Elmer Fudd beware: Tularemia’s re-emergence
Sept. 24, 2018
Practicing dermatology is humbling business. I tip my hat to Polat 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). This was in the setting of a soft tissue infection of her right foot, manifested by plantar purpuric macules and a pustule of her fifth toe. The diagnosis 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.” (1)
You can say that again — almost certainly, I would have missed the diagnosis.
The purpose of this commentary is 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 coccobacillus bacterium, F. 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 squirrels 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 associated. Following an incubation period of 3 to 5 days (range, 1 to 21), infection with F. tularensis can display various clinical presentations, depending on the route of inoculation, 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 contaminated 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. tularensis is extremely infectious, its transmission from person to person has not been recorded. (2,3)
In the United States, infection is reported most frequently in the south central states of Arkansas, Missouri, and Oklahoma, although it is reported throughout the country sporadically. (3) There is evidence of a recent re-emergence of tularemia in Germany (4), and a concern for an increasing number of cases related to climate change, as in other vector-borne illnesses. Tularemia is considered at Category A bioterrorism threat. (1)
There are four recognized subspecies of F. tularensis, 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 widespread 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 susceptibility reported in F. tularensis subspecies holarctica (type B). (3)
Depending on the transmission route, 6 clinical types tularemia have been described: glandular, ulceroglandular, oculoglandular, oropharyngeal, typhoidal and pulmonary disease. The most common clinical type is the ulceroglandular type, whereas oculoglandular tularaemia is very rare. However, the most common clinical type in Turkey and Europe is the oropharyngeal type. Polat et al, in their review of 168 cases of tularemia from Turkey fount that 149 (88.69%) had the oropharyngeal type, 12 (7.73%) had the ulceroglandular type, 5 (2.9%) had the oculoglandular type and 2 (0.59%) had the pulmonary type. Secondary skin manifestations were found in 26 patients (15.47%). Sweet syndrome (SS) was found in 11 patients (6.54%), most of whom presented with the oropharyngeal form, while erythema nodosum (EN) was found in 7 patients (4.16%), dermatitis in 2 (1.19%), urticaria in 2 (1.19%), acneiform eruptions in 1 (0.59%), vasculitis‐like eruptions in 1 (0.59%) and SS + EN in 1 (0.59%). Patients with the oropharyngeal form had a statistically significant (P < 0.001) higher number of skin findings than patients with the other forms. The authors concluded that dermatologists working in endemic regions must be aware of the varied clinical presentations of tularemia. (5)
The diagnosis of tularemia may be confirmed serologically (although early testing may be negative), culture (warning the laboratory to prevent accidental inhalation and pneumonic tularemia in laboratory workers) (3), or by PCR. (1) Therapy focuses on aminoglycosides and fluroquinolones; caution is advised regarding tetracyclines (because of they are bacteriostatic, there is a high relapse rate upon discontinuation). Incision and drainage of involved lymph nodes may be necessary. (3) Because of the concern of tularemia as a bioterrorist threat, there is current research on developing a vaccine for general use. (6)
A diagnosis cannot be made unless it is thought of. While I hope to never see tularemia, especially if due to bioterrorism, hopefully I will recognize it if need be.
Point to remember: Tularemia may be present a primary dermatological disease (such as the ulceroglandular form), with or without secondary dermatoses (erythema multiforme, Sweet syndrome, erythema nodosum).
1. Coates SJ, et al. Tularemia-induced erythema multiforme minor in an 11-year-old girl. Pediatr Dermatol 2018; 35: 478-81.
2. Stidham RA, et al. Epidemiological review of Francisella tularensis: A case study in the complications of dual diseases. PLoS Curr 2018; Jan 18; 10.
3. Snowden J, Simonsen KA. Tularemia. StatPearls [Internet). Jan 2017 May 26.
4. Faber M, et al. Tularemia in Germany – A re-emerging zoonosis. Front Cell Infect Microbiol 2018; 8:40.
5. Polat M, et al. Dermatological aspects of tularemia: A study of 168 cases. Clin Exp Dermatol 2018; May 14 [Epub ahead of print].
6. Putzova D, et al. Tularemia vaccines. Folia Microbiol 2016; 61: 495-504.
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