Bien que toute petite, la tique si elle est infectée par une bactérie de la famille des spirochètes peut-être dangereuse et déclenchée la maladie de Lyme sur l

MAP. Lyme disease: these are the areas of France where ticks proliferate the most

Although very small, the tick, if infected by bacteria from the spirochete family, can be dangerous and trigger Lyme disease in humans. (©Sebastian Kaulitzki? (©Chalabala/Adobestock)

According to the latest available data, probably more than 60,000 people contract the disease each year. Lyme borreliosis Where Lyme’s desease.

Generally, hospitalizations for this pathology linked to a tick bite between June and October and children from 5 to 9 years old and adults from 70 to 79 years old would be the most affected.

Although the incidence rate tends to increase, and if not diagnosed in time, this disease can cause lasting joint pain or even partial paralysis of the extremities, the authorities have decided to distribute a map, and reiterate advice, common sense.

These marked areas in France

A team made up of researchers from the National Research Institute for Agriculture, Food and the Environment (Inrae), the National Institute for Higher Education and Research VetAgro Sup (merger of the National Veterinary School of Lyon, the National School of Engineering Agricultural Institute of Clermont and the National School of Veterinary Services), ANSES (National Agency for Food, Environmental and Occupational Health Safety) and CIRAD (Center for International Cooperation in Agricultural Research for Development) have just published a map showing the areas where ticks “Ixodes ricinus” are found most frequently.

What we see? The eastern and central regions (Alsace, Lorraine, Limousin in particular) have high annual incidence rates (more than 100 cases per 100,000 inhabitants), the western and south-eastern Mediterranean regions have lower annual incidence rates (less than 50 per 100,000 population) .

As for the Mediterranean and high mountain regions, they are the least favorable to the proliferation of ticks, and appear in green on the map.

Lyme borreliosis or Lyme disease is an infectious disease caused by a bacterium of the Borrelia burgdorferi sensu lato complex that is transmitted to humans through the bite of infected ticks.
Areas where ticks are most numerous (©INRAE)

In deciduous forests, undergrowth, pastures and meadows…

If the disease is present throughout the metropolitan territory, there are significant geographical disparities. These “Ixodes ricinus” ticks live in deciduous forests, undergrowth, pastures/meadows, they are rare in coniferous forests.

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They can also be found in peri-urban wooded areas and in urban parks and private gardens. The “Ixodes ricinus” tick has never been detected in the overseas departments and regions, due to a climate not suitable for its development, but care must be taken throughout the year in case of temperate and humid climate as in Brittany.

Lyme borreliosis, or Lyme disease, what is it?

Lyme borreliosis or Lyme disease is an infectious disease caused by a bacterium of the Borrelia burgdorferi sensu lato complex transmitted to humans by the bite of infected ticks, explains Public Health France. Lyme borreliosis is the most common tick-borne disease in France.

How do these ticks behave?

Ticks are mites that take “their blood meal” from animals, and humans are accidental hosts, underlines Public Health France. The search for a host for its blood meal is carried out when the environmental conditions are optimal (humidity, temperature).

The Ixodes ricinus tick’s developmental cycle takes place in several stages, and the length of this cycle varies from two to six years, the researchers determined. From the egg a larva is born that transforms into a nymph (2 mm) and then an adult (3-4 mm). A blood meal in a host is required for egg laying by the adult female tick and at every stage of its development.

The “Ixodes ricinus” tick then becomes infected by feeding on the blood of hosts contaminated with the bacteria “Borrelia burgdorferi sensu lato”.

The “blood meal” lasts from three to seven days depending on the stage. At the end of the “meal”, the tick detaches itself from its host and falls into the vegetation.

Public health France

The main reservoir hosts of Borrelia burgdorferi sensu lato? They are small wild mammals (voles, field mice, squirrels, etc.). Certain species of birds or reptiles are also reservoirs. Large mammals such as deer are hosts for adult ticks, but incompetent reservoirs of Borrelia burgdorferi, that is, unable to transmit the bacteria to an uninfected tick.

The “blood meal” lasts from three to seven days depending on the stage. At the end of the “meal”, the tick detaches itself from its host and falls into the vegetation. It needs a minimum of humidity to survive (80%) and can wait several months to move on to the next stage of the cycle or lay its eggs if it is a female tick.

How is Lyme disease spread to humans?

Borrelia burgdorferi is transmitted to humans through the bite of an infected tick of the Ixodes ricinus complex. During the “blood meal” that follows the bite, bacteria from the tick’s gut pass into its salivary glands.

Salivary transmission depends on contact time and tick infestation rate.

In US studies, the risk of transmission appears low for attachment durations of less than 72 hours. In Europe, experimental and clinical data have shown that this period would be shorter with a higher risk after 24 hours of connection, details Public Health France.

Humans can be bitten by a tick at any stage of development (larvae, nymphs, adults), but nymphs appear to be responsible for the majority of transmissions. Lyme borreliosis is not spread from person to person, or by direct contact with animals, or through food, or by the bite of other insects.

What are the symptoms of Lyme disease?

How to know if you are sick? Most commonly, you will experience a skin rash “called erythema migrans”. The symptoms of Lyme borreliosis depend on the stage of the disease. The first occurs 3 to 30 days after the tick bite. It is characterized by this typical skin manifestation. It is “an erythematous spot, at the site of the tick bite, painless and with annular and centrifugal growth,” details Public Health France.

Erythema migrans is the most common manifestation (60 to 90% of cases) and the most suggestive of Lyme borreliosis.

Neurological manifestations are also possible (facial paralysis, isolated meningitis, acute myelitis). And more rarely joint manifestations (arthritis with the notion of effusion of a large joint such as the knee), skin (borrelian lymphocytoma), cardiac or ophthalmological. Symptoms that can occur several months or even years after the tick bite. Therefore, it is advisable to perform a serological test to look for specific antibodies against Borrelia burgdorferi sensu lato.

How to treat Lyme disease?

To overcome Lyme borreliosis, antibiotic treatment is sometimes necessary. In the early localized stage, antibiotic therapy allows healing of erythema migrans but also prevents disease progression.

There is currently no vaccine available against Lyme borreliosis or against tick bites. However, there is a vaccine available against tick-borne encephalitis (but it does not protect against other tick-borne infections such as Lyme Borreliosis).

How to protect yourself from ticks?

It is advisable to walk along well marked trails, without dense vegetation and tall grass, wearing clothing that covers, possibly impregnated with repellents. Wearing light colored clothing also makes it easier to spot ticks that have not yet attached to the skin.

If you think you have found a tick, a careful examination (because the tick, in the nymph stage, is only 1 to 3 mm long) of the body after exposure to the risk of bites is necessary. Special attention should be paid to “skin folds, the back of the knees, the armpits, the genital areas, the navel, and, particularly in young children, the scalp, the neck, the back of the ears”, list the authorities. .

It may be helpful to re-inspect the next day because the tick, partially engorged with blood, will be more visible.

Another important tip is to remove the tick as quickly as possible to avoid Borrelia transmission because the risk of transmission increases with attachment time. Use a tick hook (available at pharmacies) if possible, otherwise fine tweezers or tweezers (do not pull the tick with your fingers) and disinfect the bite site after tick removal.

Then monitor the bite area for four weeks. In case of appearance of migratory erythema (red and round plaque) or general signs (fever, malaise, body aches) you should consult your doctor. Several infections can be transmitted by ticks in France in addition to Lyme Borreliosis, but they are much rarer.

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