Tularemia as a waterborne disease: a review

Abstract

Francisella tularensis is a Gram-negative, intracellular bacterium causing the zoonosis tularemia. This highly infectious microorganism is considered a potential biological threat agent. Humans are usually infected through direct contact with the animal reservoir and tick bites. However, tularemia cases also occur after contact with a contaminated hydro-telluric environment. Water-borne tularemia outbreaks and sporadic cases have occurred worldwide in the last decades, with specific clinical and epidemiological traits. These infections represent a major public health and military challenge. Human contaminations have occurred through consumption or use of F. tularensis -contaminated water, and various aquatic activities such as swimming, canyoning and fishing. In addition, in Sweden and Finland, mosquitoes are primary vectors of tularemia due to infection of mosquito larvae in contaminated aquatic environments. The mechanisms of F. tularensis survival in water may include the formation of biofilms, interactions with free-living amoebae, and the transition to a ‘viable but nonculturable' state, but the relative contribution of these possible mechanisms remains unknown. Many new aquatic species of Francisella have been characterized in recent years. F. tularensis likely shares with these species an ability of long-term survival in the aquatic environment, which has to be considered in terms of tularemia surveillance and control.

Francisella novicida and F. philomiragia biofilm features conditionning fitness in spring water and in presence of antibiotics

“…By providing the capacity of bacteria to survive in nutrient-limited aquatic environment, the biofilms could also contribute to the environmental persistence and thus indirectly promote the transmission of Francisella to hosts [13,23]. To adress this question, Francisella biofilms formed in microtiter plates were incubated in water at 4˚C and survival of bacterial was evaluated over time by CFU counting until no bacteria were recovered.…”

“…Although the epidemiology of this disease is still not fully understood, risk factors include exposure to arthropods, especially ticks which are the most important vectors of the terrestrial life cycle of Type A Francisella [1,19]. The two unusual outbreaks of pneumonic tularemia reported from the island of Martha's Vineyard [20,21] together with the observed prolonged survival of Type A F. tularensis in brackish-water collected on this island [22] allowed hypothesizing that the aquatic environment could serve as a reservoir for F. tularensis [13,23]. F. tularensis subsp.…”

“…While only a few cases of human infection with F. philomiragia have been described, they correlated with pneumonia in healthy individuals undergoing near-drowning accidents or in immunocompromised people. Overall, water appears as an important reservoir for some human pathogenic Francisella strains [23].…”

Canyoning Accidents in Austria from 2005 to 2018

“…As no microbiological samples were collected in our patients with gastrointestinal infections, it is unknown whether a specific pathogen was causative. Canyoning-related waterborne, infectious diseases, e.g., tularaemia and leptospirosis, have been described in warmer countries [3,6,16,17] and general practitioners, as well as hospital staff, should keep them in mind when treating patients who have practiced water-related activities [4,5]. Preventive measures, such as clothing for skin protection, are an option to prevent infectious diseases [17].…”

“…Typical pathologies, such as the 'Canyoning-Hand,' a form of contact dermatitis with skin lesions involving only the fingertips and palms, due to the cold, wet and rugged nature of canyoning, have been described [3]. In rare cases, infectious diseases, e.g., leptospirosis or tularemia, can also be canyoning-related and even occur as a local outbreak [4][5][6]. A study conducted in the Autonomous Community of Aragon, Spain, collected data for a ten-year period in a typical canyoning region [7].…”