Toxoplasma gondii, a bacterial which can affect humans by eating infected pork, beef or poultry meat, has been probably linked to the existence of higher rates of brain cancer.
A team of scientists led by Frederic Thomas and Kevin Lafferty, Centre National de la Recherche Scientifique (CRNS), Montpellier, France, found that countries where more people are infected with the parasite have higher rates of brain cancer.
The team predicted that the common parasite T. gondii could increase the risk of brain cancer because it is a long-lived parasite that encysts in the brain, where it provokes inflammation and inhibits apoptosis. They used a medical geography approach based on the national incidence of brain cancers and seroprevalence of T. gondii.
The scientists corrected reports of incidence for national gross domestic product because wealth probably increases the ability to detect cancer. We also included gender, cell phone use and latitude as variables in our initial models.
They wrote: "Prevalence of T. gondii explained 19% of the residual variance in brain cancer incidence after controlling for the positive effects of gross domestic product and latitude among nations. Infection with T. gondii was associated with a 1.8-fold increase in the risk of brain cancers across the range of T. gondii prevalence in our dataset (4–67%). These results, though correlational, suggest that T. gondii should be investigated further as a possible oncogenic pathogen of humans."
Humans can become infected with T. gondii, either through contact with soil contaminated by cat faeces, or by eating infected meat. These infections are extremely common, and up a third of the world may carry the parasite. However, rates of infection vary greatly from country to country, from just 7% in the UK and 11% in the USA, to around 67% in Brazil.
The paper was published in Biology Letters.
• Biology Letters