Health virus information

Some are additionally enveloped in a soft, lipid wrapping. These tiny virus packages are just tens to a few hundreds of nanometers across. This makes them smaller than most bacteria, which can be a small as roughly a tenth the size of a human blood cell.

Such a tiny size means that you can't even spot most viruses with a light microscope. The one exception, a group known as giant viruses , has members with astonishingly large genomes.

These mega-viruses are hundreds of times larger than most, with capsids that span roughly to nanometers across and full viral forms that can measure up to nanometers across. Due to their simple structure, viruses cannot move or even reproduce without the help of an unwitting host cell. But when it finds a host, a virus can multiply and spread rapidly.

To identify the correct host, viruses have evolved receptors on their surfaces that match up with those of their ideal target cell, letting the virus get its genetic material inside and hijack its host's cellular machinery to help it reproduce by multiplying the virus' genetic material and proteins. Using that strategy, the minute marauders have flourished and evolved in step with their hosts. By one estimate , at least , different viruses can infect mammals alone, and even this massive number may be on the low side.

This viral army can cause symptoms as mild as a cough or as deadly as internal bleeding. Some viruses may even cause the runaway cellular growth that is the root of cancer, as is thought to be the case with human papillomavirus and cervical cancer. Inside their cellular hosts, viruses can create an enormous number of copies and spread the infection to other cells. For example, if you get the flu, your body will be riddled with some hundred trillion viruses in just a few days —more than 10, times the number of people on Earth.

How viruses spread from person to person depends on the type. Many hitch a ride in the mist of droplets that flies from your mouth every time you cough or sneeze. A variety of factors can influence how fast these airborne viruses can spread. Flu, for one, seems to survive longer in cool, dry environments , which may be the source of its common winter spread.

But in tropical regions, high humidity seems to help the flu jump from person to person. Other viruses spread most easily through contact with other bodily fluids. For example, Ebola virus spreads from contact with infected blood, feces, or vomit. Unlike many other viruses, scientists think Ebola cannot spread through the air after people with the virus cough or sneeze.

Still other viruses travel through an intermediary, like a mosquito, which then infects people by biting them. One example of these so-called mosquito-born diseases is dengue, which causes a potentially deadly flu-like infection.

The risk of dengue has risen in recent years, currently threatening roughly half of the global population, according to the World Health Organization. Other notorious mosquito-born diseases include Zika, Chikungunya, and West Nile. Skip directly to site content Skip directly to page options Skip directly to A-Z link. Section Navigation. Facebook Twitter LinkedIn Syndicate. Minus Related Pages. Know the symptoms to look for and how to care for people with RSV. Start Here. Bacterial vs.

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