PracticeUpdate Dermatology May 2019

EXPERT OPINION 20

Tularemia’s Re-Emergence By Warren R. Heymann MD

Dr. Heymann is Professor of Medicine and Pediatrics, and Head of the Division of Dermatology at Cooper Medical School of Rowan University. He’s also the Clinical Professor of Dermatology at the Perelman School of Medicine of the University of Pennsylvania in Philadelphia, Pennsylvania.

P racticing dermatology is humbling business. I tip my hat to Coates et al, who diagnosed tularemia in an 11-year-old girl presenting with targetoid papules and plaques of her face, trunk, and extremities (diagnosed as erythema multiforme minor). 1 This was in the setting of a soft tissue infec- tion of her right foot, manifested by plantar purpuric macules and a pustule on her fifth toe. The diag- nosis was confirmed by PCR; the girl responded to therapy with gentamycin, ciprofloxacin (discontinued because of pseudotumor cerebri) and streptomycin. The authors recommend considering uncommon infections in the differential diagnosis of erythema multiforme, especially when common triggers such as herpes simplex virus or Mycoplasma infections are not evident. “Given its rarity, diagnosing tularemia requires a high index of clinical suspicion.” You can say that again – almost certainly, I would have missed the diagnosis. The purpose of this commentary is to make sure that does not happen in the future. Tularemia (rabbit fever; Ohara’s disease) is a zoonotic disease caused by a small, non-motile, aerobic and fastidious gram-negative pleomorphic coccobacil- lus bacterium, Francisella tularensis . The organism is named for Edward Francis, a US public health surgeon who dedicated his life to researching the organism, and for Tulare County, California, where the syndrome was first described in ground squir- rels in 1911. This organism can infect humans and a diverse population of animals, including more than 200 species of wild and domestic mammals, with rabbits and hares most classically affected. Follow- ing an incubation period of 3 to 5 days (range, 1–21), infection with F. tularensis can display various clinical presentations, depending on the route of inocula- tion, the dose of the inoculum, and the virulence of the organism. Humans may become infected by insect (arthropod, tick, fly) bites (the main route of contamination), handling infected animal tissues or fluids, direct contact with or ingestion of contami- nated water, food, or soil, and inhalation of infective aerosols. All ages and both sexes appear to be equally susceptible to tularemia; selected activities

such as hunting, trapping, butchering, and farming are most likely to expose adult men. Although F. tula- rensis is extremely infectious, its transmission from person to person has not been recorded. 2,3 In the United States, infection is reported most fre- quently in the south central states of Arkansas, Missouri, and Oklahoma, although it is reported throughout the country sporadically. 3 There is evi- dence of a recent re-emergence of tularemia in Germany 4 and a concern for an increasing number of cases related to climate change, as is true with other vector-borne illnesses. Tularemia is consid- ered a Category A bioterrorism threat. 1 There are four recognized subspecies of F. tularen- sis , with F. tularensis type A causing the most severe disease and the most frequent disease in North America. A less severe disorder is associated with F. tularensis subspecies holarctica (type B) in other parts of the Northern Hemisphere, including wide- spread disease in Europe. In addition to variations in disease severity associated with each subtype, there may also be differences in antibiotic susceptibility, with a greater degree of fluoroquinolone suscepti- bility reported in F. tularensis subspecies holarctica (type B). 3

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