There Is an Odd Link Between People Who Get Bitten by Cats And Depression

There’s some connection between cat bites and mental illness—it’s just not clear what it is

Photo: H. Guérault

Data mining sometimes reveals strange or unexpected patterns. Take, for instance, the recent discovery that people who come to the hospital to get treatment for a cat bite also tend to suffer from depression. From 1.3 million patient records that spanned 10 years, researchers found that 41 percent of of the 750 people who had cat bites also had been dignosed with depression. In comparison, they found that just 28 percent of the 1,100 or so people with dog bites were also depressed. 

The correlations don't stop there. Of those depressed, cat-bitten patients, 85.5 percent were female, compared to just 64.5 percent of depressed, dog-bitten people. After running some stats on the data, the team found that, "The probability of a woman being diagnosed with depression at some point in her life if she presented to our health system with a cat bite was 47 percent, compared to 24.2 percent of men presenting with a similar bite."

So what is going on here?

It's impossible to tell, really. But the team does have some guesses. As Popular Science writes, it could be that people who are depressed are simply more likely to own cats. On the other hand, it could be that depressed people are behaving in some particular way that a lot of cats do not like, triggering the bite themselves. Finally, it could be that depression is one more disease that falls under the "growing evidence" that there is a "relationship between cats and human mental diseases," the authors write. In particular, this refers to the parasite Toxoplasma gondii, which cats are a natural host to. Humans infected with T. gondii—which is transmitted through feces, not bites—are more likely to commit suicide, for example. There is also evidence that the parasite might play a role in bringing on schizophrenia in some people. 

For now, however, the significance of the connection with depression—if it means anything at all—remains a mystery. The authors do suggest that it might be worthwhile to screen women who come into the hospital with a cat bite for depression, which could help encourage them to get treatment for more than just the bite. 

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