A previously healthy 23-year-old man comes to the office due to abrupt-onset high fever, chills, headache, and weakness that developed after he spent a month working on a large ranch. His initial symptoms were quickly followed by intensely painful swellings in the groin. Physical examination is significant for tender and enlarged inguinal lymph nodes with overlying erythematous skin. Blood cultures and fluid aspirated from the lymph nodes grow gram-negative coccobacilli that resemble a closed safety pin on special staining. Which of the following activities is the most likely source of this patient's infection?
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Epidemiology |
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This patient's acute febrile illness with tender, erythematous inguinal lymphadenopathy likely indicates bubonic plague, a zoonotic infection endemic to North/South America, Africa, Asia, and Russia. The causative pathogen is Yersinia pestis, a small gram-negative bacillus/coccobacillus that exhibits bipolar staining (resembling a safety pin) on Giemsa or Wright stain. Although many small mammals harbor the bacteria, rodents (eg, rats) are the primary environmental reservoir. Transmission most often occurs when a flea that fed on an infected rodent regurgitates the bacteria while biting a human. Therefore, the most likely source of this patient's infection is close contact with rodent-infested areas (eg, changing rodent traps).
After cutaneous inoculation, Y pestis travels via lymphatic channels to regional lymph nodes and triggers a significant inflammatory reaction. Manifestations typically begin with acute fever, chills, weakness, and headache; buboes (painful, swollen, erythematous lymph nodes) develop shortly thereafter. Prompt treatment with an antibiotic (eg, aminoglycoside) is generally curative.
(Choices A and F) Brucellosis most often develops following consumption of unpasteurized animal products (eg, sheep milk) or contact with infected animals (eg, cattle, pigs, sheep, goats). Manifestations (eg, fever, night sweats, arthralgias) progress slowly and are often nonspecific, but painful regional lymphadenitis would be atypical; in addition, microscopic examination would reveal small, intracellular gram-negative rods.
(Choice B) The handling of animal hides can transmit anthrax, which often causes systemic symptoms and regional lymphadenitis. However, patients usually have a large necrotic skin ulcer with central eschar and surrounding erythema at the inoculation site. In addition, Bacillus anthracis, the causative agent, is a gram-positive, spore-forming rod.
(Choice C) Hunting and skinning small mammals (eg, rabbits, squirrels) is a common cause of tularemia, which often presents with painful regional lymphadenitis and fever. However, patients usually develop a papular lesion at the inoculation site that ulcerates. Although Francisella tularensis, the causative pathogen, is also a gram-negative coccobacillus, it is not associated with bipolar staining.
(Choice D) Cleaning a chicken coop can transmit Histoplasma capsulatum, a dimorphic fungus that primarily resides in soil contaminated with bird or bat droppings. Most cases present with pulmonary infiltrates, mediastinal/hilar lymphadenopathy, and systemic symptoms. Regional lymphadenitis would be uncommon; in addition, the organism is a fungus, not a coccobacillus.
Educational objective:
Bubonic plague causes a febrile illness with regional inflammatory lymphadenopathy (buboes). The underlying pathogen is Yersinia pestis, a small gram-negative bacillus/coccobacillus that exhibits bipolar staining (resembling a closed safety pin). The major environmental reservoir is rodents; transmission usually occurs via rodent fleabite.