[neilep (OP)]

Viruses are well naughty aren't they ?   They can make you sick and even worse !


What about good positive viruses ? do they exist ? if not, why not ?

[Colin2B]

What about good positive viruses ? do they exist ? if not, why not ?

Apparently they do:
The polydnaviruses of endoparasitoid wasps have evolved with their hosts to become essential. Many of the viral genes are now encoded in the host nucleus.

Endogenous retroviruses are abundant in many genomes of higher eukaryotes, and some have been involved in the evolution of their hosts, such as placental mammals.

Some mammalian viruses can protect their hosts from infection by related viruses or from disease caused by completely unrelated pathogens, such as bubonic plague.

Viruses can protect their hosts by killing off competitors, as is seen with the killer viruses in yeasts.

A fungal virus confers thermal tolerance to a plant in a complex symbiosis involving its fungal host and the plant that the fungus colonizes.

Several acute plant viruses confer conditional mutualism by enhancing drought tolerance in plants.

Insect viruses have numerous mutualistic relationships with their hosts; in addition, viruses play parts in bacterium–insect mutualisms.

Also they are now being used in medicine to carry treatments and gene editing.

[neilep (OP)]

What about good positive viruses ? do they exist ? if not, why not ?

Apparently they do:
The polydnaviruses of endoparasitoid wasps have evolved with their hosts to become essential. Many of the viral genes are now encoded in the host nucleus.

Thank ewe Colin,

This is fascinating, the host must have evolved a defence then turned it into an advantage.   I appreciate your answer.

[Colin2B]

....the host must have evolved a defence then turned it into an advantage.   I appreciate your answer.

It’s possible there never was a threat. Like bacteria, we only tend to hear about the nasty ones, but now we are learning a lot about the importance to our health of gut bacteria, skin bacteria etc.
At the end of the day, the human body is a colony of cooperative cells and organisms - if you are useful, welcome.

[neilep (OP)]

....the host must have evolved a defence then turned it into an advantage.   I appreciate your answer.

It’s possible there never was a threat. Like bacteria, we only tend to hear about the nasty ones, but now we are learning a lot about the importance to our health of gut bacteria, skin bacteria etc.
At the end of the day, the human body is a colony of cooperative cells and organisms - if you are useful, welcome.

This just goes to prove that ewe are truly never alone !  ;-)

[alancalverd]

If you are an invading  grey squirrel, squirrelpox is very good at eliminating your native competitors, just as smallpox helped destroy civilisation in the USA.

[Bored chemist]

There are viruses that prey on bacteria which may be useful.
https://en.wikipedia.org/wiki/Phage_therapy

My enemy's enemy is my friend. :-)

[evan_au]

Are There Any GOOD Viruses ?

These little viruses attack bacteria - which is a good thing if the bacterium is something that attacks us...
https://en.wikipedia.org/wiki/Bacteriophage

The enemy of my enemy is my friend

Oops! Bored Chemist just beat me to it!

[Edwina Lee]

And there are the flesh eating bacteria + phage attack.
I guess without the phage, the bacteria is not deadly.

[Bored chemist]

And there are the flesh eating bacteria + phage attack.

How?
Phages attack bacteria, not human cells.

[alancalverd]

Tobacco mosaic virus helps maintain the cost of smoking and thus saves lives.