[Shadec (OP)]

Joel Hillman  asked the Naked Scientists:
   
I was watching a great little sci-fi show a little while ago which had an eight-legged endoparasite, which once inside the body suspended the body's descent into senescence and extended the lifespan indefinitely.

While this is a little too far into the realms of fiction, I was wondering if there was any science to be found? I know there have been a few studies on helminth therapy and the like, that's not what I mean, but I was wondering - is there actually any truth in this?

It does make a vague sort of sense, if the parasite's host lives a longer life, with less disease and faster healing, better health etc surely this provides a very large benefit for the parasite? I mean if it lives off a host, and the host lives indefinitely - then this has a clear advantage.

Thanks very much

J

What do you think?

[imatfaal]

Joel - we already have a huge group of bacteria living in our guts, which make our lives possible not just longer.

[Shadec (OP)]

That's not actually parasitic, that's really more of a symbiotic relationship than a parasitic one, I would think. ie the bacterium benefit by having a share of the food, they have a place to live etc., but the body also digests some, and is given the opportunity to make use of certain substances which it might not have otherwise been able to, etc.

I know that many parasites don't kill their host, and I know that pretty much the definition of a parasite is that it gains at the expense of the host, but does anyone know about any parasites which provide a benefit their host, as well as being parasitic?
I also realise that this may push them more into the symbiotic relationship group, but the concept is still the same.

[imatfaal]

Shadec - how is it "still the same"?  I kinda see what you are driving at - but a parasite and a symbiot are distinguished by their relationship with the host.  If a parasite benefits the host - then they enter a commensal relationship with the host; the difference between a long term commensal parasite and a symbiot is very slight.  If you view symbiots as organisms that cannot live apart - then it becomes a very difficult question to experimentally answer.  In controlled experimental situations how can we remove the influence of gut flora from a healthy human without having to engage with huge ethical and potentially criminal matters?  Those who have lost gut flora due to illness or intervention are not a base from which we can judge. 

To answer your question - I do not know of an organism that humans can live very well without - but with which they will live better.  I think the reason is the immense amount of cross-breeding and intermingling of human society - anything that is so beneficial we already all share.  Would love to hear that this is incorrect as it is not my field - just my twopennneth

[SteveFish]

A simplistic answer. A parasite benefits at the expense of the host. A weak form of symbiosis exists when both the host and parasite benefit but the relationship is not necessary to either. This is a, sort of, mutual parasitism. Strong symbiosis is when both parties benefit and are both necessary in order for each to live.

[Shadec (OP)]

I suppose they aren't really the same, and I guess that does push it into commensalism, but what you said about living without, but being benefited if it's there.

The reason I said parasite was that I specifically meant in a parasitic kind of setting, ie not a cleaner wrasse and a shark, where the two can live apart, and not like lichen, where they are dependent upon each other to live, but something that specifically offers a trade - living as a parasite, while extending the lifespan or some such. My own (somewhat pale, in comparison with others I imagine are on here) knowledge of medicine and biological sciences say that there isn't a clear method or path for this to occur, I mean I, for one, cannot see a clear way that an organism could do this, but it does seem logical for it to happen. I'm not necessarily saying that it does, just that it would kinda make sense if it did.
The reason that I ask, despite this is that my knowledge of the world, much to my dismay, is not complete, and thus I must ask other members of the scientific community for help.

I guess my vague ramblings aren't helping much, but that's kind of what I was getting at...

[imatfaal]

Shadec - At the back of my mind I am beginning to think I remember one, I believe I have heard of a parasite that whilst not great for the human host does help fight off a different parasitic infection (malaria  I think).  That would fit the bill, wouldnt it?

[williampcochran]

A bacteriophage (from 'bacteria' and Greek φᾰγεῖν phagein "to eat") is any one of a number of viruses that infect bacteria. Bacteriophages are among the most common biological entities on Earth.[1] The term is commonly used in its shortened form, phage.

Typically, bacteriophages consist of an outer protein capsid enclosing genetic material. The genetic material can be ssRNA, dsRNA, ssDNA, or dsDNA ('ss-' or 'ds-' prefix denotes single-strand or double-strand) along with either circular or linear arrangement. Bacteriophages are much smaller than the bacteria they destroy.

Phages are estimated to be the most widely distributed and diverse entities in the biosphere.[2] Phages are ubiquitous and can be found in all reservoirs populated by bacterial hosts, such as soil or the intestines of animals. One of the densest natural sources for phages and other viruses is sea water, where up to 9×108 virions per milliliter have been found in microbial mats at the surface,[3] and up to 70% of marine bacteria may be infected by phages.[4] They have been used for over 60 years as an alternative to antibiotics in the former Soviet Union and Eastern Europe.[5] They are seen as a possible therapy against multi drug resistant strains of many bacteria.

[CliffordK]

Leaches... aren't something just out of the Rambo Films...

But they are used in Western Hospitals right here in the USA as part of therapy.

When reattaching severed fingers...  it is relatively easy to reconnect the severed arteries, but far more difficult to reattach the severed veins.  So they reconnect up all the arteries and ignore the veins. 

The leaches are able to suck up enough deoxygenated blood that the finger survives until the veins naturally regrow.

I suppose that isn't necessarily saving the whole person, but a finger can be pretty important.  And, it is aiding in the survival of the digit.