The Recent Evolution of a Maternally-Inherited Endosymbiont of Ticks Led to the Emergence of the Q Fever Pathogen, Coxiella burnetii

International audienceQ fever is a highly infectious disease with a worldwide distribution. Its causative agent, the intracellular bacterium Coxiella burnetii, infects a variety of vertebrate species, including humans. Its evolutionary origin remains almost entirely unknown and uncertainty persists regarding the identity and lifestyle of its ancestors. A few tick species were recently found to harbor maternally-inherited Coxiella-like organisms engaged in symbiotic interactions, but their relationships to the Q fever pathogen remain unclear. Here, we extensively sampled ticks, identifying new and atypical Coxiella strains from 40 of 58 examined species, and used this data to infer the evolutionary processes leading to the emergence of C. burnetii. Phylogenetic analyses of multi-locus typing and whole-genome sequencing data revealed that Coxiella-like organisms represent an ancient and monophyletic group allied to ticks. Remarkably, all known C. burnetii strains originate within this group and are the descendants of a Coxiella-like progenitor hosted by ticks. Using both colony-reared and field-collected gravid females, we further establish the presence of highly efficient maternal transmission of these Coxiella-like organisms in four examined tick species, a pattern coherent with an endosymbiotic lifestyle. Our laboratory culture assays also showed that these Coxiella-like organisms were not amenable to culture in the vertebrate cell environment, suggesting different metabolic requirements compared to C. burnetii. Altogether, this corpus of data demonstrates that C. burnetii recently evolved from an inherited symbiont of ticks which succeeded in infecting vertebrate cells, likely by the acquisition of novel virulence factors

Prevalence and molecular typing of Coxiella burnetii in bulk tank milk in Belgian dairy goats, 2009-2013.

&lt;p&gt;Q fever, a worldwide zoonosis, is an arousing public health concern in many countries since the recent Dutch outbreak. An emerging C. burnetii clone, genotype CbNL01, was identified as responsible for the Dutch human Q fever cluster cases. Since 2009, Q fever surveillance in the goat industry was implemented by the Belgian authorities. The herd prevalence (December 2009-March 2013) ranged between 6.3 and 12.1%. Genotypic analysis highlighted the molecular diversity of the Belgian strains from goats and identified an emerging CbNL01-like genotype. This follow-up allowed the description of shedding profiles in positive farms which was either continuous (type I) and associated to the CbNL01-like genotype; or intermittent (type II) and linked to other genotypes. Despite the circulation of a CbNL01-like strain, the number of notified Belgian human cases was very low. The mandatory vaccination (in June 2011) on positive dairy goat farms in Belgium, contributed to a decrease in shedding.&lt;/p&gt;</p

Mycobacterium avium subsp paratuberculosis in lake catchments, in river water abstracted for domestic use, and in effluent from domestic sewage treatments works: Diverse opportunities for environmental cycling and human exposure

Mycobacterium avium subsp. paratuberculosis from infected animals enters surface waters and rivers in runoff from contaminated pastures. We studied the River Tywi in South Wales, United Kingdom, whose catchment comprises 1,100 km2 containing more than a million dairy and beef cattle and more than 1.3 million sheep. The River Tywi is abstracted for the domestic water supply. Between August 2002 and April 2003, 48 of 70 (68.8%) twice-weekly river water samples tested positive by IS900 PCR. In river water, the organisms were associated with a suspended solid which was depleted by the water treatment process. Disposal of contaminated slurry back onto the land established a cycle of environmental persistence. A concentrate from 100 liters of finished water tested negative, but 1 of 54 domestic cold water tanks tested positive, indicating the potential for these pathogens to access domestic outlets. In the separate English Lake District region, with hills up to 980 m, tests for M. avium subsp. paratuberculosis in the high hill lakes and sediments were usually negative, but streams and sediments became positive lower down the catchment. Sediments from 9 of 10 major lakes receiving inflow from these catchments were positive, with sediment cores indicating deposition over at least 40 to 50 years. Two of 12 monthly 1-liter samples of effluent and a single 100-liter sample from the Ambleside sewage treatment works were positive for M. avium subsp. paratuberculosis. Since Lake Ambleside discharges into Lake Windermere, which is available for domestic supply, there is a potential for these organisms to cycle within human populations

Experimental and theoretical evaluation of typing methods based upon random amplification of genomic restriction fragments (AFLP) for bacterial population genetics

The reliability and the level of taxonomie resolution of the amplified fragment length polymorphism (AFLP) method were evaluated with species of patho-genic bacteria involved in human, animal and plant diseases. The method was found to be very versatile as it can be adapted to the individual genome constraints of all tested species. The calculation of a genetic distance d corresponding to the average dissimilarity between actual overall genome sequences was proposed for comparing AFLP data. Bacterial models showed clearly different patterns between strains be-longing to different genomic species, while patterns were clearly similar within a given species. The threshold which distinguishes between inter and infra-specific distances indicates a critical overall genome diversity of about 14% (d = 0.14). AFLP had more resolution power than serology, phage typing, PFGE and restriction analysis of ribosomal intergenic spacers. In the latter case, regression analysis showed that PCR-RFLP of ribosomal intergenic spacers can only be used to differentiate bacteria which have at least 3.4% (d — 0.034) nucleotide differences between their respec-tive genomes. Finally, an improved procedure using newly developed software was also proposed in order to standardize the capture of reliable data and their numeric treatment for the future development of AFLP data bases.La reproductibilité et Ie niveau de resolution taxo-nomique de ramplification aléatoire de fragments de restriction (AFLP) ont été éval-ués avec divers modèles pathogènes de l’homme, des animaux et des plantes. La methode est tres adaptable et peut être modifiée en fonction des particularités génomiques de chaque espèce. La différence nucléotidique moyenne réelle entre les genomes est une mesure de la distance génomique entre bactéries qui peut être estimée a partir de l’AFLP. Cette mesure permet la comparaison de données AFLP obtenues de fagons différentes. Avec la plupart des modèles, Ie seuil discriminant les distances interdes distances infra-spécifiques correspond a des differences nucléotidiques de l’ordre de 14% (d — 0,14). L’AFLP s’est montrée plus résolutive que la sérologie, la lyso-typie, l’électrophorèse en champs pulsés, et la PCR-RFLP de l’intergène ribosomique. L’analyse montre ainsi que la PCR-RFLP de l’intergène ribosomique permet de dis-tinguer des bactéries présentant au moins 3,4% (d = 0,034) de differences entre leurs genomes respectifs. Une procédure Standard d’aquisition et de traitement numérique des données incluant des logiciels adaptés est également proposée