Understanding and combating tick-borne pathogens

What diseases are linked to ticks?

Tick-borne diseases can be:

• bacterial (e.g. Lyme disease, rickettsiosis, tularaemia, bartonellosis);
• viral (e.g. tick-borne encephalitis, tick-borne fevers and haemorrhagic fevers such as Crimean-Congo haemorrhagic fever, sheep wolf-ill);
• parasitic (e.g. canine piroplasmosis, bovine babesiosis, anaplasmosis).

The main human tick-borne disease in France is Lyme disease, caused by Ixodes ricinus.

ANSES studies both ticks and the pathogens they transmit, in order to identify and characterise them and combat their harmful effects.

Find out more about tick vectors and the diseases they transmit.

How do tick vectors transmit the pathogens that cause disease?

Ticks feed on the blood of the animals or humans to which they attach themselves. They can then become infected by picking up pathogens from infected hosts. They then multiply and retransmit these pathogens to other hosts when they take another blood meal. Ticks are therefore considered "vectors" of pathogens responsible for animal and human diseases. Transmission occurs mainly via their saliva.

Ticks are very good vectors because:

• many species take very large blood meals (some females are capable of absorbing up to 100 times their weight in blood) and take a long time to do so (from around 3 to 12 days, depending on the tick’s stage of development). They therefore have a greater chance of absorbing and transmitting a pathogen than other species. For example, it is estimated that the female Ixodes ricinus tick absorbs around 1 ml of blood;
• attached to their host, ticks can travel great distances (widespread dissemination);
• due to their very long lifespan (several years), the pathogens they carry are maintained in the wild for long periods;
• many species of tick feed on several different types of host which may be carriers of a variety of pathogens, thus enabling micro-organisms to circulate widely among animal species. For example, Ixodes ricinus nymphs can feed on the blood of birds (passerines) or small mammals (rodents), and in adult form on larger animals (deer, chamois, etc.) or humans;
• they reproduce in very large numbers (from around a hundred eggs to several thousand, depending on the species);
• their bite is painless due to substances in their saliva.

Lyme disease, the main tick-related human disease in the northern hemisphere

In France, the main human disease associated with ticks is Lyme disease. It is caused by a bacterium belonging to the Borrelia burgdorferi sensu lato group, which includes at least 5 species that are pathogenic to humans, and is present in France.

A few days after a tick bite, in the event of infection, an erythema migrans (characteristic red halo on the skin) appears around the site of the bite and spreads in a circular fashion. At this stage, treatment with an antibiotic can stop the disease. Without treatment, the disease can cause skin, muscle, neurological and joint disorders that can be highly disabling. Antibiotic treatment is available and is effective if administered quickly, hence the importance of a rapid diagnosis after a tick bite.

Crimean-Congo haemorrhagic fever: possible emergence in France

The Hyalomma marginatum tick, which has been present in Corsica for several years, could spread to France as a result of climate change. This tick, which thrives in dry climates and warm weather, can transmit Crimean-Congo haemorrhagic fever (CCHF). In humans, this disease is generally limited to a flu-like illness with digestive problems. In some cases, however, it can worsen and lead to a haemorrhagic syndrome, with a fatality rate of up to 30% in some countries. To date, no indigenous cases have been detected in humans in France, but cases have been reported in Spain every year since 2016.

Find out more about possible emergence of Crimean-Congo haemorrhagic fever in France.

Tick-borne encephalitis, a virus that can cause neurological disorders

Tick-borne encephalitis virus is mainly transmitted to humans by bites of infected ticks of the genus Ixodes. Cases can also occur following consumption of unpasteurised dairy products, as ruminants can be infected by a tick bite and then shed the virus in their milk for several days.

In humans, symptoms occur in 20 to 40% of infections. They are mainly flu-like (fever, fatigue, headaches, aches and pains) and digestive symptoms. A third of clinical cases may progress to a more severe form, with the appearance of neurological signs such as meningitis or meningoencephalitis, leading to hospitalisation. This disease can cause serious complications, with neurological sequelae such as paralysis or behavioural or memory problems that can persist for several years.

