Toxoplasmosis is a very strange disease. For ordinary mortals, it remains a mild infection, often even invisible, causing at worst a mild fever and a few pimples. Benign and very common as it is thought to affect 30% of humanity. But if your immune system turns out to be severely deficient, the pathogen can be fatal. The ravages wrought among AIDS patients are a reminder of this. The fetus, whose immunity is still faltering, is the other weak point of our species. If it infects the mother, the parasite can seriously affect the proper development of the future baby.
Pregnant women all know it: the domestic cat is the primary carrier of the parasite. Above all, do not change the litter if you are not already immunized by a previous infection, hammer the gynecologists. In fact, the connection between Toxoplasma gondii – the full name of the pathogen, discovered in 1908 in a small Tunisian rodent, the gondii – and the cat goes far beyond the risk it poses to us humans. In an article published in Nature communicationreveals a team from the University of Limoges, which houses the National Reference Center for strains of the parasite, that its evolution and spread over the five continents is closely linked to the domestication of the cat.
This observation is not entirely a surprise, as Felidae have a special place in the Toxoplasma cycle. If this single-celled protozoan can infect almost all warm-blooded animal species (mammals, birds, etc.) and survive on plants, this whole little world is only a stepping stone to the parasite’s final goal: felines. In all the so-called intermediate hosts, Toxoplasma must be content with asexual reproduction. But in the body of the cat and its forty cousins, it drives a sexual reproduction.
No one knows if the protozoan finds personal satisfaction in it. But the species has a real advantage from it. “It is in felines that diversification can take place, the meeting of different strains, their recombination”, explains Aurélien Mercier, lecturer at the Faculty of Pharmacy in Limoges and coordinator of the study. To achieve this supreme happiness, Toxoplasma goes so far as to manipulate its intermediate hosts: infected mice stop running away from cats, monkeys fall in love with leopards, hyenas with lions… with the result you can imagine.
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