Bactéries Coxiella burnetii
3 min

Gaining a better understanding of the genome of the bacterium responsible for Q fever

ANSES's Sophia Antipolis Laboratory has participated in a vast genetic analysis of strains of Coxiella burnetii, the bacterium responsible for Q fever, a disease that can be transmitted to humans. This collaboration between animal and human disease specialists, on which a paper was published in late 2022, is the first step in a One Health project on this zoonosis.

Q fever can be transmitted from animals to humans, where it can cause a severe flu-like illness with possible liver or lung complications.  In rare cases, the disease may become chronic and cause conditions such as endocarditis or chronic fatigue syndrome. The main reservoirs of this zoonosis are ruminant farms. This is the main source of infection for humans, with human-to-human transmission of Q fever being rare.

A collaboration involving both animal and human health

The study, published in November 2022 in the journal Frontiers in Microbiology, results from a collaboration between the Animal Q Fever Unit of ANSES's Sophia Antipolis Laboratory, which is both the national reference laboratory (NRL) and World Organisation for Animal Health (WOAH) reference laboratory, and the national reference centre (NRC) for Q fever hosted by the Méditerranée Infection University Hospital Institute in Marseille. The NRL is responsible for the animal aspects of Q fever, while the NRC focuses on the human side.

ANSES provided whole genome sequences of C. burnetii strains isolated from ruminants. These strains were added to the collection of patient-derived bacteria held by the NRC. The research carried out by the two partners constitutes the world's most comprehensive genetic analysis of Coxiella burnetii: 75 genomes were sequenced, including 65 new ones.

By comparing the genomes of all the strains, the bacterium's pangenome was obtained, i.e. the parts of the genome common to all strains. The researchers also deciphered specific parts of certain strains and showed that some were linked to particular clinical signs or geographical areas.

Better understanding the risks of transmission and exposure  

"This work is the first step in a long-term project on Q fever," explains Elodie Rousset, deputy head of the Animal Q Fever Unit and head of the NRL. "In 2020, we signed an agreement with the national reference centre to strengthen the One Health approach to Q fever work. We are seeking new methods to facilitate the isolation and sequencing of C. burnetii strains, because the bacterium has so far been difficult to isolate and cultivate."

ANSES is also working closely with a team from INRAE, the joint research unit for Epidemiology of animal and zoonotic diseases. This collaboration aims to continue increasing the strain collections, in particular to obtain Coxiella burnetii strains isolated from patients and farms in the same geographical area. This will lead to a better understanding of transmission scenarios and exposure risks, enable the rapid detection of certain hyper-virulent or hyper-disseminable strains, and, if necessary, enable the origin of any outbreak to be traced. 

In this regard, the Animal Q Fever Unit is also involved in the European Q-Net-Assess project, which will begin with six other organisations from six different countries. It aims to develop and share harmonised methodologies, from the collection of field samples through to the genetic analysis of strains, in order to build a large European-scale epidemiological and genetic database of Coxiella burnetii strains. With its international WOAH reference mandate, ANSES's Animal Q Fever Unit can position itself as a key partner in these European and international projects.