Diagnosis
Indications for Testing
A history of contact with rabbits, ticks, dogs, cats, or skunks along with nonspecific febrile illness with prominent lymphadenopathy
- Negative history of animal contact does not rule out diagnosis
Laboratory Testing
- CDC diagnostic testing for tularemia
- Serology – acute and convalescent phase titers
- Preferred means of confirmation; retrospective in nature
- Fourfold increase between acute and convalescent serology or >1:160 on acute titer
- Cross-reactivity between Brucella, Salmonella, Yersinia, and Legionella antigens
- Culture – frequently negative
- Difficult to culture – fastidious organism
- Select agents – confirmed positive culture requires approval before transfer
- PCR – not widely available but very sensitive
- Consider testing for other disorders such as Rickettsia rickettsii (Rocky Mountain spotted fever), Rickettsia typhi (typhus fever), Brucella spp, and Pasteurella multocida (pasteurellosis)
Imaging Studies
Chest x-ray for patients presenting with signs and symptoms of pneumonia – demonstrates infiltrates
Differential Diagnosis
Background
Epidemiology
- Incidence – <1/100,000 in U.S.
- Most cases occur in the west-central and mountain regions – 56% of total cases from 1990-2000 occurred in Arkansas, Oklahoma, Missouri, and South Dakota
- Transmission – blood-sucking arthropods, contact with infected animals via inapparent abrasions, consumption of contaminated water, airborne spread of contaminated materials
- Primarily a disease of wild animals, especially rabbits
- Risk groups – farmers, veterinarians, hunters, landscapers, meat handlers, lab workers
- In U.S., human vectors are primarily ticks and deer flies
- Tick vectors include Amblyomma americanum, Dermacentor andersoni, Dermacentor variabilis
- Peak seasons – spring and summer
- Historical peaks during fall and early winter (hunting season)
Organism
Gram-negative, aerobic, nonspore forming, fastidious coccobacillus
- Two main biovars are F. tularensis subsp. tularensis (type A) and F. tularensis subsp. holarctica (formerly subsp. palearctica, type B)
- Type A found predominantly in U.S.
- Type B found predominantly in Europe and Asia
- F. tularensis subsp. novicida (type C) – low-virulence strain in North America
Clinical Presentation
- Average incubation – 3-5 days (range 1-21 days)
- Disease often begins with the sudden onset of flu-like symptoms, including chills, fever, headache, generalized aches
- Forms of tularemia (mostly depends on portal of entry)
- Ulceroglandular
- Most common form in adults
- Direct contact with animal or insect bite
- Starts as small, painful papule that becomes an ulcer at entry portal with associated lymphadenopathy
- Glandular – similar presentation to ulceroglandular but lacking ulcer
- Most common form in children
- Progresses to fever, chills, myalgia, possibly septicemia
- Oculoglandular – Parinaud syndrome
- Conjunctival entry via contaminated fingers, splashes, aerosols
- Unilateral intense conjunctivitis, preauricular, submandibular, cervical lymphadenopathy
- Sequelae of corneal perforation and iris prolapse
- Oropharyngeal and gastrointestinal
- Ingestion of contaminated food or water
- Oral – exudative pharyngitis; deep, cervical lymphadenopathy
- Gastrointestinal – ulcerative gastrointestinal lesions, diarrhea
- Pneumonic
- Inhalational exposure or extension from systemic disease (typically ulceroglandular form)
- Pneumonia with dry cough and pleuritic chest pain
- Often occupational exposure (sheep shearing, animal husbandry, farming, lawn/brush cutting, laboratory workers)
- Typhoidal
- Rare in U.S.
- May occur from any portal of entry
- Usually associated with bacterial gastrointestinal or pneumonic disease and consumption of poorly cooked wild game
- High fever, headache, diarrhea, sore throat, anorexia
- Complications – septicemia, meningitis, endocarditis, hepatitis, renal failure
