Could cat-scratch disease be linked to schizophrenia? A pilot study has suggested that people with schizophrenia are more likely to be infected with Bartonella, the bacteria behind cat-scratch disease.
The research only involved a very small number of people, so the findings should not be overstated – but it could highlight an intriguing way in which infectious agents are linked to schizophrenia and other mental health issues. The findings were recently reported in the journal Vector-Borne and Zoonotic Diseases.
Researchers at North Carolina State University and the University of North Carolina carried out blood tests on 17 people with diagnosed schizophrenia or schizoaffective disorder, along with a control group of 13 healthy adults, to test for evidence of Bartonella infection. Out of the 17 patients with schizophrenia, 12 had Bartonella DNA in their blood, while evidence of the infection was found in just one person in the control group.
The nature of this possible link between infection and schizophrenia is not clear, since the study did not set out to find a causal link between the two. In other words, there’s no evidence the bacteria actually played a role in the development of schizophrenia. However, the researchers argue their preliminary findings open up an intriguing path for further inquiry
Bartonella is a common genus of bacteria that's transmitted by animal vectors such as ticks, fleas, sand flies, and mosquitoes. One of the most infamous species of this genus, Bartonella henselae, is the causative agent of cat-scratch disease, an infection spread by cats that infects over ten thousand people in the US each year. Most infections are mild, causing little more than a red injury site and swollen lymph nodes, but it can cause people to have serious complications including brain swelling. It’s also become increasingly apparent that Bartonella is not always a short-lived infection, and can continue to linger within some people.
The link between the infection and mental health has also been hinted at before. In March 2019, the same team of scientists published a case study where a case of sudden-onset adolescent schizophrenia was seemingly linked to a B. henselae infection. Their follow-up study looked at 33 similar cases where people had neuropsychiatric symptoms and suspected exposure to Bartonella bacteria. They found evidence of a previous or current Bartonella infection in 29 of the 33 people studied.
Once again, it should be stressed that larger and more refined studies are needed before any of these proposed links are nailed down. Nevertheless, the team certainly seems to think they’re on to something.
“Researchers have been looking at the connection between bacterial infection and neuropsychiatric disease for some time,” Dr Erin Lashnits, first study author, a former veterinary internist at NC State, current faculty member at the University of Wisconsin, said in a statement.
“Specifically, there has been research suggesting that cat ownership is associated with schizophrenia due to the zoonotic parasite Toxoplasma gondii, but to date there has been no conclusive evidence in support of a causative role for this parasite. So we decided to look at another cat-associated infectious agent, Bartonella, to see if there could be a connection.”