Sheep tick (Ixodes ricinus). © INRA, CHAUBET Bernard

Tick-fighting tactics

By Pascale Mollier, translated by Jessica Pearce
Updated on 06/20/2017
Published on 03/16/2016

Ticks vector major diseases in animals, including humans. They represent an ever greater threat. This report highlights key discoveries by INRA researchers related to these tiny invertebrates that have a disproportionately large influence on disease transmission.

The world’s number one vector of animal diseases

Ticks are the globe’s primary vector of animal diseases. For diseases afflicting humans, they rank second behind mosquitoes. For instance, they transmit the bacterium that causes Lyme disease, of which there are at least 25,000 new cases each year in France. They also vector the virus that causes tick-borne encephalitis (TBE) and the bacterium responsible for human granulocytotropic anaplasmosis (HGA) (1). In livestock, tick-borne pathogens (e.g., the protists that cause babesiosis and theileriosis [2]) can significantly hamper production.

(1) Granulocytotropic anaplasmosis: an emerging disease caused by a zoonotic bacterium; the illness is characterized by severe, generalized flu-like symptoms
(2) Theileriosis: cattle disease of major economic importance caused by endoparasites in the genus Theileria

A growing threat

Most of the time, a single tick carries several transmittable pathogens. Furthermore, in France, tick abundance is swelling in response to the increased abundances of certain wild host species, such as the European roe deer. Ticks are particularly numerous in eastern France. The vector for TBE, a major disease in eastern Europe, has been detected in ticks in Alsace. And what will happen with the virus responsible for Crimean-Congo hemorrhagic fever (CCHF), whose symptoms resemble those of Ebola and which has been detected in Turkey? Evidence suggests that European ticks, which are generalist vectors, should theoretically be able to transmit the CCHF virus to local animal and human populations, thus contributing to its broader propagation.

Hard to study

Ticks are hard to study. They have a complex life cycle that involves multiple hosts, and their blood meals can last up to 12 days. These two features make it challenging to raise ticks in the laboratory.

Diagram of Ixodes ricinus life cycle. © INRA
Diagram of Ixodes ricinus life cycle © INRA

INRA researchers have been responsible for several major tick-related discoveries and advances, which are highlighted in this report:

  • the development of a tick-rearing system that uses membranes instead of animal hosts
  • the identification of tick genes implicated in pathogen transmission
  • the identification of novel pathogens vectored by ticks, namely Bartonella species
  • the high-throughput sequencing of the tick microbiota: bacteria, viruses, and protists
  • the establishment of a genome-sequencing project focused on Europe’s most common tick species: Ixodes ricinus
  • the sequencing of the Babesia parasitic protist transmitted by ticks
  • the role of the Siberian chipmunk in Lyme disease transmission