In a report in this issue of Science,
Shirakawaet al.
(
p. 77) show an inverse
relation between exposure to the bacterium that causes tuberculosis and the
incidence of asthma, leading to the proposition that childhood infections can
protect against later development of asthma and similar allergic reactions. In
their Perspective, Cookson
and Moffatt
explain the immunological basis of this proposition and discuss its
implications.
Crohn's
disease, a serious disorder of the intestines, appears to be increasing sharply
among children, a trend that may refelct some unknown influence of Western
industrial civilization, a British scientist said yesterday at a scientific
symposium in Houston.
"It's
almost as if the infection-free environment of modern Western society could be a
factor," said Dr. John Walker-Smith of St. Bartholomew's Hospital in London, an
expert on intestinal diseases of children...
....Dr.
Walker-Smith said it was possible that the decline of many childhood infections
might allow children in the West to grow up without the vigorous development of
their immune defense systems that such infections would ordinarily promote.
In the last year, the world of
infectious diseases has begun to lose its bearings. The simple John Wayne-like
world where the good guys (vaccines, antibiotics and hand washing) chase away
the bad guys (bacteria, viruses and all the rest) is fading fast into the
sunset.
Rather, some investigators are
arguing that, contrary to your mother's (and everyone else's) advice, many of us
are not receiving enough infections. Writing recently in The New England
Journal of Medicine, Dr. Scott Weiss of the Channing Laboratory at Harvard,
referred to the new focus as the "eat dirt" approach to health.
The idea, although perhaps
unsettling, is neither new nor that complicated. As miserable as infections make
us feel in the here and now, routine constant low-grade colds, flus
and stomach viruses represent useful assaults on our immune systems. As such,
they resemble the relentlessly upbeat personal trainer who preaches the doctrine
of no pain, no gain. Infections keep us, and our immune systems, fit and ready
to go.
A result is an immune system of great
sophistication, forever primed to tackle the various assaults that lie ahead.
The final consequence of all of this, according to the theory, is that — maybe —
those who grow up in less hygienic, less germ-free and less vaccine-punctured
environments have substantially lower rates of an array of autoimmune and
allergic diseases like multiple sclerosis, Crohn's
disease, asthma and eczema.
The story is a classic medical tale of epidemiologic observation, leading
first to head scratching, then to a flurry of guesses and high-end theories and,
finally, to basic scientific evidence to buttress the initial observation.
...It
is, of course, well known that preventing or treating an infectious disease can
have profound effects on the pathogenic organism that causes it. The evolution
of drug-resistant strains is the most famous example of such an effect. Others,
equally disturbing, include the appearance of mutants able to evade the
protection conferred by vaccines. But now a new worry has emerged. It appears
that intervening in infections may have undesirable effects on the hosts—that
is, on people—as well as on the pathogens themselves.
....childhood infections do indeed seem to reduce the probability of chronic
disease—an idea known as the “hygiene hypothesis”.
...The
second possible effect of intervening in a disease is that the intervention
makes the disease worse in the long term, not better. A number of viral
infections—chickenpox and polio, for example—are more dangerous to an adult than
an infant. If a disease is dangerous and no effective vaccine or treatment for
it exists, it might be better to allow a child to catch it early on rather than
to try to delay or prevent the disease.
Infants who go to day-care centers or
who have older siblings are less likely than those who don't to develop asthma
later in childhood, perhaps because they are exposed to more germs, researchers
say.
The new findings provide strong support
for the provocative but increasingly accepted theory that exposure to microbes
early in life may help the immune system mature properly, lowering the risk of
asthma and allergies.
Early infection and subsequent insulin dependent diabetes.
Gibbon C, Smith T, Egger P, Betts P, Phillips D.
MRC Environmental Epidemiology Unit, University of Southampton.
In a study of 58 children under the
age of 16 with insulin dependent diabetes (IDDM)
and 172 matched non-diabetic controls, infection during the first year of life
was associated with a reduction in diabetes risk (odds ratio 0.81, 95%
confidence interval 0.67 to 0.98, per infective episode). Decreased exposure
to common infections during infancy may be linked with subsequent IDDM.
DISCLAIMER: All
information, data, and material contained, presented, or provided here is for
general information purposes only and is not to be construed as reflecting the
knowledge or opinions of the publisher, and is not to be construed or intended
as providing medical or legal advice. The decision whether or not to vaccinate
is an important and complex issue and should be made by you, and you alone, in
consultation with your health care provider.
