30 January 2006

Chikungunya puts virology in perspective

Chikungunya virus in Reunion

This reminded me that some day the research we do will have a use. Chikungunya is related to Sindbis, which I work on. The currently infected people will have to suffer it though. How did we let mosquitoes hang out for so long?


visitor said...

Hi Ranjit,

How do new diseases (organisms) evolve? Were they already existing in nature (on some other organisms)? How did they suddenly become infective on man?

Is it too many questions?

Mosilager said...

hi visitor,
no not at all, fire away questions, I will try to answer them according to my expertise.

Definition of a new species is one that cannot reproduce successfully with a member of the old species. By this definition, tigers and lions are different species. They can mate and produce ligers, however these ligers cannot themselves produce any offspring. Same for horse and donkey (mule). Dogs and wolves are the same species by this definition as they can mate and produce viable offspring that can mate with each other.

The mechanism is usually explained by isolation of a population of the species from the rest followed by genetic mutations that do not allow cross-breeding. This occurs on a vast timescale so we cannot actually detect it happening so it is still a theory as far as I know.

The same thing applies to disease causing organisms. Thus far, we know that life only came into being once on Earth, and every creature is descended from that. The evidence for that is that the language of the nucleic acid (DNA or RNA) is the same for every organism.

I don't know too much about bacterial diseases, but the general consensus is that the misuse of antibiotics has led to the development of bacteria that are resistant to many antibiotics. The problem is that people don't take the entire round of antibiotics, which allows a few bacteria to survive. People normally stop taking antibiotics when they start to feel better, but this is a bad practice because the bacteria that were not killed now can tolerate a higher dose of the antibiotic. In some cases there are mutations in genes that cause the bacteria to be resistant to the antibiotic. Of course these bacteria would outgrow the rest in the presence of the antibiotic. Other ways are for the bacteria to pick up a piece of DNA from its environment that gives it resistance. Either way, T.B. has come back due to these mechanisms and some are resistant to most drugs on the market. Drug companies do not do research on producing new antibiotics because it is not profitable enough.

If you are talking about viruses like HIV, it probably came from an older virus that changed slightly and was now able to infect people (our mutation leading to a new organism theory). Ebola probably has certain animals that can carry it without being sick themselves and when people come in contact with it they get exposed. We were able to eradicate smallpox because it only grew in humans and not in any other creatures. We could also eradicate polio if everyone would take their vaccine due to the same reasons!

So different reasons... the thing to understand is that the vast majority of bacteria and viruses do not cause disease. It's a very small minority that does, and again a small minority of them make you sick enough to feel bad.

Hope that wasn't too technical... let me know if you have more questions.

The Visitor said...

Thanks Ranjit, for that lucid explanation, it did clear my doubts. And the explanation wasn't too technical for me :)

Mosilager said...

cool, nice to be able to share some of the tidbits I've picked up in the field :)