Water and mosquitoes as key components of the infective cycle of Francisella tularensis in Europe: a review

Abstract

Francisella tularensis is the pathogen of tularemia, a zoonotic disease that have a broad range of hosts. Its epidemiology is related to aquatic environments, particularly in the subspecies holarctica. In this review, we explore the role of water and mosquitoes in the epidemiology of Francisella in Europe. F. tularensis epidemiology has been linked to natural waters, where its persistence has been associated with biofilm and amebas. In Sweden and Finland, the European countries where most human cases have been reported, mosquito bites are a main route of transmission. F. tularensis is present in other European countries, but to date positive mosquitoes have not been found. Biofilm and amebas are potential sources of Francisella for mosquito larvae, however, mosquito vector capacity has not been demonstrated experimentally, with the need to be studied using local species to uncover a potential transmission adaptation. Transstadial, for persistence through life stages, and mechanical transmission, suggesting contaminated media as a source for infection, have been studied experimentally for mosquitoes, but their natural occurrence needs to be evaluated. It is important to clear up the role of different local mosquito species in the epidemiology of F. tularensis and their importance in all areas where tularemia is present.

Keywords:

• Aquatic reservoir
• biofilm
• protozoa
• tularemia
• vector borne

Acknowledgments

We would like to thank professor Önder Düzlu, from Erciyes University, for helping us retrieving Tularemia epidemiological data from Turkey. We would also like to thank the Master’s Degree in Zoonoses and One Health of the “Universitat Autònoma de Barcelona” (UAB), Barcelona, Spain (https://www.uab.cat/web/estudiar/official-master-s-degrees/general-information/zoonosis-and-one-health-1096480962610.html?param1=1345694246010); for allowing collaboration of two of the co-authors (Sara Jareño-Moreno and Clara Buch-Cardona) with their Master Thesis.

Disclosure statement

The authors report there are no competing interests to declare.

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work contributes to the project BOOMRAT (PID2019-109327RB-I00), funded by the “Plan Estatal de Investigación Científica y Técnica y de Innovación 2017-2020”, Ministry of Science and Innovation, Government of Spain, and the project ‘CLU-2019-01 – iuFOR Institute Unit of Excellence’ of the University of Valladolid, funded by the Junta de Castilla y León and co-financed by the European Union (ERDF ‘Europe drives our growth’). Herrera-Rodríguez was supported by a PhD studentship “Ayudas para contratos predoctorales para la formación de doctores 2020” (PRE2020-095385), funded by the Ministry of Science and Innovation, Government of Spain.