Children with cats are more than twice as likely to develop schizophrenia, researchers say

Researchers from the Park Center for Mental Health, Australia, have added to the growing body of evidence that cat ownership is a major risk factor for schizophrenia and quantified the risk at more than double.

In an article entitled “Cat Ownership and Schizophrenia-Related Disorders and Psychotic-Like Experiences: A Systematic Review and Meta-Analysis”, published in Schizophrenia Bulletinthe team details the links between cat ownership among young people and schizophrenia-related diagnosis later in life.

The researchers conducted an extensive search of various databases and gray literature from January 1, 1980 to May 30, 2023, without geographic or linguistic limitations. They included studies reporting original data on cat ownership and schizophrenia-related outcomes. Of 1,915 studies identified, 17 were used in 11 different countries.

Cat ownership was associated with an increased risk of schizophrenia-related disorders. The overall unadjusted odds ratio (OR) was 2.35 and the adjusted estimate was 2.24, indicating a two-fold increase in the risk of developing schizophrenia-related disorders among all individuals exposed to cats.

Although some studies suggest that exposure to cats during childhood may be associated with an increased risk of developing schizophrenia-related disorders, the exact age or specific period of exposure is not clearly defined in all studies. studies.

A study included in Finland initially reported higher scores on the perceptual aberration, schizoid, and social anhedonia scales for people exposed to cats younger than seven years, although they limited their finding to the perceptual aberration. Another study conducted in the United Kingdom found associations between exposure to cats during childhood (at ages 4 and 10) and higher psychotic experiences at age 13.

Research suggests that the critical window of exposure needs to be better defined and could be influenced by various factors. Further investigation is needed to accurately identify the specific exposure period that may pose the highest risk of schizophrenia-related disorders associated with exposure of young cats.

The overall risk trend focuses on the interaction between brain development and feline exposure. But of course, it’s not just hanging out with feline personalities that’s responsible for the higher risk. There is a causal agent acting invisibly in the cat’s environment that is probably the real culprit: Toxoplasma gondii.

Toxoplasmosis

Toxoplasma gondii (T. gondii) is an intracellular protozoan parasite that causes toxoplasmosis, an infection that approximately 25% of the world’s population has contracted at some point.

This is why cat litter bags have a warning label for pregnant women to avoid contact with cat feces, as toxoplasmosis infection is the leading cause of neonatal blindness worldwide , as well as subsequent vision loss, mental disability and seizures.

Toxoplasmosis can be a significant cause of death in people with severely weakened immune systems. A drug is taken daily by AIDS patients, undergoing organ transplants or undergoing intense chemotherapy treatments, simply to counter the effects of this parasite.

T. gondii has previously been linked to all sorts of neurological impairments and behavioral changes, from guilt issues to novelty seeking and increased car accidents. Some manifestations of schizophrenia can be reversed by antiprotozoal medications, suggesting that T. gondii infection may have caused the symptoms in these cases.

A 2012 meta-analysis of 38 studies, “Toxoplasma gondii and Other Risk Factors for Schizophrenia,” also published in Schizophrenia Bulletinfound that patients with schizophrenia were nearly three times more likely to have antibodies against toxoplasma in their blood, suggesting that previous infections were much more common with this condition.

A striking finding of this study, when comparing risk factors for schizophrenia, was the discrepancy between the risk associated with having a first-degree relative with schizophrenia (RR 6.99 to 9.31) and the risk associated with specific genetic polymorphisms (OR 1.09 to 1.24). . Although a pattern of familial disease may suggest the involvement of shared genes, it may also indicate non-genetic factors such as environmental exposure to an infectious agent, such as a chemical superfluous site, or cats.

Toxoplasmosis has also been linked to various wildlife diseases, as behavioral changes in wild animals often result in poor survival strategies. Rats, for example, are no longer afraid of cats when they are infected. It is a common comorbidity in most California sea lions found in distress or dead from having a toxoplasma infection. If anyone is wondering how a sea lion comes into contact with a cat, try viewing a sandy beach from a cat’s perspective. That and the human habit of throwing away cat litter have created a huge problem for marine mammals.

Why cats?

The connection to cats is due to T. gondii’s affinity for reproducing only in domestic cats. This affinity may be linked to the absence of a single enzyme in feline intestines, delta-6-desaturase.

Although any mammal can be infected with the parasite, the digestive enzyme delta-6-desaturase prevents the parasite from obtaining high enough levels of linoleic acid that it needs to fuel its reproduction.

Unlike all other mammals, cats are full of linoleic acid because they do not produce the data-6-desaturase enzyme which would convert linoleic acid to oleic acid. Thus, the parasite only reproduces in the intestines of cats.

Cats then release oocytes (protozoan parasite eggs) by the millions when they defecate, trapping them in their fur and paws used to dutifully conceal their deposit, following them wherever a cat’s paw may wander.

Because the parasite has completed its life cycle, it may not affect the rest of the cat’s biology. In humans and other animals, the inability to transform into a larger reproductive form allows the tiny parasite to migrate beyond the blood-brain barrier, where the disruption occurs.

The missing enzyme and independent social lives of outdoor cats, mingling in shared sandboxes and soft garden soils around the world, make contact with cats the primary vector of infection. The secondary vector would be anything that has been in contact with a cat, such as a kitchen counter or any surface that a cat has walked on or rubbed against.

Even though social media has made it clear that society will collapse without cats, it is important that all cat owners never leave their cats outside in order to prevent the continued spread of the T. gondii parasite.

It is even more important that parents, with or without cats, understand the danger that cat-borne parasites can pose to their children’s long-term mental health.

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