| JWissmille 2004-08-26, 10:08 pm |
| "And other established links, such as that between Lyme disease and
neurologic symptoms, also could go unrecognized, Dr. O'Connor said."
http://www.ama-assn.org/amednews/20...19/hll20719.htm
HEALTH & SCIENCE
Infection eyed as culprit in chronic disease
There are skeptics, but this line of research is gaining attention.
By Susan J. Landers, AMNews staff. July 19, 2004.
------------------------------------------------------------------------
Washington -- Imagine prescribing antibiotics for patients with
atherosclerosis, or administering vaccines to prevent schizophrenia.
Many researchers are thinking outside the box and are pursuing the
infectious agents they believe might play a large role in causing
chronic diseases.
"It is becoming increasingly acceptable and recognized that infections
are probably an underappreciated cause of chronic disease," said Siobhan
O'Connor, MD, MPH, assistant to the director of the National Center for
Infectious Diseases at the Centers for Disease Control and Prevention.
The list of chronic diseases known to be caused by infectious agents is
growing. AIDS, cervical cancer, liver cancer and peptic ulcers all
result from these bugs, and researchers are exploring links to heart
disease, additional cancers and psychiatric disorders. About 70% of all
deaths in the United States are caused by chronic diseases, making them
a prime target for research attention.
There was a time when the very idea of an infectious agent causing a
chronic disease brought heaps of scorn upon the scientists who proposed
it. That's what happened in the 1980s when it was suggested that ulcers
were caused by /Helicobacter pylori/ rather than stress and spicy food.
Since then, /H. pylori/ has been linked to duodenal ulcers, gastric
cancer and certain types of lymphomas.
The ulcer story caused a shift in thinking that went well beyond that
one disease, said E. Fuller Torrey, MD, associate director of laboratory
research at the Stanley Medical Research Institute. He has been
examining the role of infectious agents in schizophrenia and bipolar
disorder "for more years than I care to remember." As for the current
status of his research: "I wouldn't say we were respectable, but we are
no longer not respectable, either."
His work with Robert H. Yolken, MD, professor of pediatrics at Johns
Hopkins university in Baltimore, has recently centered on the roles of
the herpes viruses and a parasite, /Toxoplasma gondii/, as possible
triggers for the psychiatric disorders.
But in general, even if an infection plays some role in chronic disease,
it is hardly the sole cause, experts agree. Drs. Torrey and Yolken
devised a working hypothesis, for instance, stating that most cases of
schizophrenia are generated by infections and other environmental events
occurring in genetically susceptible individuals.
The role of genes in many disorders has been recognized for about a
century, Dr. Torrey noted, and the hope was that sequencing of the human
genome would solve the riddle of chronic diseases and present a cure.
"If you asked someone in the mid to late 1980s where we were going
researchwise, they would say these are genetic diseases, and as soon as
we get the human genome sorted out, we will identify the genes involved
and we can all go home and play golf," Dr. Torrey said. "That clearly
has not been the case." What is clear to him is that multiple genes are
involved in many diseases, and evidence points to a link between
predisposing genes and infectious agents. "That made our research of
greater interest."
The role of infection in cardiovascular disease is another area that,
while not yet accepted, is attracting notice, particularly since heart
disease is the No. 1 killer in the United States.
For example, recent studies have linked several common infections with a
person's risk of developing atherosclerosis. It is possible that a bug
causes the disease, said Michael Dunne, MD, vice president of clinical
development in infectious disease at Pfizer Inc. /Chlamydia pneumoniae/
is his prime suspect at the moment. "If you look at the arteries at
autopsy of people with atherosclerosis you find evidence of /Chlamydia/
in 50% or 60% of patients."
"The next step is: Can you do anything about it?" Dr. Dunne asked.
That's where a series of antibiotic trials enter the picture. Although
early results have not been positive, the findings from large trials
scheduled for release later this summer could show whether a course of
antibiotics is beneficial to heart patients.
Continuing search for MS trigger
The search for an infectious trigger for multiple sclerosis also has
been under way for decades, said Richard T. Johnson, MD, distinguished
professor of neurology, microbiology and neuroscience at Johns Hopkins
School of Medicine.
When he first began researching the causes of MS in the 1960s, there was
a firm conviction that the disease was due to an external agent, most
likely a virus. But the early suspects turned out to result from
mistakes, either misidentifications or lab contamination. That caused
the idea to fall out of fashion.
Recently, however, interest peaked again. The targets are four rather
ubiquitous agents: /Chlamydia pneumoniae,/ herpes virus 6, Epstein-Barr
virus and endogenous retroviruses. Since all are common, research is
focusing on the quantity of the microbes and their location in the body.
"That's a very interesting but complicated argument," Dr. Johnson said.
New technologies should help with the recognition of novel agents or
already established agents in chronic disease, Dr. O'Connor said. "We
also need to design epidemiologic studies in a more rigorous fashion so
they are reproducible," she added.
Meanwhile, some of the confirmed relationships between infections and
chronic diseases aren't receiving sufficient consideration in the
clinical world, she said. Even the well-established link between /H.
pylori/ and peptic ulcers may be missed.
And other established links, such as that between Lyme disease and
neurologic symptoms, also could go unrecognized, Dr. O'Connor said.
There are also prevention opportunities to be seized, she said. For
example, physicians can tell patients that they have the power to
prevent some liver cancers by avoiding exposure to the hepatitis B and C
viruses.
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