In the past few years, the longstanding theory that mental illness can be caused by infection has quietly gained speed. In her new book Infectious Madness, Harriet A. Washington reveals why.
An award-winning medical author and editor, Washington's book weaves through case studies, papers, and first-hand interviews to expose a contentious issue in the medical and science worlds, one that blurs the line between psychological and physical illness. Among the examples in her book are: the link between strep throat and obsessive-compulsive disorder, the connection between gut bacteria in the bloodstream and autism, and the contraction of the flu in utero with schizophrenia.
Whether or not mental illnesses such as schizophrenia and OCD can be caused by infection remains to be seen. But given the gravity of the illnesses, Washington hopes that scientists will continue to study the links, ultimately finding new ways to prevent illnesses we’re still struggling to treat.
The theory that mental illness may be caused by infection sounds shocking, but you say this is something we’ve known for a long time.
There’s really no question that some diseases are caused by mental illness, we’re just not in the habit of thinking of them that way. Rabies [which causes seizures, paralysis, confusion] and syphilis [which causes loss of muscle control or “paresis”] are two good examples. So we already know that some diseases are caused by infection but the big question is whether or not they are diseases that cause our society a lot of problems, like schizophrenia, bipolar disorder, or depression.
Your book uncovers some cutting-edge research that shows infection may be a factor in these cases. How big of a number are we talking?
The educated guess I got from researchers was consistent: they estimated that 10-15 percent of mental diseases are caused by infection. That number may not seem that significant at first, but if we could prevent or address that amount of mental illness without long-term medical regimens that would be a huge gain.
How strong is the actual evidence we have to prove this connection?
The evidence does not align to the traditional standards of proof. But, as one researcher told me, the traditional standards of proof are no longer good enough. We can find levels of infection that would have been invisible to earlier scientists. I think it’s really important for people to understand that we have to reevaluate the nature of proof and bring it into the modern era.
Does this mean adults are at risk of contracting a mental illness late in life?
It’s not impossible for adults to acquire a mental illness as a result of an infection, but it’s not as likely because we have immune systems that are very experienced. It’s usually very young brains—fetuses in utero, newborn babies, and young children. Their immune systems are not yet mature so when they encounter pathogens they tend to have this strong and vigorous, but not very accurate, response. Often their brains are harmed by their own immune system’s reaction. So really it’s young people who are vulnerable to this.
This theory is still very contentious in the medical world. What were the reactions like from the scientists, experts, and clinicians you spoke with?
They were mixed. There are researchers who think the theory is very sound, with various modifications, and there are others who have a lot of questions. I think PANDAS is probably the best example of this issue in the book. [PANDAS (Pediatric Autoimmune Neuropsychiatric Disorders) is a rare disease characterized by obsessive-compulsive behaviors that emerge after a bout of strep throat].
Where does the medical world stand on PANDAS at the moment?
Physicians have been lining up all over the spectrum in terms of supporting it, not supporting it, supporting some parts and not others. I think the controversial nature of the theory is very illuminating it’s like a Rorschach test. Some papers and transcripts of meetings between scientists have focused on the science, others haven’t. Labeling a theory as controversial may mean that that its deeply flawed, but it may also mean that it makes people uncomfortable, and its disturbing the paradigm.
The idea that infections may cause mental illness is sort of an uncomfortable notion. Do you agree?
Yes it’s terrifying, however, it’s also a blessing because for some of the most serious mental illnesses, we still don’t have great treatment. Many people with schizophrenia do extremely well but only half are adequately treated. When it comes to depression, the picture is even worse. So while it’s scary, it’s also a good thing in that prevention could be really powerful and not that difficult to do.
What do you mean by prevention?
If we do are able to trace connections between infections and mental disorders we can try to address the infection before it happens. Something as simple as making sure that everyone gets their flu shot could go a long way because it could protect a lot of young children. Ideally we’d be able to identify the pathogen and devise a vaccine or another strategy to prevent the infection.
How much of our understanding of medicine is influenced by scientists?
People tend to conflate science and scientists, who are human beings. Science as a practice is very different from our idea of science as this inexorable march toward the truth—I don’t find it to be that at all. Looking at the history of medicine, I think it’s more accurate to say we’re slouching towards the truth. We’re trying to achieve the truth, but there are always a lot of side alleys.
So is the idea that infection causes mental illness something we knew and forgot?
Exactly. People have in the past discovered the infectious nature of some mental illnesses and for a time the theory will become predominant. People will subscribe to it; doctors will practice according to it. Then something else comes along and supplants it and then it becomes forgotten until the next time someone finds a very dispensable example of a disease. There was a time where a lot of psychiatrists were looking at theories of infection as causative of mental illness.
Medicine has drawn a strict boundary between physical and mental illness; you say the line is blurry. Why?
I think the line is very blurred. For me it’s only an existential question because I have no way of addressing it, but you could ask: did we draw the line because we needed it clinically? It was practical for doctors treating patients who had certain conditions to draw that line, but I think perhaps it’s grown into a habit of thought that is not necessarily supported by the facts. We see cases all the time where there isn’t a dividing line, disorders that have both psychological and mental symptoms. Dividing them into physical and mental might be pragmatic, but it doesn’t mean that that dividing line really exists.
You mention that there are everyday examples of how the mental and physical overlap when it comes to being sick. Can you elaborate?
One expert neuroanatomist I spoke to who wrote a book on this calls it “sickness behavior.” A set of behaviors you see in people and animals that are infected. They tend to do the same things—which makes sense metabolically. If you have an infection not only do you feel depressed, but you tend to want to go to bed, shun social contact. In the animal kingdom it makes sense; a weakened animal is going to want to go away from contact and try to avoid predators until they’re feeling better.
With the growing chorus of voices supporting this, where do you think we go from here?
I think it’s impossible to predict how quickly things are going to progress and how much fruit it’s going to bear but I cant help but think that we may be approaching some sort of critical mass. We’re starting to see clinicians and researchers accept this new paradigm and accept that it does not displace our old ideas about mental illness. Stress is still important, genetics are still important, all of these things are important contributors to mental illness; but so is infection, it has a role too.