Toxoplasmosis: Why does the cat parasite spread so well in humans? – Insurance for Pets

PARIS, Oct. 31 (Benin News) –

A study by researchers from the University of Stockholm (Sweden) discovered how the Toxoplasma parasite spreads in the body, for example to the brain, to the point of being carried by a large part of the world’s population. The researchers found that the parasite infects immune cells and hijacks their identity, as they report in the journal Cell Host & Microbe.

To fight infection, the various functions of the body’s immune cells are tightly regulated. Scientists have long wondered how Toxoplasma manages to infect so many people and animal species and spread so efficiently.

“We have now discovered a protein that the parasite uses to reprogram the immune system,” explains Arne ten Hoeve, a researcher at the Department of Molecular Biosciences at the Wenner-Gren Institute at Stockholm University.

The study shows that the parasite injects the protein into the nucleus of the immune cell and thus changes the identity of the cell. The parasite tricks the immune cell into thinking it is another type of cell. This alters the gene expression and behavior of the immune cell. Toxoplasma causes infected cells, which normally should not move around the body, to move very quickly and the parasite thus spreads to different organs.

This phenomenon has been described as Toxoplasma’s transformation of immune cells into traveling Trojan horses or « zombies » that spread the parasite. The recently published study offers a molecular explanation for the phenomenon and also shows that the parasite is much more selective in its spread than previously thought.

“It is surprising that the parasite manages to hijack the identity of immune cells in such a clever way. We believe these results may explain why Toxoplasma spreads so efficiently through the body when it infects humans and animals,” says Professor Antonio Barragan, who led the study, conducted in collaboration with researchers from France and the United States.

Toxoplasmosis is probably the most common parasitic infection in humans worldwide. Toxoplasma also infects many animal species (zoonoses), including our pets. The WHO has estimated that at least 30% of the world’s human population carries the parasite. Studies indicate that 15-20% of the Swedish population carry the parasite (the vast majority unknowingly). The incidence is higher in other European countries.

Felines, and not just domestic cats, occupy a special place in the life cycle of Toxoplasma: it is only in the intestine of the cat that sexual reproduction takes place. In other hosts, for example humans, dogs or birds, reproduction takes place by division of the parasite.

It is transmitted through food and contact with cats. In nature, the parasite preferentially spreads from rodents to cats, from cats to rodents, and so on. The parasites are « dormant » in the rodent’s brain and when the cat eats the mouse, they multiply in the cat’s intestine and pass out through the stool. The parasite is found in the vegetation and when the rodent eats the vegetation, it becomes infected. Humans become infected by eating meat or coming into contact with cats, especially through their excrement.

This parasite is the cause of toxoplasmosis. When a person is first infected, they experience mild cold or flu symptoms. After the first phase of infection, the parasite enters a « dormant » phase in the brain and begins a silent, chronic infection that can last for decades or even a lifetime. The chronic infection usually causes no symptoms in healthy people. However, Toxoplasma can cause a life-threatening brain infection (encephalitis) in people with weakened immune systems (HIV, organ transplant recipients, after chemotherapy) and can be dangerous to the fetus during pregnancy. Eye infections can occur in otherwise healthy people.