Candidatus Neoehrlichia mikurensis in Bank Voles, France

Muriel Vayssier-Taussat

, Danielle Le Rhun, Jean-Philippe Buffet, Narimane Maaoui, Maxime Galan, Emmanuel Guivier, Nathalie Charbonnel, and Jean-François Cosson

Author affiliations: Author affiliations: Institut National de la Recherche Agronomique, Maisons-Alfort, France (M. Vayssier-Taussat, D. Le Rhun, J.-P. Buffet, N. Maaoui); Institut National de la Recherche Agronomique, Montferrier-sur-Lez, France (M. Galan, E. Guivier, N. Charbonnel, J.-F. Cosson)

Abstract

To further assess the geographic occurrence, possible vectors, and prevalence of Candidatus Neoehrlichia mikurensis, we analyzed spleen tissues from 276 voles trapped close to human settlements in France; 5 were infected with the organism. Sequencing showed the isolates carried the same genotype as the bacteria that caused disease in humans and animals elsewhere in Europe.

Emerging infectious diseases substantially affect public health. Analysis of a database of 335 emerging infectious disease events indicated that 60.0% were zoonotic diseases, most (71.8%) of which originated in wildlife, and that zoonoses are increasing over time (1). Half of these emerging infection events involved bacteria belonging, for the most part, to the proteobacterial order Rickettsiales (1).
In Western Europe, the widespread and abundant Ixodes ricinus tick is the most common vector for human and animal pathogens and is also a major vector of pathogens responsible for rodent-borne diseases (2). Lyme borreliosis (Lyme disease), which is caused by infection with the bacteria Borrelia burgdorferi sensu lato, is the most prevalent tick-borne and rodent-borne illness. However, persons bitten by ticks can also be infected by other bacteria belonging to 3 main genera: Anaplasma spp., Bartonella spp. and Rickettsiae spp. Over the past 10 years, these bacterial species have been associated with tick-borne infections in humans (2).
During the last decade, DNA of a new species of intracellular bacteria belonging to the family Anaplasmataceae was sequenced from isolates from ticks and rodents originating in Europe and Asia (3–5). The first isolate of this organism was obtained in 2004 from wild Rattus norvegicus rats and I. ovatus ticks from Japan (6). A comparison of the morphologic and molecular characterization of that isolate with earlier, closely related sequences in the GenBank database supported classification of the isolate in a novel genetic cluster within the family Anaplasmataceae; thus, the nomenclature “Candidatus Neoehrlichia mikurensis” was proposed for all current organisms in this group (6).
Since the 2004 discovery of Candidatus N. mikurensis, the bacterium has been identified in different tick species, including I. ricinus ticks in Europe, and in small rodents (other than R. norvegicus rats) suspected of being the main reservoir for the bacterium (7–10). In 2010, human infection with Candidatus N. mikurensis was reported in a Swedish patient (11). In that same year, infections were described in 5 persons in Germany, Switzerland, and the Czech Republic (12). More recently, Candidatus N. mikurensis infection was reported in a dog in Germany (13). Signs and symptoms described in all cases were general and nonspecific (e.g., fever, cough, anemia, headache, pulmonary infiltrate, malaise, myalgia, joint pain, extreme fatigue, erythema), making diagnosis difficult, particularly in the absence of serologic tests. Thus, it is likely that the actual incidence of human Candidatus N. mikurensis infection in Europe is much higher than currently reported.
Previous studies of Candidatus N. mikurensis in Europe have advocated for an assessment of the geographic occurrence, possible vectors, and prevalence of this microorganism. In this study we demonstrate the presence of Candidatus N. mikurensis in France, specifically in the bank vole (Myodes glareolus), a suspected reservoir for the microorganism.