Question

[Bart_Corsaro_at_USLRMG01 at INTERNETMAIL.PR.CYANAMID.COM]

Ursula asked if there are any benificial viruses.  Several people replied that
the paramyxoviruses introduced into the Austrialian rabbit population were 
benificial to humans but, rightly so, not to the rabbits.  While this may be
true, it does not address the issue of commensal or symbiotic viruses. 

I can think of one group of symbiotic viruses, the Polydnaviruses.  These
viruses are carried by every Braconid and Ichneumonid paristoid wasp and do not
appear to have any detrimental effect on the wasps.  The parasitoids inject
their eggs into insect larvae (host).  The viruses coat the eggs
of the parasitoid and protect the egg from the insect host's immune system. 
This has been proven in a number of experiments in which parasitoid egg stripped
of the virion are destroyed by the host's immune system.  Other effects on the
parasitized host that have been attributed to the virus include growth
inhibition, hormonal perturbation and a reduction in phenol oxidase activity.

This relationship brings up a new twist to an old question - which came first
the virus or the egg.

Bart Corsaro
Wyeth-Lederle Vaccines and Pediatrics
Email: Bart_Corsaro_at_USLRMG01 at internetmail.pr.cyanamid.com




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