Germs spread by ticks and cats found in suicidal youth

Suicide tragically cuts more than 700,000 lives short each year. It ranks as the third leading cause of death among individuals between the ages of 15 and 29.

Taking one’s own life is antithetical to the drive of self-preservation, which confuses those who have never experienced thoughts of self-harm. This prompts many people to adopt a blame-the-victim mentality, which overlooks the biological bases that underlie suicide.

The notion that some suicides might be caused by an infectious agent is not new. People exhibit what researchers call “sickness behavior” while battling infection. The symptoms parallel many that are also seen in depression, such as social isolation, fatigue, and a gloomy disposition. One study found that individuals hospitalized with a serious infection were at a 42 percent higher risk of dying by suicide.

I’m a professor in the Department of Microbiology and Immunology at the Indiana University School of Medicine. My research focuses on infectious diseases and their contribution to behavioral changes in patients.

A new study finds a parasite and bacterium in suicidal youth

A 2026 study led by Edward Breitschwerdt, a professor of medicine and infectious diseases at North Carolina State University College of Veterinary Medicine, sought to marshal evidence that infectious agents may factor into suicidal behavior.

The research team conducted a postmortem analysis of six individuals aged 14 to 30 who had an unexplained chronic illness and suicidal behaviors. DNA testing was used to determine whether they were infected with Babesia, Bartonella, or Borrelia. While none of them showed evidence of Borrelia, five of the six tested positive for Babesia, Bartonella, or both.

Borrelia burgdorferi is the bacterium transmitted by deer ticks that causes Lyme disease. While these patients did not test positive for Lyme disease, it has been implicated in adverse mental health events. One study found that people with Lyme disease had a 28 percent higher rate of mental disorders and were twice as likely to have attempted suicide after infection.

Babesia is an emerging protozoan (single-celled) parasite transmitted by deer ticks. As the parasites infect and destroy red blood cells, they cause babesiosis. As bad as that sounds, most healthy people do not experience significant symptoms. The elderly, those who are immunocompromised, or people who have had their spleen removed—the organ that clears infected blood cells—can experience flu-like symptoms or more severe conditions such as hemolytic anemia. The type of Babesia species also dictates severity of illness. Babesiosis is treatable with drugs like atovaquone or azithromycin.

Bartonella is a bacterium that causes cat-scratch disease/fever. Infected fleas deposit the bacteria in their feces onto a cat’s fur. When the cat scratches or grooms, Bartonella can get into their mouth or claws. If the cat licks or scratches a person, Bartonella bacteria can transfer to them. Cat-scratch disease usually causes mild symptoms such as fever, headache, fatigue, and skin bumps. In severe cases, it can cause hallucinations, heart problems, or swelling of the liver and spleen. Minor cases resolve on their own within weeks, but more severe cases may require antibiotics like azithromycin.

Infections like those caused by Babesia or Bartonella trigger inflammation, a possible mechanism leading to changes in mental health. This “inflammation hypothesis of depression” is being examined; a recent clinical trial found that an anti-inflammatory medication reduced depression.

Limitations of the study

The study of human behavior is challenging because a single cause rarely explains a person’s actions. Suicide has genetic, psychological, and environmental components that are not mutually exclusive. Studies reporting an infectious agent in a suicidal person do not necessarily mean that it’s a driver of their behavior. For example, people who are suicidal may behave in ways that make them more likely to pick up an infection.

In other words, these studies are merely correlational—they do not establish causation. For an amusing lesson about the dangers of drawing conclusions based on correlations, check out “How Hall & Oates Have Ruined Everything.”

Breitschwerdt’s study is also limited to six people, a very small group. We do not have a good sense of how prevalent Babesia and Bartonella may be in people who do not experience suicidal ideation. Also, as mentioned, they only tested for three microbes. The rationale to focus on understudied microbes is reasonable, but it means that these patients could have had other infections that contributed to mental disturbances.

For example, Breitschwerdt’s study did not test for Toxoplasma gondii, a common parasite found in cat feces and contaminated food or water. Toxoplasma is estimated to have infected a staggering 30-50 percent of the world and is not eradicated from the body, as it establishes a chronic latent infection in the brain. Chronic toxoplasmosis has also been linked to persistent neuroinflammation, behavioral changes, and neurological disorders, including schizophrenia and suicide.

Given that so many carry Toxoplasma but do not have overt mental health issues suggests there is more to the story. It seems toxoplasmosis affects mental health more profoundly in a limited subset of infected individuals through a mechanism that remains unresolved. The same may be true of Babesia and Bartonella.

In short, observational reports such as this are intriguing but highly preliminary. They suggest that larger studies are warranted, as is research into how these pathogens persist and potentially affect the brain.

How to prevent tick-borne infections

While the jury is still out on whether Babesia or Bartonella directly affect mental health, it is nonetheless advisable to avoid these pathogens by taking the following precautions.

To reduce the risk of tick bites, use an insecticide containing DEET or picaridin. Wearing light-colored clothing can help you spot ticks crawling on you. Ticks usually stay on the ground and prefer shady areas with high grass, so mow grass to below 2 inches and keep the yard free of debris, including leaves.

If you’ve been in an area where ticks might be present, it is a good idea to shower and inspect your body for ticks. Ticks should be removed promptly and carefully with tweezers, pinching as close to the skin as possible to prevent parts of the tick from being left behind. If a rash or flu-like symptoms develop in the weeks following a tick bite, seek medical attention.

How to prevent infections from cats

To minimize cat-scratch disease, do not handle feral, stray, or other unfamiliar cats. Make sure your cat is free of fleas and do not let it lick you, especially open wounds or sores. Keep your cat’s claws trimmed and wash your hands with soap and water after handling your cat. If a cat does scratch you, prompt cleaning and disinfection of the wound reduces the risk of bacterial transmission.

Infection with Toxoplasma can be avoided by promptly changing the litter box and washing hands with soap and water afterward. Cats that are kept indoors and never fed raw or undercooked meat are generally free of Toxoplasma infection. Be mindful that oocysts can also be found in the garden, yard, sandbox, or other areas a cat may defecate. Wash fruits and vegetables to avoid ingesting oocysts, even if grown in your own garden where cats might have access. Encysted parasites can be found in meats, so be sure to cook meat to a safe temperature (usually 165°F).

This article was first published by Psychology Today.

If you or someone you love is contemplating suicide, seek help immediately. For help 24/7, dial 988 for the 988 Suicide & Crisis Lifeline, or reach out to the Crisis Text Line by texting CONNECT to 686868 (Canada) or 741741 (US).