Viruses, but not bacteria, tied to mental decline

Past infection by multiple common viruses may contribute to dementia in some elderly people. Viruses can trigger inflammation in tissues they infect, and inflammation of brain tissue had previously been linked to mental decline.

To explore this connection, Timo Strandberg and his colleagues at the University of Helsinki tested for antibodies to three viruses and two bacteria in 383 volunteers over age 75 who had cardiovascular disease.

The tests determined whether volunteers had been infected at some time by cytomegalovirus, a common but often symptomless agent; herpes simplex virus type 1, which causes cold sores; herpes simplex virus type 2, which is sexually transmitted; the bacterium Chlamydia pneumoniae; or the bacterium Mycoplasma pneumoniae. Both bacteria cause pneumonia.

At the beginning of the study and 1 year later, the researchers assessed whether volunteers showed evidence of mental impairment. Volunteers starting off with antibodies to all three viruses were 2.5 times as likely to be mentally impaired initially–and 2.3 times as likely to decline mentally during the study–as were volunteers with antibodies to none or just one of the viruses.

Infection by two viruses had intermediate effects.

The researchers found no significant relationship between the bacterial infections and mental impairment either at the beginning or end of the study, they report in an upcoming Stroke.

Past studies have hinted that herpes simplex viruses and cytomegalovirus, all of which are active in brain tissues, might be associated with dementia. Other viruses may contribute to another mental disorder, schizophrenia (SN: 4/14/01, p. 228: Available to subscribers at Viruses may play a part in schizophrenia).


If you have a comment on this article that you would like considered for publication in Science News, send it to Please include your name and location.

More Stories from Science News on Health & Medicine