Abstract
In 2018, the incidence of tularemia increased twofold in the west of France, with many pneumonic forms, suggesting environmental sources of infection. We investigated the presence of Francisella tularensis subsp. holarctica and other Francisella species DNA in the natural aquatic environment of this geographic area. Two sampling campaigns, in July 2019 and January 2020, allowed the collection of 87 water samples. Using a combination of real-time PCR assays, we tested the presence of either Francisella sp., F. tularensis/F. novicida, and F. tularensis subsp. holarctica, the latter being the only tularemia agent in Europe. Among 57 water samples of the first campaign, 15 (26.3%) were positive for Francisella sp., nine (15.8%) for F. tularensis and/or F. novicida, and four (7.0%) for F. tularensis subsp. holarctica. Ratios were 25/30 (83.3%), 24/30 (80.0%), and 4/30 (13.3%) for the second campaign. Among the thirty sites sampled during the two campaigns, nine were positive both times for Francisella sp., seven for F. tularensis and/or F. novicida, and one for F. tularensis subsp. holarctica. Altogether, our study reveals a high prevalence of Francisella sp. DNA (including the tularemia agent) in the studied aquatic environment. This aquatic environment could therefore participate in the endemicity of tularemia in the west of France.
Highlights
Published: 28 June 2021Francisella tularensis is a Gram-negative bacterium that causes the zoonosis tularemia.It is a highly virulent human pathogen classified in category A of potential agents of biological threat by the US Centers for Disease Control and Prevention (CDC) [1]
F. tularensis subsp. mediasiatica is restricted to central Asia and Russia, and has never been associated with human infections [4]
In 2018, tularemia incidence increased twofold in France, with 21% of pneumonic cases, while this clinical form usually represents less than 10% of reported tularemia cases
Summary
Francisella tularensis is a Gram-negative bacterium that causes the zoonosis tularemia. It is a highly virulent human pathogen classified in category A of potential agents of biological threat by the US Centers for Disease Control and Prevention (CDC) [1]. Four subspecies of F. tularensis are recognized. Two are associated with human tularemia: F. tularensis subsp. Tularensis (type A) is the most virulent, only present in North America; and F. tularensis subsp. Holarctica (type B) is less virulent, and located in all the northern hemisphere and Australia [2,3]. Mediasiatica is restricted to central Asia and Russia, and has never been associated with human infections [4].
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