Studies Find More Heart Disease, Infection Links

November 7, 2000

WASHINGTON (Reuters) -- Three studies to be published on Tuesday strengthen theories that infections may be linked with heart disease in some cases.

People infected with herpes simplex, the virus that causes cold sores, were twice as likely to have a heart attack or die from heart disease as uninfected people, one study found.

A second study found that bacteria linked with heart disease ride into the circulatory system in immune-system cells. A third found that patients with symptoms of infection had poorer blood flow and were more likely to suffer the blood clots that cause heart attacks and strokes.

"Infections are of interest, in part, because of the increasing attention paid to the role of inflammation in heart disease," Dr. David Siscovick, a professor of medicine and epidemiology at the University of Washington in Seattle who led the first study, said in a statement.

Writing in the journal Circulation, published by the American Heart Association, Siscovick and colleagues said they looked at blood samples from 600 people with an average age of 74, 200 of whom had suffered heart attacks, to see if infection was associated with heart attack.

They looked for antibodies, which are immune-system molecules generated by infection, against herpes simplex; against Chlamydia pneumonia, which causes respiratory tract infections and which other studies have linked to heart disease; and against cytomegalovirus (CMV), a herpes virus that is common but usually produces no symptoms.

"Eighty percent had antibodies to all three," Siscovick said in a telephone interview. "All three infections are common."

Antibodies to herpes simplex were associated with a doubled risk of heart attack and death from heart disease. There seemed to be no link to CMV and heart disease.

Other studies have found a link between all three infections and atherosclerosis.

Atherosclerosis, or coronary artery disease, is caused when immune-system cells latch on to cholesterol particles and try to pull them out through the blood vessel walls. They get stuck because they are too big and the result is a "plaque" or clogged area.

Scientists think inflammation, perhaps caused by a bacterial or viral infection, might bring in more immune cells and worsen the process of atherosclerosis. Several studies have found Chlamydia bacteria in these plaques.

Siscovick found no direct evidence that people with Chlamydia antibodies were more likely to develop heart disease. "However, in patients with very high levels of the antibodies, there was evidence of a possible association," he said.

He warned that no one should draw any conclusions -- yet.

"I think the message is not for everybody to feel if they had a cold sore ... that they are going to have a heart attack," he said.

"About 35 percent of people end up dying from coronary artery disease -- it is a common condition. This does not mean that traditional risk factors (such as diet and exercise) aren't important."

In a second study, a team at the University of California, Davis, examined immune-system cells from 28 heart patients and 19 healthy blood donors, looking for DNA from Chlamydia.

They found the DNA in the cells of 13 of the heart disease patients and five of the healthy donors. In 15 of these 18 people, the DNA was inside white blood cells called CD3 T-cells -- which are known to build up in artery deposits.

"Because we found Chlamydia pneumonia DNA in T-cells, it suggests this is how the infection reaches the heart vessels," Ravi Kaul, who led the study, said.

In the third study, University of California San Francisco researchers checked the records of 975 people being treated with clot-busting drugs for heart attacks, measuring their white blood cell count.

"Patients with inflammation -- elevation of their white blood cell count -- had poorer blood flow into the heart muscle and more blood clots in the artery receiving the clot-dissolving drug than patients with low white cell counts," Dr. Michael Gibson, who worked on the study, said.

His team found the higher the white blood cell count, the higher the patient's risk of dying from a heart attack or developing congestive heart failure.