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

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.土拉弗朗西斯菌（Francisella tularensis）是土拉菌病（tularemia）的病原菌，该疾病是一种宿主范围广泛的人畜共患病。其流行病学特征与水生环境紧密相关，该关联在霍尔塔亚种（subspecies holarctica）中尤为显著。本综述旨在探讨水与蚊虫在欧洲地区土拉弗朗西斯菌流行病学中的作用。土拉弗朗西斯菌的流行病学与天然水体存在关联，其在水体中的持续存活与生物膜（biofilm）和阿米巴原虫（amebas）密切相关。在报告人类感染病例最多的欧洲国家瑞典与芬兰，蚊虫叮咬是土拉菌病的主要传播途径。欧洲其他国家虽也存在土拉弗朗西斯菌，但迄今尚未在蚊虫体内检测到阳性菌株。生物膜与阿米巴原虫是蚊虫幼虫感染土拉弗朗西斯菌的潜在来源，但目前尚未通过实验证实蚊虫的媒介传播能力，需采用当地蚊虫物种开展研究，以揭示其潜在的传播适应性。已有实验针对蚊虫开展了经变态传播（即通过各生活阶段持续留存病原体）与机械性传播（即以污染介质作为感染源）的相关研究，但二者的自然发生情况仍有待评估。明确不同本地蚊虫物种在土拉弗朗西斯菌流行病学中的作用，以及其在所有土拉菌病流行区域的重要性，具有重要意义。