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Emergency and Acute Medicine: Tularemia
Tularemia is an acute febrile zoonotic illness caused by Francisella tularensis, a highly infectious, small aerobic gram-negative intracellular coccobacillus. It is notable for its extreme infectivity—very few organisms are required to cause disease—and lack of person-to-person transmission. Humans acquire infection through environmental exposure, including bites from infected ticks, deerflies, or mosquitoes; direct contact with infected animal tissue (especially rabbits); ingestion of contaminated food or water; or inhalation of aerosolized organisms (e.g., during lawn mowing or farming activities).
There are multiple subspecies of the organism, with Francisella tularensis subspecies tularensis (type A) being more virulent and common in North America, and Francisella tularensis subspecies holartica (type B) causing milder disease. Natural reservoirs include rabbits, rodents, and various wild and domestic animals, while vectors include ticks, biting flies, and mosquitoes. Due to its high virulence and ability to be aerosolized, tularemia has historically been studied as a potential biologic weapon.
Tularemia primarily affects individuals with outdoor exposure in endemic regions, such as farmers, hunters, forestry workers, and those handling animal carcasses. It is most common in the northern hemisphere and peaks during warmer months (June to October). Although relatively rare, it carries a mortality rate of 5–15% if untreated, which decreases to about 1% with appropriate therapy. Pediatric cases account for approximately 25% of infections.
Clinical presentation varies depending on the route of entry, with an incubation period typically of 3–5 days. The most common form is ulceroglandular tularemia, accounting for 70–80% of cases. It begins as a papule at the inoculation site that progresses to a painful ulcer, followed by regional lymphadenopathy and systemic symptoms such as fever, chills, headache, and myalgias. Glandular tularemia presents similarly but without a visible skin lesion. Oculoglandular tularemia occurs when the organism enters through the eye, causing conjunctivitis, chemosis, and regional lymphadenopathy. Pharyngeal tularemia results from ingestion of contaminated material and presents with severe exudative pharyngitis and lymphadenitis.
Pneumonic tularemia arises from inhalation and presents with fever, dry cough, pleuritic chest pain, and potentially severe pneumonia. Typhoidal tularemia is the most severe form, characterized by systemic illness without a clear entry site, often progressing to sepsis, multiorgan failure, and potentially death—particularly with type A strains.
Diagnosis is often challenging due to nonspecific laboratory findings and the absence of rapid diagnostic tests. Routine labs may be normal or show mild inflammatory changes. Blood cultures are often negative due to the organism’s fastidious growth requirements. Definitive diagnosis relies on serology, with antibody titers typically becoming diagnostic only after 10–14 days. Polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) are available in specialized laboratories. Imaging, such as chest radiography, may reveal pneumonia, pleural effusions, or hilar adenopathy in pulmonary cases.
Management in the emergency setting focuses on supportive care and early antibiotic therapy. Initial stabilization includes airway, breathing, and circulation (ABCs), oxygen supplementation for hypoxia, and intravenous fluids for dehydration or septic shock. First-line antimicrobial therapy consists of aminoglycosides, particularly gentamicin or streptomycin, administered for approximately 10 days. Alternative agents include ciprofloxacin or doxycycline, though these are bacteriostatic and associated with higher relapse rates. Importantly, β-lactam antibiotics and carbapenems are ineffective against F. tularensis.
Disposition depends on disease severity. Patients with severe illness, hemodynamic instability, hypoxemia, or typhoidal tularemia require ICU admission. Mild cases may be managed as outpatients with close follow-up and appropriate antibiotic therapy. Infectious disease consultation is recommended, particularly in severe or unclear cases.
Key clinical pearls include maintaining a high index of suspicion in patients presenting with fever and regional lymphadenopathy—especially when accompanied by a skin ulcer or conjunctivitis—and considering epidemiologic exposure history. Diagnosis is often delayed due to reliance on serology, and early empiric treatment is crucial. Tularemia remains a category A bioterrorism agent due to its high infectivity and potential for aerosol dissemination.
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