Study suggests parasite in bad meat affects memory and learning YEARS after you're sickened

As if the diarrhea and vomiting wasn't punishment enough - researchers now think a bout of food poisoning could make you less intelligent in the future. 

If you've had food poisoning before, you're more likely to have poor learning skills, poor memory and to develop schizophrenia, according to parasitologists and evolutionary biologists at Charles University in the Czech Republic.

Previous research has identified this link in the weeks and months after developing food poisoning. 

But scientists involved in these studies have attributed this to the fact that people simply don't feel themselves in the immediate aftermath of feeling sick.

Some of the early symptoms of food poisoning include vomiting and diarrhea, but long-term, some studies have shown that this parasite can lead to memory changes

But the new research suggests that the personality changes from food poisoning lasts well after you recuperate. 

The experts, from Charles University in Prague, focused on two specific bugs that impact a wide swath of the population, and can survive in the body for extended periods of time.

One, called Toxoplasma gondii, is responsible for 800,000 cases of food poisoning each year in the US. Toxoplasma can be found in all types of meat, but is particularly prevalent in pork, lamb and venison, according to the FDA.

The other, Borrelia spp, is a bacteria responsible for Lyme disease, which effects roughly 476,000 people each year in the US. 

Toxoplasma gondii is a parasite that can prey on many different types of hosts - from humans to cats, according to the CDC. Other than bad meat, it is found in contaminated water and sick cat poop.

Almost a quarter of people past adolescence said they caught the parasite, according to Dr. Jeffery Jones, an epidemiologist and pediatrician at the Centers for Disease Control. It causes roughly 24 percent of foodborne illness deaths in the US.

If you're healthy, then accidentally taking in some of this parasite will probably only cause a mild infection. 

The prevalence of toxoplasmosis in the US generally increases with age, according to Dr Michael Greger of Nutrition Facts. 

But if you're immunocompromised or pregnant, you might have an intense and sudden episode of vomiting, chills, diarrhea, sweating and weakness, in response to the parasite, according to doctors from Baylor College of Medicine. This might be why you see more Toxoplasma infections in the US as people age, according to Nutrition Facts. 

The parasite doesn't leave your body after you stop feeling sick, according to the CDC - it often stays in you for life. Most people will have very few noticeable symptoms, but if you're immunocompromised you may develop flu-like symptoms. 

The study, which was published in the journal Folia Parasitologica, surveyed 7,762 people with an average age of 42.

Roughly 962 of those people reported testing positive for Toxoplasma and 1,778 of those people reported having been infected with Borrelia.

Each of the respondents completed a barrage of tests designed to measure personality traits, memory and cognitive abilities.  

The people who had had food poisoning from toxoplasma before had slower reaction times and less accurate responses to a common neurological exam called the Stroop Test. 

A photo of the parasite toxoplasmosis under the microscope. You can get this from undercooked meat or infected cat poop

One common version of the Stroop Test involves participants looking at words of colors written in different colored fonts. For example, the word blue might be written in a green font and the word orange might be written in a pink font. 

The participants have to identify the color of the word, not the word itself. 

The Stroop test is used in labs as a measure of attention span, memory, mental sharpness and intelligence, according to Lesley University.

Generally, if the participants responses were slower or less accurate, the researchers denoted that as a sign that their memory or intelligence was poorer.

The study authors say their results indicated long-lasting effects of the infections, as  the changes in behavior didn't only occur in people who were in poor health due to the bug.

Participants still had worse memory even after their physical symptoms had resolved, the authors reported, which means that the parasite caused chronic problems.

Toxoplasma might affect your memory by changing the amount of neurotransmitters that your brain releases, one study suggests

A 2021 study of 800 adults in Taiwan found that people who got food poisoning from toxoplasmosis were 2.8 times more likely to develop dementia than those who didn't. In addition, people who were treated for the disease were less likely to develop dementia than those who were not. 

Also, rodents that have been infected with this parasite have been shown to have worse memory and a harder time navigating their enclosures,  according to a 2023 study from Pasteur Institute of Iran. 

The disease has also been linked to other neurological changes, like schizophrenia. A 2022 study from the Federal University of Rio De Janeiro fount that people who had been infected with toxoplasma were more likely to develop schizophrenia than people who hadn't got the parasite. 

Beside cat poop, the most common way that people get a toxoplasmosis parasite is from eating undercooked and infected meat 

Scientists aren't exactly sure how this parasite changes your brain. But one theory, explained in a 2023 paper from Ahvaz Jundishapur University of Medical Sciences in Iran, said that the parasite could alter the levels of chemicals in the brain that control mood, memory and emotion. 

The study found that exposure to toxoplasma caused an increase in a chemical called dopamine and a decrease in a chemical called serotonin, in the brains of rodents. This led to changes in memory and behavior.

Another theory is that the parasite living in your body long term can cause a small, but consistent immune response in your body, that over time, may wear down your brain, according to  Dr Michael Greger, a public health specialist and nutritionist. 

The researchers in the Czech study concluded that though these diseases seemed to be linked, they couldn't yet show how it did so.