Many human illnesses are caused by viruses. We’re even now learning that many forms of cancer originate from viruses.

What is a virus?
Viruses are sort of like zombies. They’re not alive; they do not have cells, they can’t turn food into energy, and without a host they are just inert packets of RNA chemicals. Yet they’re not exactly dead, either. They have genes, they do reproduce, and they evolve through natural selection just like all other life on Earth.

Viruses are much smaller than bacteria but far more numerous than all other life forms on Earth combined. Viruses are known to infect animals, plants, fungi, protozoa, archaea, and bacteria. Recent research has indicated they might even infect each other.

Why are viral infections so dangerous?
Although most viruses are benign and not harmful, a couple things make viral infections especially nasty. First, viruses utilize cellular integration–hiding within their hosts own cells, which makes them harder to kill. They also replicate at astonishingly high rates, so they can multiply quickly, leaving your immune system one step behind. Both of these things make total eradication especially hard, so antivirals instead try to limit the infection to low levels that cannot hurt the body. Which is why antivirals can keep HIV patients healthy but we can’t as of yet completely eradicate the virus from the body.

See also:

Virus facts and statistics

Types of viruses & viral infections

Viruses come in all different types and varieties. Here are some of the more notable viral diseases:

  • Influenza (Flu)
  • Coronavirus
  • HIV/AIDS
  • Herpes
  • Human papilloma virus (HPV)
  • Rabies
  • Zika virus
  • Malaria
  • How do viruses spread?

Viruses spread in all the typical fashions: through touch, through the exchange of bodily fluids, or through the air, though the particular means of transmission can vary by the type of virus. Viruses are typically spread when kids sneeze and cough, sending live airborne viruses that are then inhaled by those nearby. They can also be spread indirectly through physical contact or by touching a contaminated surface.

Viruses can live on outdoor equipment anywhere from a few minutes to a couple of days. They can be transferred when a child touches an infected surface and then touches his eyes, mouth, or nose to introduce the virus into the body, which is why hand-washing and keeping kids from touching their face or putting hands in their mouth can limit the spread of viruses.

“Like any other poison, viruses are usually more dangerous in larger amounts,” says Professor Joshua Rabinowitz and research fellow Caroline Bartman. “Small initial exposures tend to lead to mild or asymptomatic infections, while larger doses can be lethal.” This means how sick you end up can depend on whether you were infected by touching a contaminated surface versus living with someone who was constantly exhaling these viruses into the air as you breathe.

The reason initial exposure can matter so much is that viruses start multiplying quickly once they’ve entered the body, so it’s a race against the immune system to try and kill the infection. An infection that starts with 100 viral agents that began multiplying exponentially can be very different from an infection that starts with 10,000 viral agents that begin multiplying exponentially. In both human and animal studies, subjects with low dose virus exposures recover quickly with fewer visible symptoms, while subjects with higher dose initial exposures get more sick.