Health

The bont-legged tick under surveillance

Science at work 19 June 2020

Since 2015, CIRAD has been studying the tick Hyalomma marginatum , which has been regularly observed along the Mediterranean coast in France. The exact origin of this species, which has been present in Corsica for several decades but has only recently arrived in mainland France, is still unknown. Unlike the species Ixodes ricinus, this tick is not a vector of the bacteria that causes Lyme disease. But it can transmit Crimean-Congo haemorrhagic fever, a virus that has not yet been detected in France.

Hyalomma marginatum, la tique à pattes rayées, affectionne la zone méditerranéenne et s’y développe de mars à août. © F. Stachurski, Cirad

The adult ticks measure up to 8 mm in length: they are slightly larger than others, “but several of the tick species found in our Mediterranean regions can nevertheless reach the same size ”, according to Laurence Vial and Frédéric Stachurski, veterinarians and researchers in parasitology at CIRAD. “It is therefore an exaggeration to call them giant ticks ”. However, “they are known as bont-legged ticks, and their striped legs make them easily recognisable ”.

Currently observed in garrigue or dry hilly areas along the Mediterranean coast in several French departments (Pyrénées-Orientales, Aude, Hérault, Gard, Bouches-du-Rhône, Var, and in southern Ardèche), this tick seems to have been progressing for the last five years in these Mediterranean regions to which it is suited. “We are studying its installation, its ecological niche, and its tolerance to different temperatures, humidity levels and rainfall regimes, to understand the factors that explain its expansion ”, say the researchers. “For this reason, we are interested in any reports by farmers or individuals recognising this tick”.

These ticks attach to certain animals, and accidentally to humans, when they are immobile, and far more rarely when they are moving. They are found in fields or garrigue from March to August. “Unlike other tick species that wait for hosts on blades of grass, these ticks move towards the host, which they identify through vibrations in the ground or breathing ”. They can move several metres, but once attached to an animal, they can then be transported over long distances and thereby extend their distribution area.

A tick that attaches to certain animals, but is not harmful to them

Adult ticks attach to horses, cattle, sheep, goats, wild boar and deer, without doing them any harm except for small wounds if the infestation is too heavy. After engorging on the blood of their host, female ticks drop to the ground and lay eggs in the environment. From early July to late September, the larvae from the eggs attach to small mammals (especially hares and rabbits) and birds (especially blackbirds but also thrushes, robins, finches, etc.). Once engorged, the larvae moult on the host into nymphs that then engorge again, before dropping off three weeks after the larvae attached.

What dangers do Hyalomma marginatum ticks pose to humans?
This tick is not dangerous in itself: its bite can cause an irritation that last several days, if the tick is not removed quickly. However, ticks may carry an infectious agent that can occasionally be transmitted through bites. But not all ticks carry these infectious agents and not all bites are infectious.

Hyalomma marginatum can thus transmit the Crimean-Congo haemorrhagic fever virus to people. Although positive serological results have recently been reported in cattle in Corsica, this virus has not yet been detected in mainland France. However, it is very widespread in Africa, Asia, the Middle East and Turkey, where it recently caused an epidemic. In Europe, it is present in the Crimea, Romania and the Balkans, from Greece to Albania, and it has recently appeared in Spain.

What should you do if you have a tick?
After a walk in the countryside, check your whole body to find any ticks. If one of these ticks has attached itself, or a tick of a different species, it should be removed as quickly as possible before it begins to engorge. It is best to use a tick removal tool, or a tick can be removed by hand, taking care to pinch it at the base between the thumb and the index finger.

Report any tick bites on citique.fr (a participatory research programme in which citizens can contribute to research on ticks and the diseases they transmit), or on the associated smartphone application .