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Tularemia Cases in Colorado

By Amesh A. Adalja, MD, FACP, FACEP, September 26, 2014

Recent reports of several cases of tularemia in Colorado should prompt clinicians to consider tularemia as a diagnostic possibility in the right context.Of diseases caused by category A bioterrorism agents, tularemia is the one that causes the highest number of natural cases in the United States. This disease, caused by the bacterium Francisella tularensis, is endemic in parts of the country, and approximately 100 to 200 cases occur annually.2

In 4 Colorado Counties

Beginning in July of this year, several cases of tularemia have been diagnosed in 4 Colorado counties, an increase from baseline rates. Several animal species have also tested positive in the affected counties.3 Tularemia is a zoonotic infection in which the pathogen spills from host species, such as rabbits, to humans through arthropod vectors, such as ticks or biting flies. This can occur through contact with the body fluids of host animals during butchering, by ingesting contaminated foods, or through aerosolization.

Several Forms, Low Infectious Dose

There are several forms of tularemia. The most common form is the ulceroglandular form, in which an ulcer and associated lymphadenopathy develop after exposure. More severe forms of tularemia include the pneumonic and typhoidal forms.3

The interest in tularemia as a biological weapon stems from the fact that a very low inhalational dose of organisms (~10) is all that is required to cause infection. This low infectious dose also means that laboratory workers should be alerted to the possibility of tularemia when diagnostic specimens are submitted.3

Diagnosis and Treatment

Tularemia, outside of its ulcerative forms, can be difficult to distinguish from other illnesses, and therefore diagnosis may be delayed. Routine cultures (with enriched media), biopsy specimens, and serologic testing may aid diagnosis, but clinical suspicion will likely guide diagnosis, especially in endemic areas such as Missouri and Martha’s Vineyard (MA).

The mainstay of treatment for tularemia is antibiotic therapy with gentamicin or streptomycin. Doxycycline or ciprofloxacin can be used for postexposure prophylaxis. No vaccine or rapid diagnostic test is available.3

Astute Clinicians

The cluster of tularemia cases in Colorado should serve to remind physicians that, though relatively rare, tularemia does occur naturally in this country. As prompt diagnosis—in the absence of a rapid diagnostic test—and treatment of this potentially serious illness are required to forestall complications, the astuteness of clinicians in detecting its presence will be key.


  1. Handy RM. First human case of tularemia reported in Weld county. Coloradoan September 23, 2014. Accessed September 20, 2014.
  2. Centers for Disease Control and Prevention (CDC). Tularemia—United States, 1990-2000. MMWR Morb Mortal Wkly Rep 2002;51(9):181-184.
  3. Dennis DT, Inglesby TV, Henderson DA, et al. Consensus statement: tularemia as a biological weapon: medical and public health management. JAMA 2001;285(21):2763-2773.