Food bug Listeria can cause heart problems

London: Some variants of the common food bug, called Listeria monocytogenes, appear to have an enhanced ability to increase the risk of serious heart diseases, a new study has claimed.

Researchers at the University of Illinois, Chicago, found that some deadly strains of the bug are "uniquely adapted" to invade heart tissues of people with pre-existing heart problems, or who have had heart valve replacements.

In a study on mice, the scientists discovered that the animals infected with the strains had up to 15 times more bacteria in their hearts than those exposed to other forms of Listeria.

The findings, the researchers said, could help develop new ways of identifying the strains and protect those most at risk, the Daily Mail reported.

Listeria monocytogenes is widespread in the environment, living in soil and vegetation, and exists harmlessly in the the guts of at least five per cent of healthy people.

According to the researchers, the bacteria has an unusual ability to grow in low temperatures and can be found in a wide range of foods including soft cheeses, cold meat products, raw vegetables, fish, salads and unpasteurised milk.

Listeria infections may cause nothing worse than flu-like symptoms and a upset stomach or lead to serious illness involving the blood and nervous system. Pregnant women are especially susceptible to Listeria, which can cause them to miscarry, the researchers said.

Researcher Nancy Freitag, a professor at the University of Illinois, explained how a subset of infections followed a different path.

She said,"A significant number – about 10 per cent -of L. Monocytogenes infections involve the heart. In these cases, death rate from cardiac illness is estimated to be up to 35 per cent, yet very little is known about how these bacteria infect heart tissues."

Dr Freitag`s research showed that some Listeria strains had modified surface proteins which helped them home in on the heart. The scientists are now working on developing diagnostic tests based on bacterial genetic markers.

"These tests could be used to distinguish strains of Listeria isolated from food outbreaks, food processing plants, or from clinical infections that place patients at increased risk of cardiac disease," said Dr Freitag.

"This would allow health care workers and food safety officials to closely monitor exposed individuals."

She added, "Patients with heart valve replacements or prior cardiac illness are believed to be more susceptible to Listeria cardiac infections. It is not clear exactly why this is so, but it could be that damaged tissue provides an additional entry way for infection."

The new research is published in the Journal of Medical Microbiology.