Another danger of toxoplasmosis
The "zombie parasite" of cats can cause cancer and brain diseases in humans
Human infection with toxoplasma – a cat parasite that turns mice into "zombies" – was associated with an increased likelihood of developing epilepsy, Alzheimer's and Parkinson's diseases and some types of brain cancer, according to an article published in the journal Scientific Reports (Toxoplasma Modulates Signature Pathways of Human Epilepsy, Neurodegeneration & Cancer).
"We assume that the development of these diseases affects many different factors. One of them is the parasite itself and the genes that it activates in the infected brain, protecting itself from the attention of the immune system. Other risk factors may include pregnancy, stress, other infections and poor microflora. If some of these factors coincide, then one of the brain diseases may occur," says Rima McLeod from the University of Chicago (USA).
Toxoplasma gondii is an intracellular parasite that usually lives in the intestines of domestic cats. To date, according to the American CDC, more than 60 million US residents have been infected with it. The widespread prevalence of this pathogen among pets and their owners forced scientists to pay attention to it.
It turned out that toxoplasma is able to change the behavior of the host, causing irreversible changes in the brain. It makes mice and chimpanzees fearless at the sight and smell of cats and leopards, and humans prone to suicide and irrational acts, as well as unexplained fits of rage. In addition, in a pregnant woman, toxoplasma can cause serious defects in the development of the fetus and lead to miscarriage.
MacLeod and her colleagues found out that getting this parasite, which was previously considered relatively harmless, into the human brain can lead to the development of very serious problems. To do this, scientists studied what changes in the brain are caused by Toxoplasma gondii, and analyzed how often the possible consequences of these changes occur among healthy and infected people.
They were helped in this by the fact that the University of Chicago has been monitoring the lives of about three hundred families whose members were infected with toxoplasmosis for almost forty years. This allowed scientists to understand how the parasite can affect the development of health problems associated with brain function.
As these observations have shown, toxoplasma, penetrating into the brain, changes the work of several dozen genes, suppressing some of them and enhancing the work of other DNA sites. Almost all of these genes either control the work of the innate immune system, or conduct various processes associated with the growth of stem cells and new tissues. The feline parasite suppresses the work of the first group of genes, which helps it survive, and stimulates the work of the second set, providing itself with food.
Both do not pass without a trace for an infected person, since the weakening of the immune system makes him more predisposed to the development of cancer and neurodegenerative diseases associated with malfunctions of the immune system. Excessively strong changes in the work of other genes can change how many different signaling molecules the brain produces, as a result of which epilepsy, schizophrenia and other mental disorders can develop.
What is most interesting, scientists have found traces of the same changes in the work of human olfactory receptors that make monkeys and mice not afraid of the smell of cats. Biologists do not yet know how this affects human behavior, but they plan to find out during further experiments with toxoplasma.
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14.09.2017