A previously healthy 23-year-old man comes to the office due to abrupt-onset high fever, chills, headache, and weakness that developed during a hiking and camping trip in New Mexico. His initial symptoms were quickly followed by intensely painful swellings in the groin. Physical examination shows tender and enlarged inguinal lymph nodes with overlying erythematous skin. Blood cultures and fluid aspirated from the lymph nodes grow gram-negative coccobacilli, which resemble a closed safety pin on special staining. Which of the following are the most likely source of this patient's infection?

Question

A previously healthy 23-year-old man comes to the office due to abrupt-onset high fever, chills, headache, and weakness that developed during a hiking and camping trip in New Mexico.  His initial symptoms were quickly followed by intensely painful swellings in the groin.  Physical examination shows tender and enlarged inguinal lymph nodes with overlying erythematous skin.  Blood cultures and fluid aspirated from the lymph nodes grow gram-negative coccobacilli, which resemble a closed safety pin on special staining.  Which of the following are the most likely source of this patient's infection?

Quizplus · Accepted Answer

This patient's acute febrile illness with tender, erythematous inguinal lymphadenopathy likely indicates bubonic plague, a zoonotic infection endemic to the Southwestern United States (eg, New Mexico). The causative pathogen is Yersinia pestis, a gram-negative coccobacillus that exhibits bipolar staining (resembling a safety pin) on Giemsa or Wright stain. Although many small mammals can harbor the bacteria, rodents (eg, rats) are the primary environmental reservoir. Transmission to humans primarily occurs via rodent flea bite. Following cutaneous injection, the organism travels 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. Treatment with antibiotics (eg, aminoglycoside) is generally curative. (Choice A) Bats can transmit rabies, which is characterized by nonspecific symptoms (eg, fever, myalgias, malaise) followed by hydrophobia, pharyngeal spasms, hyperactivity, coma, and death. Rabies is caused by a virus (Lyssavirus), not a gram-negative coccobacillus. (Choice B) Non-typhoidal Salmonella, a motile gram-negative bacillus, is often transmitted via the ingestion of contaminated poultry. It causes febrile ("pea soup") diarrhea, not acute regional inflammatory lymphadenopathy. (Choice D) Sheep hides can transmit anthrax, which is typically characterized by a necrotic skin ulcer with extensive surrounding edema and regional lymphadenopathy. Bacillus anthracis, the causative agent, is a gram-positive, spore-forming rod; infections are quite rare in the United States. (Choice E) Trichinella, a roundworm transmitted by ingesting contaminated swine, is often associated with transient gastrointestinal symptoms followed by skeletal muscle pain, tenderness, swelling, and weakness. Educational objective: Bubonic plague is a zoonotic infection that causes febrile illness with regional inflammatory lymphadenopathy (buboes). The underlying pathogen is Yersinia pestis, a gram-negative coccobacillus that exhibits bipolar staining (resembling a closed safety pin). The major environmental reservoir is rodents, and transmission usually occurs via rodent flea bite. __________ References: Plague. (http://www.ncbi.nlm.nih.gov/pubmed/17416264)

A Previously Healthy 23-Year-Old Man Comes to the Office Due