Toxoplasma gondii parasite linked to cancer cause

Toxoplasma gondii parasite linked to cancer cause

T. gondii, a parasite found in domestic cats, has now been linked to an increased risk of glioma, a brain cancer. It is possibly linked with other cancers such as lung, cervical and endometrial cancers.

Toxoplasma gondii is a parasitic protozoan (a single cell microscopic animal) that causes the disease Toxoplasmosis. The parasite is found in humans worldwide, although it is more common in developed countries. The reason for this is that, although it is found in foods, in water and in the soil, it is commonly found in domestic cats. Although it is capable of infecting any warm-blooded animal, domestic cats are the only known animal host in which the parasite can multiply (1).

Preventing infection from food and drink means observing basic health principles – avoid drinking untreated water, wash vegetables and fruit thoroughly and avoid undercooked meat (especially pork) and seafood. The contamination is due to oocysts. Cats consuming just one cyst can produce thousands of oocysts and this is why the CDC suggests pregnant women or people with an impaired immune system do not clean cat litter trays.


This disease in humans, although parasitic may carry no outward symptoms; possibly a slight fever with the first week of infection. According to the Mayo Clinic, infants born to infected mothers or people with compromised immune systems (for example, people with HIV) can have ‘severe complications’.

Toxoplasmosis and cancer

In a meta-analysis of 57 studies (3), cancer patients were observed to have significantly higher levels of T. gondii infection than controls; the odds ratio of cancer patients overall was 3.1 times higher in cancer patients, with women (40%) higher than men (37%).

In a 2015 study in China (4), the highest presence of T. gondii infection was detected in lung cancer patients (60.94%), then cervical cancer (50.0%) then brain cancer (42.31%) and endometrial cancer patients (41.67%).

The key question to answer is, ‘Is the infection causal of cancer in some way, or is it more reflective of the lowered immune system?’ 

In rats living in proximity to cats, it has been observed (5) that infected rats (caused by cat urine) undergo epigenetic changes in their brain amygdala which results in behavioural changes. Widespread neurological changes and astrocyte modifications occurred.

Astrocyte inflammation is known to occur due to microbiome changes in brain cancer patients (6). Schizophrenia and Bipolar disorders have been linked to humans infected by T. gondii (7).

Two studies (8) reported in January 2021 and entitled ‘Toxoplasma gondii and the risk of adult glioma’ suggest that the parasite is causal. The researchers state “It is known that the parasite shows affinity to neural tissue and may lead to the formation of cysts in the brain. Previous epidemiological studies have suggested an association between glioma and increased prevalence of T. gondii’.

The research analysed data from 700 people – almost equally split between infected and controls. The researchers measured antibodies to two T. gondii antigens and concluded with a 95% confidence that the T. gondii was increasing the risk of Glioma.

Go to: American Scientist finds Lyme disease parasite in brain cancer patients



  1. CDC – Toxoplasmosis (
  2. Mayo Clinic – Toxoplasmosis (
  3. Microbial Pathogenesis; Vol 129; April 2019, 30-42 (
  4. Wei Cong et al; Cancer Letters, 2015, 359 (2) (
  5. Hari Dass SA, Vyas A; Molecular Ecology, December 2014 (
  6. Microbiome affects brain astrocytes (
  7. De Barros et al; J Affect Disorder; 2017 Feb (209) (
  8. James M Hodge, Anna E Coghill; International Journal of cancer; 11 Jan 2021 (


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2021 Research
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