[another_someone]

quote:Originally posted by Rokitansky
I have a thing on my mind. In case of heart cells, don`t you think that it is an inflamatory reaction that causes trouble, at least in some cases? I don`t realy know, i should study about it in a few months.
One more thing. Are you maybe a doctor or medical student ?
Thanks in advance.

My own feeling is that there are very many cases of disease, particularly viral disease, where the infectious agent is totally harmless, but it is only the host response that is damaging.

This would make some evolutionary sense.  From the point of view of a virus, it wants to be able to use the host to reproduce, and a dead host is not going to reproduce viruses.  On the other hand, a host is trying to maintain the purity of its DNA, and does not want to be reproducing alien DNA; so it is logical for a host to try and destroy infected cells as a means of quarantining the alien intruder.  In the extreme case, it might even be valid for an entire multicellular organism to commit suicide in order to protect its children and siblings from infection.

[ranganr]

Virus take up the control over protein formation machinery of human body cells once inside and these protein machinery now instead of forming human proteins produce viral proteins. Thus viral proteins formed unite to form a new viral particle. The human dead cell now busts and releases new viral particles.

[yellowcat]

How viruses cause disease is an interesting and complex topic
Viral virulence depends on many factors and you you cannot readily compare virulence of different viruses as symptoms can vary so much. For example you cannot say that rabies is more virulent than, Ebola or vice versa because the way you measure virulence in the two is  different,  attempts to say which is the most virulent virus are very
problematic.


Some viruses, enter at mucosal surfaces and  replicate in the epithelium.
Some viruses like HPV stay there and cause disease there, but others like spread
somewhere else like the CNS or the kidney where they cause disease.

One expression of viral virulence is tissue damage. Some viruses are cytopathic, they kill cells, they take over the host cell molecular processes like nucleic acid synthesis and protein synthesis that probably contributes to killing cells. Damaged cells  may undergo apoptosis or may be detected by the immune system that sends killer cells to take them out.

Some viruses lead to syncytium formation, that is multiple cell fusions resulting in
large multi-nucleated cells.


In many non-cytolytic virus infections, there is not a lot of virus induced tissue damage.
Rhinoviruses which cause around half of all the common colds, there is not much direct viral tissue damage observed, the virus really doesn't seem to kill the cells.
So the pathology of the infection is due to something else, that is your immune response to virus infection.

This is known as immunopathology, you need an immune response to clear the infection, but you pay a price in clinical symptoms, fever, tissue damage, aches, pains, nausea.
The virus itself is not damaging you so you feel pain, it's your immune response, your cytokines that cause your fever and the nausea.

One of the reasons suspected for the seriousness of avian flu is that birds have a naturally higher body temperature so the virus comes pre adapted to cope with the temperatures of our fever response, when the immune system continues to detect virus more cytokines are produced. This cytokine cascade also triggers rapidly proliferating and highly activated T-cells or natural killer (NK) cells that kill infected cells. If uncontrolled the damage produced by the immune response may be fatal.
http://www.ncbi.nlm.nih.gov/pubmed/1883518?dopt=Abstract&holding=npg
http://www.ncbi.nlm.nih.gov/pubmed/2364437?dopt=Abstract&holding=npg
http://www.ncbi.nlm.nih.gov/pubmed/12480361?dopt=Abstract&holding=npg
http://chemport.cas.org/cgi-bin/sdcgi?APP=ftslink&action=reflink&origin=npg&version=1.0&coi=1:STN:280:DC%2BD2Mnotlygtg%3D%3D&pissn=0818-9641&pyear=2007&md5=e1805470d7fe1b4e173c03b197df9e5d

There is a great deal more to this and it would probably take several volumes to cover it in depth.