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It’s mid-February when an otherwise healthy 42-year-old stockbroker presents to your office with fever, chills, and malaise. He reports no sick contacts, no exotic travel but mentions having spent the previous weekend on a fruitful hunting trip that included shooting and trapping rabbits. CXR reveals hilar adenopathy. Your differential includes influenza, tuberculosis, sarcoidosis, histoplasmosis, and tularemia. What should you do?

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A gram-negative coccobacillus, tularemia was first identified in 1911 by a scientist investigating an outbreak of what was initially thought to be bubonic plague in Tulare County, California. The disease has multiple means of transmission, and waterborne epidemics were seen in Europe and the Soviet Union in and around World War II (WWII). It has been suggested that the Soviet outbreak, which occurred at the Eastern front during WWII, was a result of a deliberate biological attack by the Russians. In fact, tularemia has been a favorite agent for bioweapons research since the 1930s. In 1969, the World Health Organization (WHO) estimated that 10 kg (20 lb) of aerosolized F. tularensis could infect 50,000 people, killing approximately 4,000. These numbers may be outdated because antibiotic and vaccine-resistant strains of weaponized tularemia—reported to have been developed at Biopreparat—would be far more deadly.

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Introduction

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Francisella tularensis, the causative agent of tularemia, is a small, nonmotile, facultative aerobic, intracellular gram-negative coccobacilli. Tularemia grows in aerobic environments. Despite its inability to form spores, it is nonetheless quite hardy and able to persist for several weeks in water, soil, vegetation, or in animal products. F. tularensis has three different species of which biovar tularensis is the most virulent form, and it is the one most commonly seen in the United States. The organism is considered to be one of the most communicable bacterial pathogens known. Disease hosts include rabbits, rats, and other small mammals that attain the infection through direct contact or by insect vectors, such as ticks and mosquitoes.

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Figure 16–1
Graphic Jump Location

Rabbits and other small mammals act as vectors for tularemia.

Photo provided by PDPhoto.org.

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Epidemiology

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F. tularensis is found worldwide, though global disease incidence has not been determined. Tularemia occurs sporadically throughout the continental United States, but predominantly in the rural areas of the South, Southwest, or Midwest. Since the 1990s, fewer than 200 cases are reported annually and occur in a bimodal seasonal pattern. The majority of cases are diagnosed in the summer/fall and are thought to be secondary to arthropod (tick) transmission. A smaller fall/winter peak coincides with hunting seasons. Most cases are secondary to direct contact of some kind, although there are infrequent cases of infection from inhalation. No significant differences in infection patterns are seen by age or by gender. Overall mortality rates prior to the advent of antibiotics ran between 5% and 15%, and for pneumonic forms between 30% and 60%. In the ...

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