Take the 2-minute tour ×
Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. It's 100% free, no registration required.

I'm undergraduate physics student, but I've always been interested in biology. So I have a couple of questions about an application of the evolutionary principles to practice.

  1. Agony as the last stage of dying.
  2. Hydrophobia as symptom during Rabies.

Now I'm going to clarify what exactly I do not understand. In the first case it's not clear for me how this mechanism helps to survive, how it can help at all? In the second case it's not obvious why this virus causes such a symptom. As I think virus always create favorable environment for himselve (for reproduction). But how could water prevent it?

share|improve this question
4  
These might be better posed as separate questions. –  kmm Mar 17 '13 at 14:51
2  
I'm with Kevin. These seem like separate questions. To give you an idea of the first - Evolution via Natural Selection doesn't really 'care' how you die, as long as you've passed on your genes (reproduced) beforehand. –  MCM Mar 17 '13 at 20:28
2  
Agony is not always associated with the last stage of death, many pass peacefully - and the agony when it does occur is likely to be caused by the cause of death (ie a symptom) and possible exacerbated by the fact the person knows they are dying... And viruses/disease can have weird side effects on neural pathways which could be why we suffer from unusual neural episodes/behaviors –  GriffinEvo Mar 17 '13 at 21:05
    
Maybe you mean fear of death? I don't see that agony always accompanies death. Could you cite some reference or example? –  shigeta Mar 17 '13 at 22:30
add comment

1 Answer 1

The hydrophobia symptom is most likely a bi-product of the effects the virus has on the brain and not an evolutionarily derived strategy to create an appropriate environment to reproduce in. Just the same as other symptoms the infection causes, like fever for example, is a reaction the body has to the presence of the virus and not something the virus is doing on purpose to set up a better environment.

A bit old, but check out [1]: "Hydrophobia may represent an exaggerated respiratory tract irritant reflex with associated arousal potentiated by the selective destruction of brain stem inhibitory systmes."

So basically the virus is indirectly causing a fear of water. The destruction of brain cells and inflammation caused by the presence of the virus in the central nervous system cause a reflex in the respiratory tract which manifests as muscle spasms and renders the patient, who is already pretty out of it at this stage, unable and very unwilling to drink any fluids [2].

[1] http://europepmc.org/abstract/MED/982512 (Warrell DA, Transactions of the Royal Society of Tropical Medicine and Hygiene [1976, 70(3):188-195])

[2] http://publichealth.lacounty.gov/vet/rabiesmanual/clinical.htm

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.