aggressive viruses

[Denni Schnapp]

What about viruses which can survive in alternative host or just hang about
in the environment until the host they usually attack comes along again?
Certain insect viruses seem to be able to completely kill their host in some
patches which are subsequently re-colonised by hosts ehich have managed to propagate in virus-free patches. And Ebola Zaire is thought to have alternative
hosts which may act as carriers without being too badly affected. Finally,
immunity within a population may vary a lot so after a parasite attack very
few hosts may survive but they are immune against future atack (10% survive
Ebola Zaire infection)but eventually either the parasite evolves to catch
up with these immune hosts (in the meantime some of the population will
also have acquired immunity against this altered parasite...) or variation
will have returned to the population due to inter-breeding. Something like this
seems to be the case with guppies, males can only develop their mating
colours if they are free of certain parasites thus advertising their immune
status to mature females. However, the parasite keeps catching up and it
seems the genetic traits the immune males display change from year to year...

Gretings,

Denni