Trojan horses or walking zombies – we’re talking about Toxoplasma gondii. Hardly any other parasite is so widespread worldwide, one third of humanity is infected. Now his secret has been unlocked.
There Parasite Toxoplasma gondii is at about a third of the world’s population to find – the majority of people are infected without even knowing it. In Germany, people become infected mainly by eating meat. The serum prevalence increases between the ages of 20 and 80 Toxoplasma IgG antibodies linearly at about 1% per year from 20% to 77%.
How humans get infected
The main host of the pathogen is the cat, which develops through oral ingestion of the oocysts infected. The unsporulated Oocysts are then passed in the feces – they are not yet infectious at this point. Under favorable conditions, they sporulate in the environment within a few days. At this stage, the oocysts are both for intermediate hostssuch as farm animals or humans, as well as for the cat as Endwirt infectious. Cats occupy a special position in the life cycle of Toxoplasma: sexual reproduction only takes place in the cat’s intestine. In other hosts, e.g. B. humans, dogs or birds, the propagation takes place by division.
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Transmission to humans then usually occurs through food contaminated with oocysts (raw pork or lamb, unwashed fruit and vegetables) or contact with cat faeces. The infection is harmless to healthy adults. An initial infection usually runs its course asymptomatic or under training nonspecific general symptoms How fatigue, Headache or lighter Fever. After an oral infection spreads T. gondii from the gut to peripheral organs such as the central nervous system. Rarely does it happen Lymphadenopathy (Piringer-Lymphadenitis), maculopapular exanthema, Chorioretinitis, Myalgien or diarrhea. Recurring eye diseases can also occur in immunocompetent people. Through residual tissue cysts, infected people develop lifelong cysts immunity.
In immunocompromised people (eg HIV infection), however, the initial infection or reactivation of oocysts remaining in the body can lead to serious progression with organ damage (Myocarditis, encephalitis, Hepatitis) and Pneumonia come. In the case of an initial infection during pregnancy, it can diaplacental to the Infection of the Embryos come. The child’s probability of infection increases with the age of the pregnancy, while the severity of the infection decreases.
Reprogram host cell
Scientists have long wondered how Toxoplasma manages to infect so many people and animal species and spread so efficiently. A group of researchers from Sweden and France has now been able to show how the parasite spreads so successfully in the body of its hosts. T. gondii not only infects immune cells, but subsequently takes control of the cell. The Study was in the journal Cell Host & Microbe published.
“We discovered a protein that the parasite uses to reprogram the immune system,” said Arne ten Hoeve, researcher at the Department of Molecular Biosciences, at Stockholm University and first author of the study. His group was able to show that the parasite injects the protein GRA28 into the cell nucleus of the immune cell, thereby changing its gene expression and behavior.
To be precise: the infection causes T. gondii at macrophageswhich do not normally migrate to other organs, induces the expression of transcription factors that are typically associated with migratory dendritic cells are associated. The researchers describe this phenomenon as Toxoplasma turning the macrophages into something like Trojan horses or wandering zombies, which then spread the parasite throughout the organism. The study that has now been published provides a molecular explanation for this phenomenon and also shows that the parasite spreads in a much more targeted manner than previously thought.
The tricks of the pathogens
Ten Hoeve and his team see parallels to other pathogens such as Mycobacterium tuberculosiswhich manipulates alveolar macrophages to rapidly colonize the lung interstitium or den Leishmanienwhich influence transcription and epigenetic regulation in macrophages and thus modulate the host immune response.
“It is amazing that the parasite is able to hijack the identity of the immune cells in such a clever way. We believe the results may explain why Toxoplasma spreads so efficiently in the body when infecting humans and animals,” says Prof Antonio Barragan, leader of the study, which was carried out in collaboration with researchers from France and the US.
You can find the study here and deposited in the text.
Image source: Ahmad Zayan, unsplash