Schizophrenia cases could be avoided if it were possible to avoid parasite infection, says

Publicação: 6 de January de 2015

Parasite proliferation, which is also linked to other mental disorders, is more common in the tropical countries

Around 20% of the schizophrenia cases among North-Americans could involve Toxoplasma gondii. In the poorest countries, this rate tends to be even higher

About 30% of the world’s population is infected by one of the most intriguing parasites known to scientists, the Toxoplasma gondii. Despite harmless for most of the healthy people, scientific researches have proven the protozoa is capable of changing the behavior of human beings and animals, besides a possible link to schizophrenia. Recently, an American study suggested that 20% of the schizophrenia cases among North-Americans could involve the parasite. In the poorest countries, this rate tends to be even higher.

The study, published on the Preventive Veterinary Medicine journal, was conducted by the veterinary doctor and professor Gary Smith, under the Epidemiology and Public Health topic from the Veterinary Medicine School of the Pennsylvania University. Smith managed to compute how important is the risk factor for the infection, which raises along with age.

“There are each time more evidences from studies that people infected by the Toxoplasma have an increased risk for schizophrenia”, explains the researcher. From this assumption, the challenge was to find out the proportion of mental disorders that could be avoided if the human infection by the parasite could be prevented.

From the calculations made by a computer software, this index would be fo 21.4% for countries as the USA and western Europe, where the incidence of T. gondii infections do not change along with age. “The result, however, would be different in many South American countries, since the non-incidence of the infection is clearly higher in the younger groups, especially among the poorest”, he said.

Brazil alone – the country with the largest infection rate in the world (66.7%), around 126 million people are hosts to the parasite. Its proliferation, by the way, is more common in tropical weather countries, especially in the poorest nations, where are great urban concentrations and no sanitation.

The disease is transmitted both by the ingestion of raw meat and infected land as through direct contact with cat secretion and feces. It could also be transmitted from mother to child through the placenta – it is recommended that pregnant women avoid contact with cats during the whole pregnancy. Despite being a common infection for humans and for animals, the Toxoplasma affects especially cats, the only beings where the parasite can reproduce.


Researches conducted in several countries have demonstrated how the T. gondii can be linked to neurological issues, as depression, especially among females. According to the article published on the Scientific American, one of these studies, conducted in the Stanley Medical Researches Institute, in Maryland, demonstrated that women infected with great amounts of Toxoplasma had a greater risk of having schizophrenic children.

Another paper, by Danish scientists had an even more alarming result. According to the research, women infected by the parasite were 54% more likely to attempt suicide. Generally, the attempts were violent, using cold and fire weapons. Among those with no history of mental illnesses, the index was also very high: 56% were more likely to attempt suicide.

The concern about the effects of this protozoa in the human body are also evident among mice. According to researches, the parasite can shift the behavior of these animals, making them for example, cease to be afraid of the smell of cats – some were even sexually attracted by the odor. Besides this, researchers found out that infected rats were able to recover the usual behavior using both anti-parasite and anti-psychotic drugs.

It has already been demonstrated that the infection increases the neurotransmitter known as dopamine levels, which is one of the factors for schizophrenia when found in high levels. This happens because the Toxoplasma has a gene that encodes a fundamental enzyme for the production of dopamine, and this is how they influence animal and human’s brains. Scientists, now, are trying to understand clearly how the parasite behaves in the brain.