may be hard to imagine a world devastated or thrown into panic by the
flu. But several times during the 20th century, unusually
deadly influenza strains caused epidemics that killed hundreds of thousands
of people. In 1918
for example, while our country mobilized for World War I, an influenza
epidemic swept across the country, killing 675,000 Americans and somewhere
between 20 and 50 million people worldwide more
than all the wars of the 20th century put together . This epidemic
is seldom mentioned, and most Americans seem to have forgotten about
it altogether. To get an idea of how serious it actually was, read this
from a doctor stationed at Fort Devens in Massachusetts.
influenza would be a lot simpler if the virus that caused it could only
infect our species. But in fact, influenza viruses also infect other
animals. Does that surprise you? Most of us, if we think about this
subject at all, usually think of "our" diseases as separate
from illnesses of other species. Sure, the threat of bioterrorism reminded
those of us who don't live in cattle country that both livestock and
humans can get anthrax.
And we've learned that ticks jumping from deer to mice to humans can
sometimes carry Lyme
disease. But most of the time, we act as though those cases
aren't. Many infectious diseases affect a wide range of host species.
You may or may not know that after researchers discovered the Human
Immunodeficiency Virus (HIV), they discovered very similar Simian Immunodeficiency
Viruses (SIV's) that infect chimpanzees and other primates. Then they
Immunodeficiency Viruses (FIV's)
in domestic and wild cats (including lions and cheetahs), and several
other groups of viruses in other groups of mammals. (See M&L
web feature (to come) "What do AIDS, Flu, SARS, Lyme Disease, and
West Nile Virus have in common?")
true for influenza
too. Different strains of influenza
viruses attack many other species, including ducks, chickens, turkeys,
pigs, horses, and ferrets. Some virus strains can jump from one host
species to another especially if the host species are closely
related. Several strains, for example, readily infect humans, pigs,
and ferrets. Remember this point, because it is a vital clue to the
way serious flu epidemics can arise.
Japan have also been hard hit by the Avian flu this year
influenza strains, however, are usually restricted to one group of closely-related
host species. Avian
(bird) flu strains, for example, can often infect several species
of birds but seldom, if ever, cause disease in humans. And here's the rub: because avian
strains do not normally infect our species, they evolve separately from
human strains. As a result, bird viruses often carry different genes
that code for proteins on the outer virus coat that differ significantly
from the coat proteins of human virus strains. This, as you will see
shortly, is what makes these strains potentially dangerous to us.
of this Web Article:
Introduction What's up with the Flu?
What is influenza and who gets it?
can we get the flu again and again? And why can't we develop a one-time
How are flu vaccines made?
Why are flu vaccines sometimes not effective?
Why are researchers so worried about this
new bird flu?