When animals suffer from mental disorders
I know someone who has a dog that is on a 3 m long-chain 24 hours a day, almost the entire year. There is a small dog house that serves as a shelter and the dog gets its food and water regularly, but no cuddle, no pat, no bath ever. A dog’s life ?! It doesn’t surprise me that this dog obsessively runs around in a 2.5 m wide circle, sleeps a lot or is occupied tearing hairs out of its tail. I’d call that an “Obsessive Compulsive Disorder”, usually abbreviated OCD, an abnormal behaviour relatively easily recognizable in humans by psychiatrists. Since at least mammals and birds can suffer from physical troubles also affecting humans (e.g. bones, lungs, heart, brain, gut, etc.) the question arises if they cannot also suffer from mental illnesses.
Many years ago as a PhD-student in neuroscience I once had to translate a short manuscript for a medical journal. That manuscript dealt with a supposedly schizophrenic cat and described the symptoms that led the researcher to her conclusion. In humans, schizophrenia is characterized by hallucinations like hearing voices, by delusional beliefs, emotional remoteness, and an odd behavioural repertoire. To diagnose schizophrenia based on these symptoms in animals would be very difficult and it is commonly believed that animals do not really suffer from that disease and that certain portions of the DNA in humans, predisposing them for the disease, are missing in mammals. However, there is little objection to the view that other more easily identifiable mental disorders could also affect animals, especially domestic ones.
Post-traumatic stress disorder, known as PTSD, is characterized by recurring nightmares, severe emotional distress or strong behavioural reactions upon a reminder of the traumatic event and PTSD has been described, for example, in military dogs even after their ‘retirement’. I can add to this an observation on our cat that was once bitten by a large so-called bird-eating spider that the cat had decided to play with. The cat got very, very ill and my children feared it would die, but it didn’t. However, even one year later when presented with a rubber toy spider, the cat went into a frenzy, started vomitting and apparently ‘re-lived’ the traumatic event a year earlier. It was really amazing to watch suggesting not only that our cat had an excellent memory, but also associated an earlier traumatic event with the cause of its unwellness.
Depression and anxiety are mental disorders that affect large numbers of humans (and I am not only thinking of depressed students after a failed examination or students suffering from anxieties before an examination that they fear they might fail). These disorders have also reliably been described from cage birds as well as dogs and cats, especially after the loss of a partner or offspring. The big problem of making the correct diagnosis is that there are few genetic markers and that, of course, communication with animals is very difficult. With regard to physical illnesses, veterinarians find it far easier to find a cause than animal psychiatrists do (are there such people at all?) for mental or behavioural abnormalities.
We could even go a step further and ask ourselves if invertebrates cannot also suffer from delusions, OCDs or PTSDs, the latter perhaps after a narrow escape from the web of a spider. Apparently, most vertebrate pathologists would find agents of disease (e.g. bacteria, viruses, etc.) in animals like insects, spiders and crustaceans quite familiar and, indeed, all invertebrates can get sick like vertebrates and suffer from infections and even cancers. To fight diseases certain unifying principles are likely to have evolved in all animals, including invertebrates. But does that extend to mental disorders, psychotic diseases in invertebrates? Paranoia and abnormal anxiety in bumblebees, apparently exists and has been described. It seems I have just suggested an interesting research project: an investigation into possible mental disorders in invertebrates!
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2020.
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