As much as you’d probably like to forget the perils of having a chronic infection like H. pylori or herpes, you may not expect that some common viruses and bacteria may actually cause long-term memory and cognition problems. A new study published in today’s issue of the journal Neurology suggests just that.

The authors assessed the infectious burden of five common viruses and bacteria in 1,625 older New Yorkers. They found that those who have showed stronger signs of infection with one or more of these agents performed worse on a commonly-used memory test.

Infectious burden can be defined as the number of infections a person can have at any time. Our infectious burden grows as we get older and are more exposed to more infectious agents. As one is infected with a virus or a bacteria, the body’s immune system creates antibodies in response to a specific pathogen. Hence, the level of these antibodies can indicate either a current or previous infection. With the collected frozen blood samples, they measured infectious burden by analyzing levels of antibodies.

They studied three viruses and two bacteria: herpes simplex virus types 1 (oral) and 2 (genital), cytomegalovirus, chlamydia pneumoniae (a common respiratory infection), and Helicobacter pylori (a bacteria that has been known to cause stomach ulcers). Past research has associated these pathogens with vascular disease, including atherosclerosis and strokes.

Those with a higher infectious burden were up to 25% more likely to get low scores on the Mini-Mental State Examination (MMSE), which is used to assess for cognitive deficits related to Alzheimer’s and other forms of dementia. The effects were more pronounced among women, those with lower socioeconomic status, and the physically inactive. Those who were physically active, however, didn’t have the cognitive deficits associated with a higher infectious burden – suggesting a protective benefit of exercise.

More studies are needed to assess the exact link between these infectious agents and memory problems. However, it adds weight to the growing theory that Alzheimer’s disease and other forms of chronic memory loss are linked to the “inflammatory milieu” from these infections, which can cause vascular damage in the brain.

The authors also think this may help find new ways to prevent cognitive problems in the future. “The results could lead to ways to identify people at risk of cognitive impairment and eventually lower that risk,” said Mira Katan, the primary investigator of the study. “For example, exercise and childhood vaccinations against viruses could decrease the risk for memory problems later in life