DESCRIPTION

• Tularemia is an infection caused by the gram-negative bacterium, Francisella tularensis. Presenting symptoms include fever, myalgia, and headache 3 to 5 days (ranging from 1 to 21 days) after initial exposure. The extent of the illness depends on infecting dose, subspecies, and route of entry.
• Six clinical forms are typically described:
  • Ulceroglandular tularemia
    • Constitutes 75% of all cases
    • Begins with a papule at the site of entry which ruptures and ulcerates
    • Painful local and regional adenopathy ensues
  • Glandular tularemia
    • Identical to the ulceroglandular form however does not have an identified primary skin lesion
  • Oculoglandular tularemia
    • Occurs when the organism gains access via the conjunctival sac
    • Usually from the patient rubbing the eyes with contaminated fingers
    • Yellow nodules and ulcers may appear on the palpebral conjunctiva associated with enlarged preauricular nodes.
  • Oropharyngeal tularemia
    • Occurs after the ingestion of contaminated food or water
    • An ulcerative or membranous tonsillitis accompanies a painful sore throat
    • Lower GI tract involvement with vomiting, diarrhea, and abdominal pain may occur.
  • Typhoidal tularemia
    • Presents with fever of unknown origin, without localizing lymphadenopathy or skin findings
    • Shock, pleuropulmonary findings, odynophagia, diarrhea, and bowel necrosis are often associated.
  • Pneumonic tularemia
    • Occurs after inhalation of the organism and is the most fulminant and lethal form
    • Can also be associated with ulceroglandular and typhoidal tularemia
    • Symptoms include fever, dry cough, and pleuritic chest pain.
    • Tularemia in this form is a feared potential biologic weapon because an exposure to only 1 to 10 colony-forming units can result in infection.
• F. tularensis is currently listed as a class A bioterrorism agent because of its potential ease for dissemination and infection as well as potential for high case fatality rates.

EPIDEMIOLOGY

• F. tularensis is found primarily in the Northern hemisphere from the 30 to 70 degree latitudes. Wild and domestic mammals (e.g., cats, dogs, rabbits, hares, squirrels, boars, beavers, deer, rodents) may be infected as well as invertebrate vectors (e.g., ticks, deerflies, horseflies, mosquitoes).
• Humans acquire tularemia after a bite by an infected arthropod or through direct contact with tissues or body fluids of an infected animal. The subspecies holarctica has been shown to persist in various water sources, and waterborne transmission to humans has been reported.
• Inhalational exposure can happen in the laboratory setting or after the organism is aerosolized during meat preparation or certain outdoor activities.
• Frequently reported during the summer months in children between 5 and 9 years of age and adults >55 years old with a male preponderance
• Approximately 200 cases are reported each year in the United States with the highest number of cases occurring in the south central states (Arkansas, Wyoming, Nebraska, Kansas, South Dakota, Colorado, Oklahoma, Missouri, and Kentucky).

ETIOLOGY

Tularemia is caused by a small, fastidious, nonmotile, gram-negative coccobacillus; four distinct subspecies have been described:

• Tularensis (type A): found primarily in North America; causes the most severe disease
• Holarctica (type B): found primarily in Europe and Asia; less virulent than tularensis
• Novicida: rarely isolated but can be found worldwide
• Mediasiatica: recovered from ticks and animals in Central Asia; not associated with disease in immune-competent humans
• An additional species, Francisella philomiragia (formerly Yersinia philomiragia), has also been reported. This is a rare cause of human disease and is possibly associated with saltwater exposure.

RISK FACTORS

• Most frequently infected groups include hunters, trappers, farmers, and veterinarians who engage in activities involving close contact with wild animals or exposure to various arthropod vectors.
• Tick exposure is a common mode of transmission in children in the United States.
• Infection has also been linked to landscapers using lawn mowers and brush cutters.
• Laboratory personnel who is handling samples that are potentially infected with F. tularensis

GENERAL PREVENTION

• Isolation of the hospitalized patient
  • Standard precautions are recommended for protection against secretions. Human-to-human transmission has not been reported in the health care setting.
• Control measures
  • Protective clothing and insect repellent should be used to minimize insect bites.
  • Routine inspection and immediate removal of ticks after outdoor activity in endemic areas
  • Rubber gloves should be worn while handling or cooking wild animals (e.g., rabbits, lemmings) that are possibly contaminated with F. tularensis.
  • Game meat should be cooked thoroughly.
  • Avoid drinking from outdoor water sources that may have contaminated water.
  • Laboratory workers should wear rubber gloves and masks in a biosafety level 3 facility when handling specimens that contain F. tularensis.
• Vaccine
  • There is no available vaccine to protect against F. tularensis.

PATHOPHYSIOLOGY

• Human infection can result from various modes of entry:
  • Skin contact with infected animals
  • Vector-borne transmission after the bite of a tick (dog tick, wood tick, lone star tick), mosquito, horsefly, or deerfly
  • Inhalation of aerosolized organisms during crop harvesting, disturbance of contaminated hay, grass cutting, and by laboratory workers
  • Ingestion of contaminated food products or water
• A primary lesion develops at the site of exposure, followed by local and regional lymph node swelling and tenderness.
• After skin inoculation or inhalation, the organism can spread via the bloodstream to various organs.