Tularemia in the world

Abstract

Here we review the data on the global spread of tularemia — a natural focal, especially dangerous human and animal infection caused by the bacterium Francisella tularensis. Strains of the most virulent F. tularensis subspecies tularensis circulate solely in the North America, whereas less virulent F. tularensis subspecies holarctica is found in Europe, Asia (Japan), North America, Australia (especially Tasmania). Isolates of this subspecies are isolated in territories of various climatic zones — from subarctic to subtropical, featured with diverse biocenoses in natural foci — from water to desert, with their unique hosts and carriers. Compared with the remaining subspecies of the tularemia causative agent, subspecies holarctica has a wide spread due to its ability to live in aquatic environment that markedly expands its distribution areas and shows higher ecological plasticity and stability. Infection of people by such causative agents occurs due to infected blood-sucking arthropods biting (mosquitoes, horseflies, ticks), intake of rodent-contaminated food and water, inhalation of air-dust aerosol bearing tularemia pathogen transmitted from sick rodents, as well as after direct contact with infected animals (hunting, pet care, carcass cutting). Different routes of the pathogen transmission in various countries are discussed. The peak prevalence of tularemia is observed in the North America (USA) and Europe (Sweden and Finland), as well as in Asia (Turkey). Since the mid-20th century, incidence rate of tularemia has been profoundly decreased in the Russian Federation and Kazakhstan due to preventing populations in tularemia-enzootic territories as well as those at risk of contact. In the last years, 31 European countries as well as Turkey and Japan have begun to conduct mandatory registration of tularemia cases due to an opportunity of using the pathogen for bioterrorism. The geographical distribution of the main tularemia microbe phylogenetic populations and subpopulations is demonstrated. The peak diversity of F. tularensis subsp. holarctica strains in a single country was registered in China. The major ecology- and epidemiology-related features of the tularemia causative agent are noted.