earth. By this hypothesis, viruses contributed to the rise of cellular life. This is supported by the idea that all viral genomes encode proteins that do not have cellular homologs.
The physically largest virus is Pithovirus sibericum, at 1.5 microns (or 1,500 nanometers) in length . Though that might seem tiny, it is larger than some bacteria, and approximately half the width of a strand of spider web silk .
Viruses are the smallest of all the microbes. They are said to be so small that 500 million rhinoviruses (which cause the common cold) could fit on to the head of a pin. They are unique because they are only alive and able to multiply inside the cells of other living things.
3.6 billion years old
Over time, they adapted themselves to new hosts. The researchers cannot directly detect such old viruses. The oldest evidence of bacteria can be found, for example, in so-called stromatolites, the oldest of which are 3.6 billion years old and were found in Australia. A direct proof of ancient viruses is not known.
In fact, his family tree suggests viruses and bacteria share a common ancestor – a fully functioning, self-replicating cell that lived around 3.4 billion years ago, shortly after life first emerged on the planet.
Dmitri Ivanowsky in 1892. He recognized an infectious agent, which caused tobacco mosaic disease and were smaller than bacteria. M.W. Beijerinek in 1898 called the filter 'Contagium vivum fluidum' and named it the 'virus'.
Huge genome allows mimivirus to make its own proteins.
This monster has just had its genome sequenced, and scientists say that, unlike its fellow viruses, it may truly be called 'alive'.
Mimivirus is the largest virus ever discovered. Giant viruses had been known for a few years, many of them in a group termed nucleo-cytoplasmic large DNA viruses (NCLDVs).
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Viral infections can cause serious complications, both shortly after getting sick or years later. Complications include: Inflammation in your lungs (pneumonia). Respiratory illnesses can infect your lungs and cause swelling that can make it hard to breathe.
As noted by Discovery, the Creeper program, often regarded as the first virus, was created in 1971 by Bob Thomas of BBN. Creeper was actually designed as a security test to see if a self-replicating program was possible.
Research on viruses has been recognized with several Nobel Prizes. Viruses attack both animals and plants. Tobacco plants are damaged sometimes with mosaic-like patterns on the leaves. These patterns are caused by the tobacco mosaic virus, which at the end of the 19th century became the first virus ever discovered.
The first evidence of the existence of viruses came from experiments with filters that had pores small enough to retain bacteria. In 1892, Dmitri Ivanovsky used one of these filters to show that sap from a diseased tobacco plant remained infectious to healthy tobacco plants despite having been filtered.
These massive parasites were considered rare at the time, but they've since proved more common than anyone expected. Now, researchers have found entire giant virus genomes embedded in the genomes of several common algae.
The good news is that it's astronomically implausible. “We've had only two or three instances in my lifetime that could be even remotely comparable to Resident Evil's description of the t-Virus outbreak,” says Waterfield, “And they aren't even close. That's Ebola, SARS, and the various mutations of the influenza virus.
At 680 nm in diameter, Megavirus is slightly smaller than Mimivirus, but the DNA genome is larger – 1,259,197 base pairs versus 1,182,000. The Megavirus genome encodes 1,120 putative proteins compared with 979 for Mimivirus.
But some people may be infectious for up to 10 days. Symptoms in children and babies are milder than those in adults, and some infected kids may not show any signs of being unwell. People who experience more serious illness may take weeks to recover. Symptoms may continue for several weeks after infection.
Viral infections can vary a lot in how long they last, for instance: Respiratory infections can last a few days to two weeks. A wart on your skin can last for a year or longer. Hepatitis B and C can cause chronic infections that last for years.
We can find them everywhere, even in our own intestines: bacteriophages. These viruses infest bacteria and eliminate harmful ones in the process.