Abstract & Commentary
Synopsis: A child developed tularemia after being bitten by a pet hamster.
Source: CDC. Brief Report: Tularemia Associated With a Hamster Bite—Colorado, 2004. MMWR. 2005;53:1202-1203.
A Colorado family purchased 6 hamsters from a pet store, all of whom died within a week from a diarrheal illness. One, however, managed to bite a 3-year-old child on the index finger before dying. One week later, the child developed fever and painful left axillary lymphadenopathy, as well as sloughing of skin at the site of the bite. The child was given amoxicillin/clavulanic acid without success, and 7 weeks after the onset of illness, the left axillary lymph node was excised. Francisella tularensis was recovered from the tissue, and the patient was found to have a convalescent titer to this organism of 1:4096. He was successfully treated with ciprofloxacin.
Comment by Stan Deresinski, MD, FACP
Francisella tularensis is a small, aerobic, catalase-positive, pleomorphic, Gram-negative coccobacillus. It is infrequently detected in Gram stains of clinical material. In addition, its growth in culture requires the presence of a sulfhydryl source and, as a consequence, it will not be recovered on most routinely used solid media in the absence of supplementation. As a consequence, its isolation requires a high index of clinical suspicion, which is important to communicate to the clinical microbiology laboratory. This communication is also of importance because the organism presents a significant biohazard in the laboratory. Infection may be confirmed with serological studies.
While F. tularensis infects a large spectrum of both vertebrates and invertebrates, rabbits and rodents are most important. Transmission to humans occurs most frequently as the result of contact with contaminated animal products or insect bite, although it may also occur via aerosol, contact with contaminated environment or, as in the case summarized here, via animal bites. In experimental systems, as few as 10 organisms are capable of causing disease.
Although overlap of the syndromes is not uncommon, 6 clinical forms of tularemia are typically described: ulceroglandular, glandular, oculoglandular, pharyngeal, typhoidal, and pneumonic. The child whose illness is summarized here would be classified as having the glandular form. The axilla is the most frequent site of adenopathy in rabbit-associated human tularemia, while the inguinal lymph nodes are most frequently involved in tick-associated disease—presumably reflecting the lymphatic drainage of the sites of inoculation.
Texts still recommend streptomycin as the treatment of choice for patients with tularemia, with gentamicin as an alternative. Doxycycline therapy has apparently been associated with failures. The organism is susceptible in vitro to fluoroquinolones, and ciprofloxacin therapy was successful in the case reviewed here.
Dr. Deresinski, MD, FACP, is Clinical Professor of Medicine at Stanford University and Associate Chief of Infectious Diseases at Santa Clara Valley Medical Center.