Toxoplasma gondii is a parasitic protozoan that causes toxoplasmosis, a disease that can infect most warm-blooded animals, including humans. It is one of the most common parasites globally and has a complex life cycle, primarily involving cats as its definitive hosts.
The parasite Toxoplasma gondii could be the star in a Hollywood science fiction film. One-third of the world is infected with it, though it rests dormant in most people. The tomcat outside may have it. You may have it. And it could drive you crazy.
Dr. Teodor T. Postolache, a professor at the University of Maryland School of Medicine, has extensively studied the link between Toxoplasma gondii (T. gondii) infection and suicidal behavior. Dr. Postolache's work throughout last 15 years has been instrumental in uncovering the potential impact of T. gondii on mental health and behavior, prompting further research into the parasite's role in psychiatric and age-related conditions.
In 2009, Dr. Postolache's team was the first to report a connection between T. gondii and suicide risk.
A 2012 study led by Dr. Postolache linked the parasite to intermittent explosive disorder (IED)—a condition characterized by repeated episodes of extreme rage.
The research, which analyzed data from over 45,000 women in Denmark, found that women infected with T. gondii were at an increased risk of attempting suicide.
Dr. Postolache, an expert in suicide neuroimmunology, was the senior author of the study, which was published in the Archives of General Psychiatry.
In a comprehensive 2021 review, Dr. Postolache and colleagues examined studies spanning 15 years, consistently finding a positive link between T. gondii IgG seropositivity and suicide attempts. The review highlighted that individuals with T. gondii infection had an increased risk—ranging between 39% and 57%—of attempting suicide. The paper also explored potential mechanisms, suggesting that the parasite may influence intermediate phenotypes such as impulsivity and aggression, which are associated with suicidal behavior.
T. gondii IgG refers to Immunoglobulin G (IgG) antibodies produced by the immune system in response to an infection with Toxoplasma gondii.
In 2023, Dr. Postolache co-authored a study investigating the relationship between T. gondii infection and frailty in older adults. The research found a significant positive association between T. gondii IgG serointensity and frailty, even after accounting for age and other confounding factors. This study suggests that chronic T. gondii infection may contribute to age-related health issues beyond its previously identified behavioral effects.
How Is Toxoplasma gondii Transmitted?
Ingestion of Contaminated Food or Water
Eating undercooked or raw meat (especially pork, lamb, or venison) containing cysts.
Drinking contaminated water.
Cat Feces (Oocysts in the Environment)
Cats infected with T. gondii shed oocysts in their feces, which can contaminate soil, water, and food.
People can get infected by handling cat litter, gardening, or consuming unwashed fruits and vegetables.
Congenital Transmission (Mother to Fetus)
If a pregnant woman gets infected, the parasite can cross the placenta and cause congenital toxoplasmosis, leading to serious birth defects or miscarriage.
Blood Transfusions or Organ Transplants
Rare, but possible if the donor is infected.
Symptoms of Toxoplasmosis
Most healthy people don’t show symptoms because the immune system keeps the parasite in check. However, when symptoms appear, they may include:
Flu-like symptoms (fever, muscle aches, fatigue)
Swollen lymph nodes
Headaches
Vision problems (if the infection affects the eyes)
Severe complications in immunocompromised individuals (e.g., those with HIV/AIDS or undergoing chemotherapy), leading to brain inflammation (encephalitis), seizures, or death.
The toxoplasmic trophozoites causing acute toxoplasmosis are referred to as tachyzoites, and are typically found in various tissues and body fluids, but rarely in blood or cerebrospinal fluid.
Prevention Tips
Cook meat thoroughly (internal temperature of 165°F or 74°C).
Wash hands after handling raw meat, soil.
Avoid unpasteurized dairy products.
Wash fruits and vegetables before eating.
Reducing the risk of T. gondii passing from a cat to their owner
The risk of getting toxoplasmosis from a cat is small, and living with a cat doesn’t put you at increased risk.
With some simple, everyday hygiene measures in place, you can reduce the risk of infection (from cats and other sources).
Here are some recommendations to reduce the risk of infection:
People in ‘high-risk’ groups (eg, pregnant women, immunosuppressed people, young children) should not have contact with or handle the cat’s litter tray
Empty litter trays daily, so that eggs don’t have time to sporulate (become infective)
Wear gloves when handling cat litter and wash hands thoroughly after cleaning the litter tray
Use litter tray liners if possible and periodically clean the litter tray with detergent and scalding water (which kills eggs)
Dispose of cat litter safely. For example, seal it in a bag before putting it with other household waste
Cover children’s sandpits when not in use to prevent cats from using them as litter trays
Feed only properly cooked food or commercial cooked cat food to your cat
Gloves should be worn when gardening and hands washed thoroughly after contact with soil which may contain infectious eggs
Fruit and vegetables should be washed before eating
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