Runner up in the Cambridge Infectious Diseases Science Writing Competition
Rui Adele Wang
Psychosis. Schizophrenia. Madness. What images do you see? For many, words like these conjure up thoughts of unwanted voices in the head, straight‐jackets, perhaps Russell Crowe in A Beautiful Mind. For many, these images will seem very far removed from the normal scenes of everyday life – traffic jams, supermarkets, picking up the kids from school. Indeed we cannot be blamed for thinking about schizophrenia in the context of out‐of‐the‐ordinary situations, since the symptoms themselves are usually out of the ordinary – hallucinations, paranoid thoughts, feeling like one’s own body is being controlled by some outside force. Therefore, it may come as a surprise that such an illness can stem from a common physical illness, the symptoms of which we are all familiar with ‐ flu.
Now there’s no need to panic as you sit reading this article, cup of Lemsip in hand, box of tissues to your right; it is not exactly flu itself that is the potential cause of psychosis. Rather researchers have found that mothers who are exposed to the flu virus during pregnancy give birth to children who are more likely to develop schizophrenia later on in life compared to children whose mothers who did not get flu. More specifically, in 2004,
Brown et al. found that children of mothers exposed to the influenza virus in the first half of gestation were 3 times more likely to develop schizophrenia than children of mothers who were not exposed. Even more shocking was the finding of a massive 7‐fold increase of risk to schizophrenia in the children of mothers who were exposed to influenza in the first trimester of pregnancy. This evidence was found using sample measures of the mothers during pregnancy, followed by clinical diagnoses of the children of the mothers in the experimental group, when the children reached the age of risk for schizophrenia. This connection between schizophrenia and flu exposure was further supported by preclinical evidence which observed the behaviour of rodent offspring of mothers who were injected with the influenza flu when they were pregnant.
And the link between prenatal infections and schizophrenia doesn’t stop there. Studies have also shown that mothers testing positive for Herpes Simplex Virus Type 2, HSV‐2, during pregnancy had a 1.6 fold increase in risk of giving birth to a child who would later develop psychosis (a term which includes schizophrenia, depression and bipolar disorder), with a 1.8 fold increase when specifically looking at risk of schizophrenia. The study suggested pregnant women who had previously been infected with the virus and who were in conditions which increased their chance of re‐exposure to the virus had an increased risk of schizophrenia in their children. This suggestion was supported when they found that the offspring of mothers who did not have a history of contraceptive use, and who reported a high frequency of intercourse during their pregnancy, were four times more likely to develop schizophrenia. Further research, however, needs to be conducted in this area, using more precise and direct methods of data measuring.
Outside of pregnancy, some infections which occur in childhood and adulthood also have a risk of causing psychosis and other mental illnesses. Children who become infected with serious central nervous system viruses, such the mumps virus, have an increased risk of schizophrenia later on in life. Lyme disease, a bacterial infection spread by infected ticks, affects the nervous system and has been known to cause a number of mental illnesses including psychosis.
The figures presented in this article must seem frightening. But it must be emphasized that these elevated chances of risk are still just that – chances of risks. Rather than causing panic, these results merely present another reason for maintaining one’s health which everyone should be taking care of anyway. The most important thing about these results is that it brings us closer to finding exactly why and how mental illnesses like schizophrenia are caused. This will in
turn bring us closer to finding cures and better treatments for such a disruptive and debilitating illness. One study, using an attributable proportion method, estimated that if infection of flu, herpes virus and T. gondii parasite had been entirely eliminated from the pregnant population of women sampled, approximately one third of schizophrenia cases in the children could have been prevented. 
So it seems that mental illnesses with so out‐of‐the‐ordinary symptoms can indeed have a root as common as the well‐known flu. It can be easy to dissociate illnesses such as schizophrenia with normal everyday life but, as we
are slowly discovering, the connection is not as distant as a lot of us think. This is just,another example showing us the importance of research, not only specifically for that particular field, but for implications across fields of medicine and science.
Serologic Evidence of Prenatal Influenza in the Etiology of Schizophrenia Brown, Begg, Gravenstein, Schaefer,Wyatt, Bresnahan, Babulas,. Susser Arch Gen Psychiatry. 2004;61:774‐ 780
Maternal Exposure to Herpes Simplex Virus and Risk of Psychosis Among Adult Offspring Buka, Fuller Torrey, Yolken, and the Collaborative Study Group on the Perinatal Origins of Severe Psychiatric Disorders Biol Psychiatry 2008;63:809–815
Infections in the CNS during Childhood and the Risk of Subsequent Psychotic Illness: A Cohort Study of More Than One Million Swedish Subjects Dalman, Allebeck,Gunnell, Harrison, Kristensson, Lewis, Lofving, Rasmussen, Wicks, Karlsson Am J Psychiatry 2008; 165:59–65
Lyme Disease: A Neuropsychiatric Illness Fallon, Nields Am J Psychiatry 151:11, 1994 pp.1571‐1580
Prenatal Infection and Schizophrenia: A Review of Epidemiologic and Translational Studies Brown, Derkits Am J Psychiatry 2010; 167:261–280