Are viruses tissue specific? Is this why a virus may cause a stomach ache or a sore throat or a lung infection?
How do viruses actually harm you? Is it because they burst the cells open when they reproduce or are there other mechanisms?
Thanks
Viruses can certainly only affect specific types of tissues. The HIV virus only affects human T-cells because of the way it attaches to the proteins on the surface of the cells.
Viruses often destroy the cells that they infect, but it is possible for some viruses to infect a cell and have the cell still function more or less normally. This is how some viruses can lay dormant in a person for extended periods of time before becoming active.
The wikipedia page on viruses has a lot of good info:
I looked through that most excellent Wiki entry but did not find reference to a question my wife posed the other day: are any viruses beneficial? I see that the term, virus, refers to something that causes disease, something virulent, but aside from their function in aquatic environments, I found nothing to suggest positive effects of viruses. And some viruses have been employed in research and gene therapy. As we know, there are good and bad bacteria - at least as far as our functioning is concerned. In that regard, are there any good viruses?
If you get certain fairly harmless viruses you build up antibodies against other viruses in the same class that may be much more harmful. For example, if you catch cowpox you end up immune to smallpox. That’s how Edward Jenner figured out how to make the smallpox vaccine.
Yes, viruses exhibit what is known as ‘tissue tropism’; that is, some viruses preferentially (or exclusively) infect specific tissues. For example, papillomaviruses typically infect the basal keratinocytes of the skin, producing warts. Herpesviruses like to infect neurons where they can undergo a latent cycle. When you are under stress, these viruses can reactivate and migrate from the facial nerves to the surface of the skin where they produce what are commonly known as cold sores. Flu viruses (orthomyxoviruses) usually infect the upper respiratory tract.
Viruses can produce symptoms by the direct action of cell lysis (bursting) or through production of toxins. HIV, a retrovirus, produces the AIDS symptoms because it lyses your T cells, essential components of the human immune system. However, more often and like many other pathological agents, it is essentially your own body that is producing many of the symptoms to the disease. As an example, the cell lysis produced by dengue virus doesn’t really produce many symptoms. It is, however, your immune system’s overactive response to the viral particles that can lead to shock, hemorrhage, and death.
Are there any ‘beneficial’ viruses? Modern bioengineering is currently working on a number of cancer and gene therapies. Reoviruses and adenoviruses have been investigated into their potential as cancer therapy agents, because they preferentially infect cancer cells. Adenoviruses in particular are also thought to be a good vector for gene therapy or targeting of chemical therapies. Herpesviruses undergo a latent stage where they are not actively replicating, but have been observed to increase the hosts’ IFN-gamma and TNF-alpha levels, two important immune modulators. This makes it so your immune systems macrophages, the foot soldiers, are primed and ready to repel other microbial invaders, like Listeria and Yersinia (causative agent of the Plague).
None that have been discovered yet. Viruses are purely parasitic in nature.
I heard some scuttlebut in Norwegian medias that some relatively harmless viruses were used to distribute medicine in genetics experiments. That is, they piggybacked the good stuff on a dormant/empty virus and injected the test animal with it, so it could affect the cells on a genetic level. (This is all half-remembered from about four years ago, can anyone recall seeing the story?)
I think that in this case the virus would not be seen as “good”, but rather “not bad”. The virus itself is not beneficial; the best that can be said for it is that it is non-disruptive to its host, allowing it to be used for a “good” purpose.
You could certainly have a virus which didn’t affect humans directly, but which attacked some other organism which is itself harmful. I think you could call that a “good virus”.
They can be helpful to other viruses.
Hepatitis D is an extremely small virus that doesn’t even contain the DNA for a protein coat, it can only replicate in the presence of Hepatitis B infections and it basically hijacks the other viruses shell proteins Grand Theft Genome style.
I’m pretty sure I’ve also seen it suggested that the random cutting and pasting of DNA that viruses tend to do has had a significant impact on evolution.
The use of bacteriaphages which are viruses which attack bacteria is (or was) a promising alternative to treating resistant forms of bacterial infections. I believe pioneered in the former soviet satellite of Georgia.