As I understand it, viruses that affect one species (like a duck) rarely cause 
illness in another species, because the virus is adapted to lock onto the cells of a givebn host. Now, we see that several new viruses have appeared (in SE China, Asia), which are capable of infecting human beings. How does a virus changes such that infection of another species becomes possible?
I know that SE China is an excellent breeding ground for avian viruses…you have large numbers of humans, pigs, and birds (ducks,chickens, geese) living together in close proximity…so transmission between the species is easy.
Is this a warning to us? Are there simply so many inhabitants (human and animal) that this typeofspecies-crossing virus is going to become more common? Or is thephenomenon something that has always been going on?
Incidentally, last week there was news of a biologist in Texas, who was able to revive ancient bacteria spores found in a 250million year old salt crystal…could ancient viruses cause a human epidemic?
From what I understand, one of the concerns with Avian flus is that if someone who is currently suffering from a human-borne influenza manages to get infected by an avian strand, the information between the two strains of flu can be shared. This then leads to an “upgraded” strain of avian flu that is easily spread among humans. While the strain wasn’t deadly to birds, who have had a long time to develop their immune system to respond to a particular strain of flu, the human immune system is not able to handle it.
I would highly recommend checking out the center for disease control or WHO websites for some real information instead of reading newspaper headlines. I remember all this same BS floating around last year over SARS, and about 99% of those headlines was proven to be pure crapola.
http://www.cdc.gov/flu/avian/
http://www.who.int/csr/disease/avian_influenza/en/
Is there anything in the posts in this thread that are “BS”?
The viruses that jump species most often are influenza viruses, which are unusual in that they have eight strands of RNA that function sort of like chromosomes. So normally, avian flu viruses have a hard time infecting humans. But when a human is infected with an avian flu virus and a human flu virus simultaneously, they can mix up their genes, resulting in a new avian-like flu that can easily infect humans.
ralph124c: “As I understand it, viruses that affect one species (like a duck) rarely cause illness in another species”
As far I can tell, that’s true. The catch is that when so many humans spend so much of their time around so many animals, sooner or later they’ll come into contact with a virus or bacteria capable of surviving in both species.
" Is this a warning to us? Are there simply so many inhabitants (human and animal) that this typeofspecies-crossing virus is going to become more common? Or is thephenomenon something that has always been going on?"
According to Jared Diamond’s Guns, Germs and Steel, this has been going on almost since humans first started domesticaing animals. It was the continued exposure (and the partial resistances that eventually built up) to initially animal-borne diseases (measles, mumps, flu, etc) that led to the European explorers causing such biological havoc in the New World, whose inhabitants had not domesticated nearly as many species and so had not been exposed to as many diseases.
I reckon that’s what it is.