As a result of human activities, certain pathogens, normally limited to other species, gained the ability to cross species barriers
and subsequently became established in humans.
But Ken Bell, 80, the former managing director of Ken Bell Seafood Company, said researchers should test on him rather than risk breaking the species barrier
during cell research on human-animal embryos.
"Of the few avian influenza viruses that have crossed the species barrier
to infect humans, H5N1 has caused the largest number of detected cases of severe disease and death in humans," according to the Web site for the Centers for Disease Control and Prevention.
It is one of the few avian-influenza viruses to have crossed the species barrier
to infect humans, and it is the most deadly of those that have crossed the barrier.
EFSA's Scientific Panel on Biological Hazards has said "there is no intrinsic species barrier
for sheep BSE transmission to humans", however, because of lack of data, it "cannot quantify a species barrier
From movements across the animal-human species barrier
in chapter 3, Paster moves to a discussion of the "mobility and fluidity of social relations" (232) in Jonsonian city comedy and of the humoral thinking that underlies the self-conceptions of Shakespeare's Shylock, Corporal Nym, and Malvolio.
In 1997, bird flu--an illness that normally spreads from bird to bird--jumped the species barrier
. It began spreading from birds to humans.
29 - 30 June: International conference on avian influenza in humans to be held in Paris, to discuss advances made in prevention and treatment, as well as the economic impact of the bird flu virus spreading, the risk of it mutating into the deadly H5N1 virus and crossing the species barrier
to man, prevention strategies in a non-pandemic context, prevention through vaccination.
More and more animal diseases are "jumping" the species barrier
to infect human beings, and the avian influenza strain H5N1 is no exception (see "Connecting the Dots," cover story, November/December 2004).
Only the H5, H7 and H9 versions of influenza A - the type of flu which can cause pandemics - have crossed the species barrier
While the H7 strain can be highly pathogenic among poultry and has crossed the species barrier
to humans, outbreaks in people have been less serious than those of H5N1.
While it is rare for an animal virus to cross the species barrier
and infect humans, when it does it can and understandably does, spark panic and fear around the world.