Carried by migratory birds, ticks’ survival is improving as the climate warms – Technologist

Ticks know virtually no borders. So said a study published Monday, November 18, in the journal Frontiers in Cellular and Infection Microbiology. These blood-feeding mites have a prime means of transport: migratory birds. Clinging to their host, they travel thousands of kilometers, well beyond their usual distribution zones. With global warming, they are also surviving longer at their destination, as are the pathogens they carry.

To study this phenomenon, American researchers set up bird traps along the Gulf Coast. Once captured, the birds were identified and examined for ticks. The scientists then mapped the geographical distribution of the migrants to understand where they might have contracted these parasites.

Lyme borreliosis, the most widespread disease

The results showed that ticks could be transported over distances of up to 5,000 km, explained Shahid Karim, from the University of Southern Mississippi and lead author of the study. Karim said that “this demonstrates that ticks are now reaching areas where they would never have been able to establish themselves before. Rising temperatures linked to climate change are providing them with conditions conducive to their establishment and spread.”

This is a worrying situation, given that ticks are excellent vectors of pathogens responsible for animal and human diseases.

The most widespread tick-borne disease is Lyme borreliosis, caused by the bacterium Borrelia burgdorferi sensu lato, transmitted to humans through the bites of infected hard ticks of the genus Ixodes. According to the study, in the United States, over 95% of vector-borne diseases are linked to these parasites. “Not only could these ticks bring new pathogens, but if they manage to establish themselves in the US, they could become additional vectors of pathogens already present in this country and transmit them to wildlife and humans,” explained Karim.

In all, the researchers collected 421 ticks from 164 birds, a “not insignificant” number according to arthropod researcher Sarah Bonnet from the Pasteur Institute: “Four hundred is enough for a population to establish itself. A female tick can lay thousands of eggs at a time. So, if all the conditions are right, a single fertilized tick could enable the establishment of a new species.”

This phenomenon is not confined to the US but has also been observed in Europe in recent years. In October 2023, and for the first time in France, the Crimean-Congo hemorrhagic fever virus (CCHF) was detected in ticks of the species Hyalomma marginatum, native to Africa and Asia.

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