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Autism and ADHD may be linked with the parasite Toxoplasma gondii


Toxoplasma gondii is the parasite that causes toxoplasmosis. This parasitical infection is largely asymptomatic, but its been known to cause chronic oxidative stress in the brain of the host, which plays an essential role in the pathogenesis of neurological disorders like autism and ADHD.


This has been further discussed in a recent review that suggested there is a correlation between Autism and the reactivation of latent toxoplasmosis, which can be caused via environmental triggering factors like pregnancy, viral/bacterial infections, vaccinations, medications, and other substances. The profuse multiplication of Toxoplasma gondii in the brain is associated with persistent neuro-inflammation. It also causes chronic overproduction of pro- inflamatory and antiinflammatory cytokines and nitric oxide, which increases oxidative stress in the parasite host.

In what way does Toxoplasma gondii causes disruption in the neurological system?

1)It affects testosterone production

The neurological aspects of a toxoplasmosis infection have been detailed in many studies that demonstrated that toxoplasmosis, even in its latent stage, can induce different hormonal and behavioral and cognitive alterations in humans and rodents. There have also been reports of a significantly higher concentration of testosterone in women with latent toxoplasmosis.

Interestingly, several complex neuro-developmental disorders may be associated with higher levels of testosterone, including antisocial, aggressive behavior and ADHD symptoms. Correspondently, some of these neuro-developmental disorders have been reported in individuals with latent toxoplasmosis and ASD probands.

2) It affects the size, function of areas of the brain responsible for behaviour and cognition.

A research on The Distribution of Toxoplasma gondii Cysts in the Brain of mice with latent toxoplasmosis, revealed the areas of the brain that were mostly infested corresponded to the olfactory bulb, the entorhinal, somatosensory, motor and orbital, frontal association cortex and visual cortices, and, importantly, the hippocampus and the amygdala. All brain regions that are responsible for behaviour and cognitive skills. These affected areas have been shown to either be of abnormal size or function abnormally in ADHD patients.

It is know that connectivity of these prefrontal regions, especially the ventromedial prefrontal cortex, with the hippocampus and amygdala regulates a variety of attentional, memory, and emotional. Circuits connecting the amygdala and orbitofrontal cortex (OFC) support decision - making and reward reinforcement. So, disturbances of these circuits cause behavioral disinhibition and impulsivity.

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3) It affects the connectivity between neurons

It is well established by the scientific community that parasitical infestations that cross the blood brain barrier disrupt neurotransmitter pathways. A recent article on the Toxoplasma gondii and its implications in many neurological disorders, explained that to be infected with this parasite, affects the Erbb signaling networks, which regulate the assembly of neural circuitry, myelination, neurotransmission, and synaptic plasticity. The myelination of cells, is a highly relevant process to a number of psychiatric disorders such as autism and ADHD. It consists in the process of coating the axon of each neuron with a fatty coating called myelin, which protects the neuron and helps it conduct signals more efficiently.

An investigation based on a possible pathological relationship of autoimmunity to autism found that 58% of the subjects involved had Myelin Basic Protein anti – bodies. This dysfunction implicates in a pathological effect of under connectivity between neurons, a pathological feature of autism.

4) It caused oxidative stress and changes the behaviour of the host

Myelin is sensitive to oxidative stress and glutathione depletion caused by oxidative stress. Glutathione is natural substance made from glutamate, and a recent study on rodents revealed that there is a significant reduction in the primary astrocytic glutamate transporter, GLT-1, following infection with Toxoplasma. The Glutathione precursor N-acetylcysteine, has been shown to be in involved in the pathogenesis of autism.

It has also been observed, through behavioural testing and Electroencephalography recordings, significant changes in neuronal output. Therefore following an infection with T. gondii, the delicate regulation of glutamate by astrocytes is disrupted and accounts for a range of deficits observed in chronic infection.

These changes in neuronal output transpire in behavioural outcomes for the host. This premise has been confirmed by a research on weather Toxoplasmosis gondii infections would indeed affect the behaviour of the host. Tests detected that the parasite has genes encoding tyrosine hydroxylase, a rate-liming enzyme of dopamine biosynthesis. While the encysted parasite expresses dopamine and enhances the K+ (potassium ion) induced release of dopamine from dopaminergic neurons. This implicates in a change of behaviour transpired by the hyperactivity of infected studied rodents, and altered novelty seeking behavior. Likewise, some studies discuss that there are implicated abnormalities of dopamine neurotransmission to the pathology of attention deficit hyperactivity disorder (ADHD).

Other behavioral studies have shown that latent toxoplasmosis is associated with impaired motor performance, deficits in spatial learning and memory, reduced anxiety, higher activity levels in both novel and familiar environments, sensory attention deficits, altered novelty seeking behavior and longer reaction times. These are the same neurotypical biomarkers analised to diagnose ADHD and Autism.

According to the Centers for Disease Control, more than 60 million men, women, and children in the U.S. carry the Toxoplasma parasite, and it is considered to be a leading cause of death attributed to foodborne illness. Toxoplasmosis infection has been correlated with many other pathological features of various neurological disorders like: alzheimers, OCD, depression and anxiety.

Therefore, given the wealth of information on the effects on the neurological system of animals and people infected with toxoplama gongii, it would be wise to be screened for toxoplasmosis via a blood test if you or your child, has been diagnosed with Autism, ADHD or any other neurological disorders. This parasite can be caught if you have been in contact with cat faeces, contaminated soil, unwashed contaminated vegetables or have eaten infected animals.