More Evidence Links ‘Cat Scratch’ Bacteria and Schizophrenia

New research is the latest to find evidence of a link between mental illness and infections caused by a group of bacteria commonly found in cats and other animals. The small study found that people with diagnosed schizophrenia and schizoaffective disorder were more likely to carry Bartonella bacteria in their bloodstream than a control group of patients. More research is needed to definitively show whether these infections can indeed contribute to mental illness, however.

Acute infections involving Bartonella bacteria can be especially serious for people in poor health or with weakened immune systems. In most people, it’s thought they only cause mild and short-lasting illness. For years, though, Ed Breitschwerdt and his fellow researchers at North Carolina State University have theorized that the health effects of these infections can run deeper in at least some unlucky people.

Their previous work has highlighted the case of a 14-year-old boy who suddenly developed schizophrenia-like symptoms and was later found to carry a species of Bartonella known for causing cat-scratch fever. In that case, the boy’s severe psychiatric problems seemed to clear up once his chronic Bartonella infection was treated with antibiotics. Last year, they published research finding that other people with similar neuropsychiatric symptoms often carried these bacteria, along with physical symptoms of an ongoing infection that appeared around the same time, such as distinct skin lesions.

For this new research, the NC State researchers worked with researchers from the University of North Carolina. Their study, published last week in Vector-Borne and Zoonotic Diseases, compared 17 people with diagnosed schizophrenia or schizoaffective disorder to a control group of 13 healthy people, in what’s known as a case-control study.

According to the study, both groups were given a comprehensive examination. This included the use of more sensitive PCR testing, which looks for the DNA presence of pathogens in our body. Bartonella are somewhat odd among bacteria, since they’re capable of infecting and then hiding inside our body’s cells (red blood cells, in the case of Bartonella). This disappearing trick allows them to survive undetected from the immune system, and it also makes conventional tests worse at spotting an active infection. Last year, Breitschwerdt and his colleagues published research showing that this newer testing technique, called droplet digital, or ddPCR, testing, could be more accurate at identifying Bartonella than older tests.

In 11 of the 17 people with schizophrenia or schizoaffective disorder, traces of Bartonella DNA could be found, while the same was only true for one of the 13 control patients. Though cats, dogs, and even the fleas they carry can possibly be vectors for Bartonella transmission, the team didn’t find any link between a higher chance of infection and reported pet ownership or flea exposure.

The team is careful to describe their work as a pilot study, solely meant to prove that further investigation into this link is worthwhile. But coupled with their earlier research, Breitschwerdt believes the case for this theory is only getting stronger.

“Our research to date continues to support a role for Bartonella species as a cause or co-factor in neuropsychiatric illness,” Breitschwerdt told Gizmodo in an email.

However, he added: “There is a lot of work that needs to be accomplished to clarify these preliminary results.”

The team is already working on validating ddPCR testing for other groups of bacteria that can invade the bloodstream and may be harder to find with standard testing. With more funding and cooperation with other research centers, they also hope to carry out a larger study comparing people with and without schizophrenia.