Can owning a cat increase the risk of schizophrenia? The answer is yes, according to a recent review of 17 studies conducted by researchers from Harvard University University of Queensland in Australia.
The focus of the study
In their comprehensive analysis, the team conducted a meta-analysis of existing research, published over the past 44 years and covering 11 countries, including the United States and the United Kingdom.
What they discovered was that individuals who were exposed to cats before the age of 25 had almost twice the odds of developing schizophrenia.
Toxoplasma
The scientific rationale behind this association lies in a parasite called Toxoplasma gondii, or T. gondii for short, which is commonly found in domestic cats. This parasite has the ability to enter the human body through a cat bite.
Once inside, it can infiltrate the central nervous system and affect neurotransmitters in the brain. This, in turn, can lead to personality changes, the appearance of psychotic symptoms, and the development of psychiatric disorders, including schizophrenia.
Schizophrenia scale
One study included in the review, which focused on 354 students in the United States, found no direct link between cat ownership and scores on a schizotypy scale.
However, when comparing individuals who had been bitten by a cat to those who had not been bitten, the bitten group showed higher scores on the schizotypy scale.
This scale is essentially a questionnaire designed to measure traits associated with unconventional and disorganized thought patterns, which are often used in the diagnosis of schizophrenia.
Severe mental disorder
Schizophrenia is a severe and chronic mental disorder that affects an estimated one percent of the world’s population, with about two million people in the United States alone.
This condition profoundly affects how a person thinks, feels, and acts, often causing the affected individual to seem disconnected from reality.
The exact cause of schizophrenia remains elusive, with experts speculating that it may be a combination of genetic factors, abnormalities in brain chemistry, viral infections, and immune disorders.
Symptoms of schizophrenia
Symptoms usually appear between the ages of 16 and 30, although there have been rare cases of children also being affected.
Symptoms of schizophrenia can be classified into three groups: positive, negative, and cognitive.
Positive symptoms
Positive symptoms include disturbances that are “added” to an individual’s personality, and include hallucinations, delusions, and thought disorders characterized by unusual or dysfunctional thought patterns.
Negative symptoms
Negative symptoms include loss of certain abilities of one’s personality, such as “fixed affect” (decreased emotional expression through facial expressions or tone of voice), decreased pleasure in daily life, and difficulties initiating and maintaining activities.
Cognitive symptoms
Cognitive symptoms include changes in memory and other cognitive functions, including problems with concentration, attention, working memory, and the ability to understand information and use it to make decisions.
Study limitations
However, the University of Queensland review faced criticism on Twitter from other researchers who said it did not adequately take into account other potential contributing factors, such as socio-economic backgrounds and family history.
For example, a British study found an association between exposure to cats in childhood (between the ages of 4 and 10) and increased psychotic-like experiences at age 13, but these findings did not persist after adjusting for potential confounding variables.
Dr Sanil Rege, a Melbourne-based psychiatrist, noted that 15 of the 17 studies included were case-control studies known to be susceptible to spurious correlations.
The study is published in the journal Schizophrenia Bulletin.
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