They are mainly known for the transmission of Lyme disease. Ticks, feeding on the blood of various animals, can transmit pathogens to humans. These mites can carry many bacteria and viruses. New bacteria transmitted by ticks have just been described in a study published in the journal Nature Communications. Previously unknown, they can be transmitted to humans and endanger their health.
“ There are more than 900 species of ticks in the world »
“ There are more than 900 species of ticks in the world but only a few dozen bite humans and even fewer bite them very regularly.“, explains Olivier Duron, CNRS researcher specializing in the ecology of infectious diseases and lead author of the study. To track ticks, research has long studied the host animals on which they feed.
“We have studied dogs, cows, chickens and pigs a lot, but wildlife is little studied to better understand ticks”, he adds. In the northern hemisphere, the animal is closely followed by the domestic animals around us. “ But ticks specializing in reptiles, seabirds, arboreal animals such as monkeys and even rhinoceroses are neglected.. »
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10% positive samples
To better observe the species in all its diversity, the team went to Guyana, where they collected ticks from more than 20 different species of animals, from anteaters to sloths, thanks to the collaboration of wildlife specialists. on the spot. But many ticks also wait in nature to find an interesting host who might pass by. “ To harvest them, we advance through the vegetation with large pieces of white sheets impregnated with our body odor and our perspiration. Clinging to their leaves, ticks detect odor and movement then drop into the sheet,” describes Olivier Duron. All that remains is to collect them.
Finally, a collaboration with thePasteur Institute of Guyana made it possible to recover animal organs as well as human blood samples to analyze for potential microbes. These blood samples from the Cayenne hospital come from a population of Brazilian gold miners. “ They filter water, deforest and live in the forest. However, their water points are larval breeding grounds for mosquitoes where malaria and yellow fever circulate.“, explains the researcher.
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To ensure an approach “Without A Priori” In the research, the team avoided using overly specialized molecular tools. “ In medical laboratories, there are very effective but very specific tests. They recognize very well the illnesses that we know about but miss those that we don’t know about.”, specifies Olivier Duron. By passing their samples through high-throughput sequencing, the DNA revealed the presence of numerous bacteria.
“But 99.9% of them did not interest us because they are environmental bacteria or living in symbiosis with the tick. » Looking more specifically for tick diseases, 10% samples came back positive. A rate " huge ", which surprised the researchers. These bacteria are part of the branches Anaplasma And Ehrlichia, known to affect either red blood cells or white blood cells depending on the species. By going a step further in DNA sequencing, “ we were surprised to find previously unknown species”, announces the researcher.
Three new bacteria identified
These new bacteria, difficult to sequence, required a lot of bioinformatics work. A real technical challenge which made it possible to pinpoint three new bacteria. One from a sloth, the second from a tick and the third from a human. That of a gold prospector falls ill. First taken care of in a dispensary, he was hospitalized in Cayenne for three weeks where, despite a battery of tests, the hospital was unable to find out what he was suffering from. “ Fortunately, a course of antibiotics treated him within 15 days, before he returned to Brazil.“, says Olivier Duron.
Tick diseases are not the same in the northern hemisphere as in the southern hemisphere. It is also not the same species of ticks that evolve there. But the zoonoses, infectious diseases that pass from animals to humans, can occur anywhere. Whether tourists, foresters or gold prospectors, everyone is exposed to these new bacteria for which the risk of transmission is proven. “ The more we go into these habitats, the more it will create new opportunities.. » The researcher emphasizes the immensity of the transmissible pathogens that remain to be discovered. Guyana, where the work was carried out, only represents 1% of the surface of the Amazon forest.
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