How can I protect myself from tick bites?

To protect yourself from tick bites when walking in the forest, scrubland or maquis, or when spending time in your garden:

• wear closed shoes and clothing that covers the body; light colours will help you more easily identify any ticks on the surface of the fabric
• avoid walking through long grass, bushes and low branches and keep to signposted paths instead
• inspect your body when returning from walks
• if you are bitten, remove the attached ticks immediately using a tick remover, fine tweezers or your fingernails (never use ether or any other product) and disinfect the wound
• monitor the bite area for several days and see your doctor if you develop any symptoms
• use repellents, opting for those with marketing authorisation and comply with their conditions of use (all this information is given on the product's label, packaging and/or leaflet).

After a tick bite, consult your doctor immediately if any symptoms appear (fever, tiredness, redness).

What is ANSES doing about ticks?

Several ANSES laboratories are developing research on ticks

The Animal Health Laboratory in Maisons-Alfort studies ticks and tick-borne pathogens. To this end, tick collections are regularly organised in various regions of France and the pathogens found in these ticks are identified using high-throughput techniques. The laboratory is also developing innovative methods to improve epidemiological surveillance of these pathogens. The ability of ticks to transmit identified pathogens is also the subject of research activities, as is the study of interactions between ticks, tick microbiota and pathogens. Finally, the laboratory is developing innovative tick control tools, such as anti-tick microbiota vaccines.

The Laboratory for Rabies and Wildlife studies the eco-epidemiology of tick-borne infectious agents. This work aims to improve understanding of their epidemiological cycles in wildlife and host-vector-pathogen interactions. Another objective is to understand the distribution of ticks and the infectious agents they carry, as well as the factors influencing these distributions. Lastly, the Laboratory examines situations where humans are at risk of exposure to tick bites as well as the infectious agents involved. In particular, the Laboratory's work includes the study of tick-borne encephalitis virus.

Other ANSES laboratories study diseases transmitted by ticks on a more ad hoc basis, such as the Ploufragan-Plouzané-Niort Laboratory, which took part in research on the role of ticks in the transmission of African swine fever. These studies enable ANSES to gain a better understanding of the pathogens transmitted by ticks, and thus to better combat infectious diseases.

This research theme, at the interface between animal and human health, fits perfectly with the "One Health" concept being implemented by the international health authorities.

Find out more about the 'Ticks and tick-borne diseases' group in which ANSES researchers are taking part. (in French)

Assessing risks

In addition, since 2018, ANSES has been carrying out specific scientific assessments on vectors and vector control.

It aims to support the public authorities in order to improve prevention and control of the risks associated with the transmission of pathogens by vectors, including ticks.

Assessment of biocidal products

ANSES is also responsible for assessing the risks to humans, animals and the environment, and the efficacy of active substances and biocidal products.

In Europe, 12 active substances likely to be effective against ticks have been approved or are currently being examined for approval.

Due to the gradual implementation of the Biocide Regulation, the vast majority of products claiming repellent efficacy against ticks are not yet subject to marketing authorisation (MA) and have therefore not yet been assessed.

Products with marketing authorisation have undergone a full assessment, and the marketing authorisation includes instructions for use (including doses and duration of protection) guaranteeing, under the recommended conditions of use, effective protection against ticks and the absence of harmful effects on human health and the environment.

The list of products with marketing authorisation, whose efficacy has therefore been verified, is likely to evolve as the dossiers are examined and depending on the approval of active substances at European level.

To date, only products containing exclusively DEET as an active substance have been evaluated, and the evaluation of IR3535-based products is currently being finalised.

For these products, the conditions of use guaranteeing effective protection against ticks and the absence of unacceptable risks to human health and the environment are specified in the marketing authorisations, and appear on the label, packaging and/or product leaflet.

Consult the AST note (PDF in French) on repellents claiming to be an effective repellent against ticks.

Want to find out more about ticks and everything else that bites?

Discover our futuristic podcast Zootopique (in French) and listen to the episode on ticks and everything that bites, to find out how today's science is anticipating tomorrow's risks.