Tick-borne diseases spread across Europe due to global warming

Laure Bournet, project leader of TIQUoJARDIN, in front of a microscope with a female tick in the laboratory of the National Agency for Food Safety, Environment and Occupational Health in Malzeville (Meurthe et Moselle), June 3, 2022.

From the north to the south of France, the tick is everywhere. For several years now, the metropolitan area has been divided by four species capable of carrying various bacteria, viruses and other parasites harmful to humans. If Lyme borreliosis caused by bacteria borrelia burgdorferi, is the best known of these tick-borne diseases, new threats have been noted by health authorities in recent years, including tick-borne encephalitis and Crimean-Congo fever.

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In the northern hemisphere, ticks are major disease vectors for both human health and veterinary medicine. According to Public Health France (SPF), the number of cases of Lyme borreliosis is increasing significantly: the incidence rate has risen from about 40 cases per 100,000 inhabitants in 2009 to 90 cases per 100,000 inhabitants in 2020, with fluctuations depending on the year. Since 2016, there has been a fluctuation between 47,000 and 70,000 new cases per year.

Bacterial infestation can be rapidly reversed with antibiotic treatment when diagnosed shortly after the bite, after identifying and removing the tick, or when erythema migrans, an inflammatory red spot around the bite, appears. But in case of late diagnosis, the disease can progress with the appearance of the first symptoms, such as headache, fatigue and pain in the muscles or joints, and then dissemination in many organs. “Anyone can get Lyme disease and there is no protective immunity, which means you can get it several times in a lifetime”explains Nathalie Boulanger, medical entomologist who leads the research group on tick-borne diseases at the University of Strasbourg.

The species responsible for the transmission of this disease areixod caster, are present throughout Europe up to the Arctic Circle, as shown on maps compiled by the European Center for Disease Prevention and Control. The same species is the vector of about twenty other pathogens, one of which is of particular concern to the authorities: tick-borne encephalitis virus. Still rare, according to a recent SPF report, there have been 71 cases in France since 2021.

“Distribution in full evolution”

This disease with low mortality but significant consequences initially presents with fever and pain, but can later lead to serious infections of the nervous system such as encephalitis or meningitis. In France, a country less affected than Austria or Germany, the two most famous outbreaks were in Alsace and Haute-Savoie. But in 2020, an outbreak was identified in Aina linked to eating raw milk cheeses, with infected goats shedding the virus into their milk. ‘Virus circulation is wider than expected’warns Alexandra Miles, an epidemiologist at the SPF infectious disease division, citing cases in some departments that have not yet been identified as at risk, such as Ardèche and Cantal. “And most cases were not considered cured after hospitalization”she adds. With careful observation, the disease was reported within two years.

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