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

Tick-fighting tactics

Novel bacteria detected in patients bitten by ticks

INRA researchers* and their collaborators** isolated and identified novel Bartonella species originating from wild animal species in the blood of patients who had been bitten by ticks. These results were published on March 1, 2016 in the journal Emerging Infectious Diseases.

Ticks: a threat to human and animal health

Ticks are blood-feeding arthropods that consume several meals over the course of their life cycle, which includes a larval, nymphal, and adult stage; their hosts are vertebrates and include humans. As they feed, they may inadvertently become infected with pathogens found in the host’s blood. They may then transmit these pathogens to other hosts over the course of future meals.

Ticks pose a real threat to human and livestock health. In Europe, they are the number one vector of infectious diseases in animals. In particular, they transmit Lyme disease to humans. Lyme disease is caused by bacteria belonging to the Borrelia burgdorferii species complex. Each year, 85,000 new cases of Lyme disease occur in Europe. Ticks transmit other bacteria—as well as viruses and protists—that also cause disease in animals, including humans. In livestock, tick-borne diseases, such as babesiosis and anaplasmosis, can seriously hamper production. Yet, tick-borne pathogens remain poorly characterized and the diseases they cause are often misdiagnosed.

On the lookout for tick-borne pathogens

A certain number of patients suffer from unexplained, clinically vague symptoms following tick bites, but their test results come back negative for Lyme disease.

In collaboration with other researchers, INRA scientists examined samples from such patients for the presence of Bartonella bacteria. Some results came back positive. It appeared that the ticks were the culprits as they were found to carry Bartonella species and could transmit the bacteria to hosts during blood meals.

Ticks found to vector Bartonella bacteria

Blood samples were taken from 66 patients residing all over France. When the samples were cultured in the lab, six gave rise to Bartonella bacteria. Researchers then sequenced the genomes of the six isolates.

They found that three isolates belonged to the species Bartonella henselae, which is hosted by cats and causes cat-scratch disease. The other three isolates were associated with wild animal hosts and had never before been observed in humans: Bartonella doshiae, typically found in voles and field mice; Bartonella tribocorum, found in rats; and Bartonella schoenbuchensis, found in deer.

This is the first time Bartonella species normally hosted by wild animals have been found in humans bitten by ticks. Thanks to these findings, it is now possible to develop medical treatments adapted to these specific bacteria. More generally, this work will help improve diagnostic techniques for tick-borne diseases.

This research was funded by the European Union (COST action EurNegVec and EDENext project).

*Joint Research Unit for Parasite and Fungus Immunology and Molecular Biology (INRA/ANSES/ENVA)
**National Reference Center for Rickettsia, Coxiella, and Bartonella (Méditerranée Infection Foundation) and Joint Research Unit on Emerging Tropical Diseases (IRD/INSERM/AMU)

Reference

Muriel Vayssier-Taussat, Sara Moutailler, Françoise Féménia, Philippe Raymond, Olivier Croce, Bernard La Scola, Pierre Edouard Fournier and Didier Raoult. Identification of Novel Zoonotic Activity of Bartonella spp.. Emerging Infectious Diseases. March 2016, Volume 22, number 3.

The publication is accessible on the Centers for Disease Control and Prevention (CDC) website: http://wwwnc.cdc.gov/eid/article/22/3/15-0269_article