Tularemia: An Emerging Zoonosis in Children With Many Faces

Tularemia is a Holarctic zoonosis caused by Francisella tularensis, a highly infectious, nonspore-forming, aerobic, gram-negative coccobacillus. It may infect a wide range of hosts, including invertebrates, mammals, amphibians and birds. Human infection occurs through contact with infected animals, contaminated environments or via arthropod vectors. Tularemia is endemic throughout most of Europe, northern and central Asia, and North America. Although previously thought to be absent from the southern hemisphere, autochthonous human cases were documented in Tasmania in 2011. Francisella tularensis is regarded as a potential bioterrorism agent owing to its low infectious dose and multiple routes of transmission, including inhalation, arthropod bites, direct animal contact and ingestion of contaminated food or water.1 Human-to-human transmission has not been reported. Four subspecies of F. tularensis are recognized, of which 2 are clinically relevant. Francisella tularensis subsp. tularensis (type A) is the most virulent and occurs only in North America (United States and southern Canada), with ticks serving as important vectors. Type A is further divided into A-I and A-II. Within A-I, 2 sub-lineages are distinguished: A-Ia and the more virulent A-Ib, which exhibits greater intrinsic pathogenicity compared with A-Ia, A-II or type B strains. A-I occurs predominantly in the central and eastern United States, whereas A-II is more common in the western United States. In contrast, F. tularensis subsp. holarctica (type B) predominates in Europe and Asia, typically producing a milder clinical course characterized by localized disease forms. Mortality in treated cases is generally low (