All sorts of things can make us sad, anxious or depressed: a bad day at work, money problems, a family row. But could you be feeling some of those same emotions simply because you have been infected by a bug?
Studies suggest bacteria and parasites may change personality. Some experts even now believe we can “catch” depression, and, if we”re lucky, happiness.
We’ve all experienced the physical effects of a bacterial infection like a tummy bug. Our immune system fires up chemical messengers that produce inflammation to fight the infection, which, in turn, makes us crawl to our beds. So how could an infection also alter our mood?
One theory is that bacteria affect the balance of our brain chemicals, triggering changes in behaviour. Here, we look at the effects certain bugs can have on our personality.
The bug that makes you frisky
Toxoplasma gondii, a parasite found in cat faeces, is harmless to most of us. But studies suggest it can change behaviour in a small set of susceptible people.
Dr Nicky Boulter, an infectious disease researcher at Sydney University of Technology, says men and women respond differently to T.gondii infection: “Infected men have a lower IQ, shorter attention span and are more likely to break rules and take risks. Women are more outgoing, friendly and promiscuous.”
The parasite has also been linked with more serious psychiatric disorders such as schizophrenia, bi-polar and obsessive compulsive disorder. It seems to increase levels of two brain chemicals, dopamine and glutamate, which are associated with mood and social interaction.
“If T.gondii is shown to be a cause of mental disorders, it will constitute a major breakthrough in understanding how psychiatric problems start and the mechanisms that control them,” says Abebaw Fekadu, lecturer in the neurobiology of mood disorders at the Institute of Psychiatry in London.
The bug that makes you clever
Researchers investigating the ability of bacteria called Mycobacterium vaccae to destroy prostate cancer noticed that it also made patients more cheerful.
It turned out the bacteria was stimulating an area in their brains involved in producing the feel-good chemical serotonin.
“It’s odd because infection usually produces inflammation and makes people feel worse,” says Graham Rook, professor of medical microbiology at the Royal Free and University College Medical School inLondon.
“We think M.vaccae is somehow able to damp down inflammation, allowing the serotonin to have itseffect.”
The hope is that this could lead to a new form of antidepressant.
“M.vaccaae is found in soil and is easy to inhale or get on your hands,” says Dorothy Matthews, associate professor of biology at Sage Colleges in Troy New York.
She’s found that it seems to improve learning, too. Mice fed on M.vaccae went through a maze twice as fast as those who hadn’t had any.
So could this work for humans?
“I’d certainly recommend children get out in the country more,” says Professor Matthews. “Exposure to this bacteria could cheer them up, and it might improve their learning.”
But Professor Rook doubts even gardeners would be able to get enough of it to have a beneficial effect.
The bug that makes you sad
“If you have a serious infection - say, a bad bout of food poisoning - you just want to go to bed, sleep and not do anything,” says Dr Naomi Eisenberger, a psychologist at the University of California.
“It’s known as the inflammation response, and it’s the body’s way of making sure that you devote all your energies to fighting off the infection. What’s interesting is that this behaviour is similar to what we see in some people with depression.”
Dr Eisenberger gave 39 people a small dose of bacterial toxin taken from the E.coli bug and then got them to fill in a questionnaire. The answers showed two changes in mood: they had became less interested in the promise of financial rewards and in interacting with other people.
Checking the levels of inflammation against brain scans revealed that areas where activity had changed are known to control willingness to take risks.
New bacterial and other treatments could emerge from all this research. In the meantime, there may be a more immediate way of improving our psychological state using the complex web of bacteria living in our guts.
“Evidence suggests gut bacteria can communicate directly with the brain,” says Professor Glen Gibson, a microbiologist at Reading University. “It’s early days, but studies have found that giving tiny amounts of probiotics (friendly gut bacteria) canÊaffect parts of the brain involved in emotions.”
So could we soon be taking probiotics instead of antidepressants? Maybe, says neuroscientist Professor John Cryan.
“You won’t be able to use something off the supermarket shelves,” he adds, “but there is a small study on humans showing that a particular strain of friendly gut bacteria can reduce depression.” - Daily Mail