Since domestic cats are the primary hosts of T. Gondii (i.e., they provide an environment within which this parasite can reproduce) some people have speculated that cat ownership may put people at increased risk of mental illness, by exposing them to T. Gondii infection. While a handful of small studies have found evidence to support a link between cat ownership and psychosis, most of these investigations had serious methodological limitations (e.g.: relying on recall of past cat ownership, small sample sizes, missing data, lack of control for other explanations), which may have biased their findings.
To tackle these limitations, we used data from a large, longitudinal sample of approximately 5,000 children, a sub-group of 14,000 children born in the former region of Avon, (UK) between 1991 and 1992. Unlike previous studies, we were able to follow people over time, from birth to late adolescence, and address a number of the limitations of previous studies, including controlling for alternative explanations (including socioeconomic status, ethnicity, other pet ownership and over-crowding) and taking into account missing data. We studied whether mothers who owned a cat: 1) while pregnant; 2) when the child was 4 years old; and 3) 10 years old, were more likely to have children who reported psychotic symptoms (e.g.: experiences of visual or auditory hallucinations, and of paranoia) in early (age 13) and late adolescence (age 18).
We found that children who were born and raised in households that included cats at any time period were not at a higher risk of having psychotic symptoms when they were 13 or 18 years old. This finding in a large, representative sample was robust against issues of missing data and alternative explanations. Although most people who experience psychotic symptoms in adolescence will not develop schizophrenia later in life, they can indicate an increased risk for such disorders.
It is important to remember that there is evidence linking T. Gondii exposure in pregnancy to risk of miscarriage and stillbirth or health complications in offspring. We therefore recommend that pregnant women should continue to avoid handling soiled cat litter and other sources of T. Gondii infection (such as raw or undercooked meats or unwashed fruit and vegetables). That said, data from our study suggests that cat ownership during pregnancy or in early childhood does not pose a direct risk for later offspring psychotic symptoms.
This month the PsyLife team attended the annual MQ Mental Health Science Meeting. Following on from MQ’s recent ‘We Swear’ campaign (right), the meeting was focused on the role of research in improving our understanding of the aetiology, treatment and prevention of mental health problems. The event was interdisciplinary with speakers and attendees including psychologists, neuroscientists, epidemiologists, clinicians, policy makers, and mental health service users united by a shared interest in mental health.
Several speakers presented findings about risk factors for mental illness. We heard from Professor Louise Arsenault and Dr Jean-Baptiste Pingault about the association between bullying victimisation and future mental health problems. Both talks were very interesting, and highlighted the need to focus on both the experiences of being bullied as well as predictors of bullying itself. We also heard from Professor Ezra Susser, one of psychiatry’s pre-eminent epidemiological thinkers, on his work examining the potential role of prenatal micronutrient deficiencies in neurodevelopmental disorders in offspring. Professor Susser highlighted the need for randomised controlled trials with long-term follow-ups, and/or the use of techniques such as Mendelian randomisation to further explore this topic.
Numerous talks focused on depression in young people. We heard about Professor Myra Weissman’s pioneering work showing the transmission of depression across three generations. Dr Frances Rice discussed antecedents of depression in at-risk adolescents and highlighted the importance of future studies examining the role of social support in this group.
Several talks demonstrated the role that neuroscience can play in improving our understanding of mental health problems and developing interventions. Dr Susanne Ahmari presented her work on the neural circuits underlying obsessive-compulsive disorder and how this could translate to future treatments. Professor Carmen Sandi discussed the impact of genes and environment on brain development, demonstrating that rodents exposed to early life stress showed structural and functional brain alterations and were hyper-aggressive later in life.
Professor Jonathan Mill discussed how epigenetic research could help to improve our understanding of mental illness, but also warned us not to believe all the media hype. To much amusement and shock from the audience, Professor Mill presented some of the media misrepresentations and pseudoscience surrounding epigenetics, including the advertisement of epigenetic spray and an epigenetic orthodontist!
It was interesting to hear several talks on psychosis from different perspectives. Professor Mary Cannon showed that children and adolescents who experience psychotic symptoms are at increased risk of developing future mental health problems, including schizophrenia, although these symptoms have a low positive predictive value and intervening early could therefore be problematic. Dr Graham Murray showed that, in people with chronic schizophrenia, the jumping to conclusions bias can largely be attributed to noisy decision making, whereas those with first-episode psychosis seem to genuinely jump to conclusions: perhaps due to perception of a high cost of gathering information.
Of great interest to our lab was Professor Andreas Meyer-Lindenberg’s talk on the relationship between the social environment and the brain. The talk focused on urbanicity and migrant status: two well-established environmental risk factors for psychosis identified in epidemiological research. Urban birth, urban living, and migrant status were found to be associated with structural and functional differences in brain regions implicated in social stress processing (such as the amygdala and the perigenual anterior cingulate cortex). These findings demonstrate how associations observed in epidemiological research can be further examined using psychology and neuroimaging techniques. However, participants in most of these studies were from the general population. It would be of great interest to see whether findings replicate in those with psychosis.
One further highlight of the conference was the thought-provoking panel discussion entitled ‘What good is a diagnosis?’. Megan Haste, a mental health blogger and service user, described the relief she felt when she was given a diagnosis, and Professor Susser pointed out that diagnoses can be helpful for constructing a personal narrative around mental health problems. However, he also discussed the challenges of using the same diagnoses across different cultures given cross-cultural variation in perceptions of mental illness. Professor Wessely highlighted the importance of diagnoses for providing appropriate treatments for patients, whereas Professor Wolpert suggested that it may be more beneficial to focus on a given patient’s symptoms and treatment needs, rather than categorisation.
The event also included a poster session where early career researchers presented work spanning a wide range of topics. I presented findings from a review of the incidence of very late-onset psychotic disorders, which I am carrying out as part of my PhD. This provided an opportunity to receive feedback on my work and to hear about current research on psychotic disorders, as well as other mental health problems, from across disciplines.
Overall, the meeting was a great opportunity to hear about some of the latest research targeting mental health problems in young people. The importance of addressing this issue is discussed from a clinician’s perspective by Dr Daria Monteforte, a psychiatrist from Verona currently on a research visit at PsyLife:
“As a medical doctor working in the field of mental health I really appreciated the choice of subject and the interventions discussed. It is now widely understood that psychiatric disorders often affect patients during youth, sometimes from childhood, and that only a small proportion of those in need are diagnosed and treated. A delay in intervention can undermine future opportunities for young people because of the destructive impact that mental health problems can have on many areas of life, including: building relationships, school, university, and career. More and more patients and their relatives are struggling with barriers to accessing services, diminishing resources in mental health services, and concerns about stigma. We work with many young adults who may have had a better prognosis if they had received the support they needed as children and adolescents. Research and discussion about mental health in young people helps us to understand the scale of the problem, what these particular patients need, and in which direction we should focus our efforts.”
Over the past few years, a number of scientific studies and media outlets have reported that Toxoplasma Gondii (T. Gondii) infection could increase a person’s risk of experiencing adverse mental health outcomes – including schizophrenia, suicide, and intermittent rage disorder.
