david_x said:
No thats not true, the coloney that had the ability to defend against the treatment is actually weaker than the one that can't so that the one that can't defend will retake dominence.
Ok, are you talking about
viral strains or
bacterial colonies, we don't get viral colonies. ~I think I see where you are coming from, I have vague recollections of high school biology where on a petri dish I would grow two different types of bacteria, one with a mutation which makes it resistant to antibiotic, during treatment with antibiotic the resistant species grows and dominates, and the suscepitble species all but dies off, once the antibiotic has worn off the susceptible species can grow and sometimes will regain dominance over the petri dish.
Ok forget about that, that is not a model for viral infections, they work in a completely different manner, take the flu virus, you are walking along one day and you inhale a virus particle, it manages to invade a cell in your respiratory tract where it hijaks the cells DNA replicating machinery, the viral particle replicates inside the cell and eventually causes the cell to split releasing viral particles which go on to invade other cells. You with me?
Immunity to viral strains is acquired by this process, once inside the host cell the viral particle is presented to various immune cells called lymphocytes which have antibody on their surface, there are millions of such cells in our body all carrying a different antibody, eventually the viral particle will be presented to a lymphocyte which matches, like a lock and key, this causes a reaction inside the lymphocyte resulting in the production of antibody specific to the virus, the remaining virus particles present in the body are mopped up by antibody and the cells carrying virus are killed. Do you know why you get a sore throat when you have a bad cold? It isn't the virus which causes it, its' the immune response destroying all viral infected cells. You still with me?
When we have coughs and colds we tend to sneeze and cough alot, this results in the expulsion of viral particles from our body where they are passed to a different host and the whole cycle begins again. Over the course of a viral infection in a population it is passed from many hosts, and during replication inside the host cell mutations occur, if these mutations occur in the genes which code for viral coat protein then we end up with a new varient which our immune system doesn't recognise, this is the reason why the cough/cold viruses have not been wiped out, because it keeps mutating as it is passed around a population and it comes back to infect us again and again and again.
Vaccines to a virus work on a similar prinicple to acquired immunity, we are injected with a protein which resembles viral coat protein, our body mounts an immune response to it, which is relatively weak compared to a full blown infection, our bodies produce antibody to the vaccine and therefore upon subsequent infection with the virus proper we already have immunity. Unfortunatly immunity is short lived, the flu virus mutates very quickly and the immunisation we recieve in winter 2004 will not protect us against the flu virus doing the rounds in winter 2005.
I realise that's a lot to chew over, if you managed to understand it I'll be impressed, if you would like any further explanation I'm happy to oblige, I have a degree in Medical Microbiology, and therefore I have a fair grasp on things.
I'm sure you realize that a medicine does not entirly wipe out the population of even the susceptible viruses.
Yes it does, but viruses mutate, they're very good at it as it's one of their survival mechanisms.
I'm ahead of 98% of my class overall. In science i'm ahead of 99% of my class.
Honestly, I don't think so. I have worked with 17/18 year old high school kids who were in the 90th percentile and above, you don't have the level of understanding I would expect from a top performing student.
