A common parasite that spreads through undercooked pork, and occasionally our cats can have more insidious health effects than previously suspected. New research suggests a link between infection with Toxoplasma gondii and an increased risk of brain cancer. At this point, however, scientists are not yet sure if there is a direct cause-and-effect relationship, and the overall risk of brain cancer is still very low.
T. gondii is known for his mind-altering rodent tricks, one of their natural intermediate hosts. In these animals, the single-celled parasites prompt them to become reckless in the face of danger, causing them to no longer avoid the smell of cat urine. The Redsts – and their parasites – are then more quickly devoured by a feline, allowing the parasites to reach their primary feline host and mature. They then incubate and create a new generation of eggs that are defecated by the cat in the environment, restarting the gruesome life cycle. Humans are an unfortunate bystander here, as they become infected either through close contact with cat poo or through eating meat (usually pork) contaminated with T. gondii cysts.
Acute T. gondii infections in humans can be serious for people with weakened immune systems or for newborns who contracted it in utero. However, in most people, an acute infection does not cause any symptoms, while a few may develop mild, flu-like symptoms for several weeks.
Historically, these acute symptoms were believed to be the extent of the damage T. gondii can cause us. But more recently, scientists have one intriguing connection between the parasite and subtle neurological effects in humans, aided by the fact that cysts can quietly survive for decades in the body, including the brain. Chronic T. gondii infections have been associated with an increased risk of schizophrenia, decreased cognition and behavioral changes such as increased risk taking and aggression. This new study, published in the International Journal of Cancer, indicates that certain types of brain cancer may need to be added to the above list.
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The researchers looked at data from research projects that track people’s health over time, including a long-term cancer prevention study conducted by the American Cancer Society. They specifically targeted people who were later found to have gliomas, the most common form of brain cancer. As part of their first study, the volunteers gave blood samples that were tested for antibodies to a variety of germs, including T. gondii.
When the researchers compared people who eventually developed gliomas in these studies with similar people who didn’t, they found that the glioma group was more likely to develop gliomas. T. gondii antibodies. Generally, the presence of T. gondii was associated with a more than two-fold increased risk of glioma. In people with the highest levels of a certain type of antibody against it T. gondiithe associated risk was more than three times as great. About 350 people with a glioma, including those over 70 and under 40, were studied, with similar associated risks seen in both age groups.
Other studies have found it a similar link between T. gondii and brain cancer. However, according to the authors, their evidence is the first evidence of what is known as prospective research, namely when people are observed before developing the condition under study. That’s important, because scientists can clearly know thing A – in this case T. gondii infection – happens before thing B – brain cancer. This alone cannot prove that T. gondii helps cause brain cancer, but it’s evidence that the connection is more likely to be real.
The findings suggest that individuals with higher exposure to the T. gondii parasite are more likely to develop glioma, ”said study author Anna Coghill, a researcher at the Moffitt Cancer Center, in a statement released by the American Cancer Society. “However, it should be noted that the absolute risk of being diagnosed with a glioma remains low, and these findings need to be replicated in a larger and more diverse group of individuals.”
There are about 24,000 new cases of brain cancer estimated occurs annually in the US, accounting for about 1% of all cancers. Meanwhile, it is thought that 11% of Americans over the age of six T. gondii, so more than 30 million people. That means that even if this connection is real, the chances of brain cancer are due to chronic T. gondii infection is very low on an individual level. Likewise, not everyone who develops glioma will get it T. gondii, and there are people with T. gondii who would have gotten brain cancer, even if the infection never happened – the cancer risk is complicated like that.
Still, this is the latest piece of research to suggest that hidden infections in the body and brain can affect our health long after they first arrive.