Tularemia
Dima Youssef
James W. Myers
INTRODUCTION
Tularemia is a zoonotic disease caused by Francisella tularensis.
There are three subspecies of F. tularensis.
Tularensis (type A), which is the most common type in North America and is highly virulent in humans and animals
Holarctica (type B), a less virulent type, responsible for human tularemia infection in Europe, Asia, and North America
Mediasiatica, also less virulent and found in Asia
Francisella philomiragia and Francisella novicida are closely related species that are found in immunocompromised patients.
F. tularensis is a small, facultatively intracellular, gram-negative coccobacillus.
EPIDEMIOLOGY
Small mammals such as voles, mice, squirrels, and rabbits that are reservoirs for F. tularensis acquire tularemia through bites from ticks, fleas, and mosquitoes and also through contact with contaminated environments.
Survives for weeks in water, moist soil, or animal carcasses
Human infection
Tick bites from hard tick species
Femoral-inguinal node involvement
Dog tick, Dermacentor variabilis
The lone star tick, Amblyomma americanum
Rocky Mountain wood tick, Dermacentor andersoni
Deer flies
Cat bites
Contact with infected animal tissues or fluids
Contact with or ingestion of contaminated water, food, or soil
Inhalation of bacteria
Midwestern states usually have the highest incidence.
The highest incidence is in 5- to 9-year-olds and 75- to 79-year-olds.
Males
Summer months
Mortality rate around 10% overall
CLINICAL
2 to 5 days (up to 2 weeks) incubation period
Fever, chills, cough, nausea, and other nonspecific symptoms predominate early.
Symptoms can last for days to months without treatment.
TYPES OF TULAREMIA
Ulceroglandular (45% to 85% of cases. All others are 5% to 15%)
Fever
The painful papule progresses to a vesicle, then a pustule and finally to an ulcer over several days in most patients
The ulcer is painful and may be associated with painful lymphadenitis. Make take several weeks to heal. May appear sporotrichoid.
Sinus tracts can form.
Scab formation
Glandular tularemia
Lymphadenopathy without a skin lesion
Skin lesion may have been there but disappeared.
May persist for a long time and even suppurate
Often related to arthropod exposure
Oculoglandular tularemia (Parinaud syndrome)
Portal of injury is from the conjunctiva, either from the patient’s fingers or from splashes into the eye.
Usually but not always unilateral
Usually no loss of vision
Lid edema
A painful conjunctivitis, with occasional ulceration
Painful lymphadenopathy
Cervical
Preauricular
Submandibular
Oropharyngeal tularemia
Eating poorly cooked game
Ingestion of contaminated water or food
Exudative pharyngitis or tonsillitis
Ulceration, stomatitis
Often, these patients have tender cervical lymph nodes that may suppurate and be complicated by fistula formation.
Previous, large outbreak in war-torn Kosovo reported
Pneumonic tularemia
May be primary if the patient inhales infective dust. Often occupation related
Usually arises weeks to months after other forms of tularemia, especially typhoidal and ulceroglandular
Fever
Dry cough
Chest pain
Dyspnea
Hemoptysis
Abnormal radiographs
Subsegmental or lobar infiltrates
Hilar adenopathy
Less common manifestations are air space opacification of an entire lobe or segment, cavitation, oval opacities, pericardial effusion, linear opacities and septal lines,
apical and miliary disease resembling tuberculosis, a mediastinal mass, empyema with bronchopleural fistula, and residual cystic changes, calcification, and fibrosis.
Pleural effusions (30% of cases) mimic TB.
High pleural fluid concentrations of adenosine deaminase, lysozyme, and beta 2-microglobulin occur in both diseases.
As is the case with tuberculous pleural effusions, pleural fluid in tularemia may show an abundance of lymphocytes, predominantly CD4-positive T lymphocytes.Related posts:
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