[Paleopsych] NYT: More Diseases Pinned on Old Culprit: Germs
checker at panix.com
Tue May 17 16:50:50 UTC 2005
More Diseases Pinned on Old Culprit: Germs
By NICHOLAS BAKALAR
Infectious disease used to be a simple matter: this germ causes that
illness. Doctors just had to find the germ, kill it, and cure the
But the old rules no longer apply.
A report issued last month by the American Academy of Microbiology
paints a much more complex picture of infectious disease. Germs,
scientists are learning, are probably the cause of many illnesses that
were never thought to be infectious, and determining exactly how a
germ contributes to disease is no longer simple.
The old rules date to 1883, when the German bacteriologist Robert Koch
laid down three laws - now called Koch's postulates - that infectious
disease specialists have used ever since to determine whether an
organism causes a disease: The suspected germ must be consistently
associated with the disease; it must be isolated from the sick person
and cultured in the laboratory; and experimental inoculation with the
organism must cause the symptoms of the disease to appear.
In 1905, a fourth rule was added: The organism must be isolated again
from the experimental infection.
Using Koch's postulates as a starting point, scientists figured out
the cause, prevention and treatment for one infectious disease after
another. In the mid-20th century, some experts began to believe that
infectious disease might be permanently conquered. But microbes have
been found to metamorphose into new and more destructive forms, to
jump from animals to humans, to hide where they are hard to find and
to resist the most powerful antibiotics available.
Moreover, said Dr. Ronald Luftig, an author of the academy's report
and a professor of microbiology at the Louisiana State University
Health Science Center, "There have been a lot of chronic human
illnesses thought to be genetic or environmental, but when you look at
them in more detail, it turns out there's involvement of bacteria,
groups of bacteria or viruses."
Microbes use a variety of mechanisms to attack cells and create havoc.
Human papillomavirus, for example, inserts its nucleic acid into host
cells, integrating into the cell's genes and altering the normal
process of cell division to cause the uncontrolled growth of cervical
Hepatitis B invades the liver, provoking an immune response that
stimulates the scarring, cirrhosis and fibrosis that can lead to liver
failure. At the same time, it causes genetic mutations that promote
tumor growth and deadly liver cancer. Crohn's disease, a chronic
inflammation of the intestines, may result from the presence of an
infectious organism combined with a person's genetic susceptibility.
By suppressing the immune system, inhibiting cell division and
directly affecting the function of cells, germs demonstrate an
astounding subtlety and resourcefulness in creating biological chaos.
And it gets worse. Some microbes can contribute to more than one
disease. The papillomavirus, for example, can lead not only to
cervical cancer, but also to cancer of the penis and anus, venereal
warts, common warts and cancers of the head and neck. Epstein-Barr
virus, the cause of infectious mononucleosis, is almost as versatile,
associated with Burkitt's lymphoma in Africa and with throat cancer
and Hodgkin's disease, among other cancers.
Helicobacter pylori, found in the mid-1980's to be a cause of peptic
ulcer disease, was later implicated as a contributor to gastric
lymphoma as well.
Even saying that a microbe "causes" a cancerous lesion is problematic.
Dr. David S. Pisetsky, a professor of medicine at Duke University
Medical Center, points out that most infections do not lead to cancer,
and he hesitates to alarm patients by overstating the connection.
"These viruses are associated with cancer, but causality is
complicated," he said. "In many instances, the viral infection is part
of a chain of causality, and not the sole factor."
The important questions to ask, Dr. Pisetsky adds, are "What's the
risk, and how can I reduce the risk?"
"If you have a virus associated with neck and head cancer," he said,
"that's one more reason to quit smoking." In the case of a virus known
to lead to cervical cancer, he went on, increased vigilance is in
order, with Pap smears and regular examinations.
All of this, combined with the fact that many germs (especially
viruses) are impossible to culture in a laboratory, make it all the
harder to find the microbe that causes the illness.
Often, the first step is a simple observation of patients by
clinicians, really little more than a hunch: a doctor notices a
chronic illness that always seems to be associated with something that
This is exactly what happened when Dr. N. M. Gregg, an Australian
ophthalmologist, discovered congenital rubella syndrome. He made the
connection between the cataracts he was seeing in children and their
mothers' German measles during pregnancy.
Sometimes epidemiological patterns offer the initial hint, as was the
case with Kaposi's sarcoma, once a rare lesion caused by a type of
herpes virus that began to occur frequently in gay men whose immune
systems were compromised.
Once the association is made, the search for the organism can begin.
The gut is inhabited by hundreds of species of microbes, and the
guilty party may be hiding among them. Germs can lurk in the nervous
system, like the varicella virus that causes chickenpox and then lies
in wait to cause herpes zoster, or shingles, decades later. And some
germs can cause infection in one place in the body, and a disease in
an entirely different place. Even the most sensitive molecular
techniques are sometimes not good enough to find the guilty microbe.
There are almost certainly still unknown microbes creating chronic
illness. "One of the suspects in multiple sclerosis is Epstein-Barr
virus," Dr. Luftig said. "The DNA of the virus integrates into your
cells; it's there permanently. Is it a cause? Maybe."
Dr. Luftig suggests several other diseases that may have microbial
triggers. "There's an enterovirus that's involved in destroying
pancreatic islet cells," he said. "Maybe diabetes is caused by an
immune reaction to infection. Intrauterine exposure to infection may
play a role in schizophrenia."
No one yet knows for sure. But researchers - doctors, microbiologists,
epidemiologists, geneticists - have their suspicions, and are
"We're not saying that everything is due to microbes," Dr. Luftig
said. "But the more investigative tools we develop and the more we
have interacting groups of researchers with varying specialties, the
more we can start to pick out potential agents that were never before
More information about the paleopsych