Common viruses may cause memory deficits

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In a study by researchers at the Mayo Clinic College of Medicine in Minnesota, mice infected with Thelier’s murine encephalomyelitis virus (which is similar to human poliovirus) had more difficulty learning to navigate through a maze than uninfected control mice.

The spatial memory of the mice used in the study was affected to varying degrees. In some of the animals, it was barely noticeable, while in others it was severe. The extent of memory impairment was seen to be directly correlated to the number of dead cells found in the hippocampus

Our findings suggest that picornavirus infections throughout the lifetime of an individual may chip away at the cognitive reserve, increasing the likelihood of detectable cognitive impairment as the individual ages. We hypothesize that mild memory and cognitive impairments of unknown etiology may, in fact, be due to accumulative loss of hippocampus function caused by repeated infection with common and widespread neurovirulent picornaviruses. Further analysis of such deficits and exploration of potential therapeutic interventions is clearly needed.    

Picornaviruses include rhinoviruses (pictured), which cause the common cold,  and enteroviruses, which cause infections of the respiratory system and gastrointestinal tract. They are the most common infectious agents in humans – globally, 1 billion people are infected with some type of picornavirus every year, and an individual will, on average, be infected 3 or 4 times a year.  The authors say that because picornavirus infections are so widespread, they may pose a real medical problem, and that their findings warrant further investigation.

Many different types of viruses are known to infect the nervous system. For example, polio, herpes and some types of meningitis are all caused by viral infections. It has even been suggested that rhinovirus and herpes virus infections in pregnant women may disrupt neural development in the fetus, leading to schizophrenia later on in life. But this is perhaps the first time that viral infection has been implicated in having an effect on cognitive functions. 

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