Hi, I'm Craig! I contracted the beauty virus, and this is Mental Floss on YouTube.

Today, I'm gonna answer acalibaby808's big question, "Are there good viruses?" Let's get started.

(Mental_Floss intro plays)

It turns out that virus doesn't necessarily mean "disease". In fact, there are actually trillions of viruses in our bodies, and they're not at all bad. A virus just is a microorganism that can only reproduce if it's in a living organism, and often, they're the cause of disease and disease spread, but some viruses might be good for us.

For centuries, people have found ways for viruses to be advantageous. For instance, in the 1700's, it was discovered that milkmaids who had a mild version of cowpox were immune to virulent smallpox. Because of this discovery, scientists were able to develop a smallpox vaccine with the vaccinia virus, which is related to the cowpox virus.

It's possible that viruses might be crucial to the development of healthy organs. In 2011, immunologist Ken Cadwell conducted an experiment to learn more about the microbiome: a group of about one hundred trillion microbes in our bodies. The microbiome has a lot of important roles, like aiding the development of intestines. And I love my intestines, both large and small.

Doctor Cadwell found that raising young mice in a completely sterile environment affected the microbiomes said that their intestines didn't develop normally. But, when he gave the mice a murine norovirus similar to the one that affects humans, their intestines and immune system developed normally.

That's the virus you get on a cruise ship, right? So, did he put the mice on a cruise ship? I don't wanna be on that cruise ship.

This study may apply to people, meaning exposure to viruses at a young age might be good for us. But Cadwell notes that viruses affect people differently, so it won't work the same way for everyone.

There are also viruses known as phages, found in our body's mucus, like in the mouth, nose, and digestive track--eww!--and phages actually kill unwanted bacteria. A 2013 study in The Proceedings of the National Academy of Scientists, or PNAS, found that when a phage was put with an E. coli bacterium in a culture, the phage was able to kill the bacteria.

Another interesting virus that's currently being studied is known as GB Virus-C (GBV-C). Over a billion people alive today have already been infected with it at some time in their lives. A few experiments suggest that when someone with HIV also gets infected with GBV-C, the spreading of HIV might decelerate. Some experts also believe that GBV-C might help a person survive Ebola, although there's not a lot of data on that at the moment.

Thanks for watching Mental Floss on YouTube, which is made with the help of all these nice viruses. If you have a big question of your own that you'd like answered, leave it below in the comments. See ya next week!