This title may seem odd, but this item may actually turn out to have enormous implications for all of us.
A couple of years ago I read a fascinating book: Parasites and the Behavior of Animals, in which the author – Janice Moore from Colorado State University – cataloged some of the extraordinary ways in which parasites can impact the behaviors of a vast array of animals. As difficult as it is to interpret studies of parasites in humans, I kept coming back to some odd observations about an illness with which I’ve been involved for more than 30 years: schizophrenia. I kept wondering if some of the odd observations made over the years could be explained by the parasites?
What kind of odd observations?
- Reports of mental illness have been found throughout history, yet this strange illness that we now call schizophrenia seems to have been very rare until about 1750, when it increased dramatically throughout Western Europe. I have had the privilege of working at the Bethlem Royal Hospital from which got the word “bedlam.” I know of the incredible records kept there. Something began to change in some of the types of patients being admitted at that time. I have also had the opportunity to look at some of the records at the Philip’s Hospital in Southern Germany, which has been in existence since 1533. Again the records show the sudden appearance of many cases of something that had been quite rare until then. 1750 marked the early years of the industrial revolution in Europe and the mass migration of people from the countryside to the new and very crowded cities
- There has been recent evidence that being born and raised in a city increases your chance of developing schizophrenia.
- There is increasing evidence that acute episodes of psychosis, mania and depression are associated with increases in circulating inflammatory mediators. There is also intriguing new data that both psychosis and depression can be improved by giving people COX2 inhibitors.
- There has also been the strange observation that bipolar disorder may have been becoming more common in recent years, over and above our greater ability to recognize the illness.
Several years ago the well-known psychiatrist E. Fuller Torrey first suggested that a small protozoal parasite called Toxoplasma gondii might be responsible for all of these observations. Cats can carry it, which is why pregnant mothers are advised not to pet their cats during pregnancy.
The idea that such a complex disease as schizophrenia might sometimes be caused by a parasite caught the media’s attention, but in recent years the story – but not the ongoing research – died down a bit.
There was an excellent and provocative blog item by Carl Zimmer about this almost three weeks ago, but I wanted to check everything out before responding. He gave a brief review of a new paper published in the Proceedings of the Royal Society, by Kevin Lafferty from the University of California in Santa Barbara. Lafferty has attempted to correlate the varying rates of Toxoplasma in different countries with predominant personality traits and therefore – since our societies are aggregates of all our personalities, cultural characteristics.
That may all sound far-fetched, but I don’t think that it is. And I don’t think that the Proceedings would have taken a completely half-baked proposition.
I have also found a report published in the journal the Proceedings of the Biological Society. Four eminent authors, including Torrey, revisited the while issue of Toxoplasmosis and mental illness. When the parasite gets into the nervous system it can alter behavior: Rats are normally programmed to avoid cats, but once infected they are attracted to cats. Over the last few days I’ve been plowing the world literature, and I’ve learned some very interesting things that support the idea that Toxoplasma may be playing a role in several different types of psychiatric illness.
There is strong evidence that schizophrenia, bipolar disorder and major depressive disorder lie on a spectrum. The illnesses are not the same, but people often switch from one type of clinical presentation to another. The precise type if illness would be determined by the interaction of genes, physical and Intrapsychic environment. Nobody would be sufficiently naïve to try and reduce the whole of psychiatric illness to a single bug. Mental illness is a great deal more than just a physical problem, and apart from anything else, the rates of Toxoplasma infections show remarkable variations around the globe, while the rates of major mental illness are much the same everywhere.
So what have I learned?
- There are a remarkable numbers of studies showing that many people with schizophrenia have antibodies to Toxoplasma, including people having their first attack of the illness
- Blood donors infected with Toxoplasma have decreased levels of novelty-seeking
- In women who become infected, there are some marked changes in personality.
- Toxoplasma affects the dopamine systems of the brain that we know are intimately involved in mood, cognition, movement and motivation.
- Some drugs used to treat psychosis (haloperidol) and mood disorder (valproic acid) inhibit the replication of Toxoplasma gondii. The valproic acid already does it at concentrations lower than we normally aim for when treating humans.
- There is some intriguing work going on into the use of antibiotics to kill Toxoplasma and reverse its behavioral effects.
In the last few years, so many illnesses have turned out to have infectious origins, from peptic ulcers to arteriosclerosis and some cancers. Perhaps some mental illnesses will be next.
Last year Barry Marshall and Robin Warren were awarded the Nobel Prize in Physiology or Medicine for their pioneering work on Helicobacter. I have a strong sense that there are more prizes to come on the interaction between infectious agents, inflammation, genes, the psyche and the environment.
Perhaps the reason that some antipsychotics and mood stablizers can reverse some of the neurological damage associated with schizophrenia and bipolar disorder is becuase they are killing off the causative agents and allowing the brain to repair itself.
I shall keep you posted!