Tularemia

Last revised by Andrew Murphy on 09 Apr 2022

Tularemia is a rare and highly virulent febrile zoonotic bacterial infection caused by Francisella tularensis, which has been developed as a bioweapon by several countries. It can infect the skin and mucous membranes, lungs and intestine and cause systemic disease and death. Tularemia is a notifiable disease.

The most virulent form, Francisella tularensis biovar tularensis can cause fatal pneumonia and occurs mainly in Canada and western and central southern North America where around 200 cases are reported each year. Less virulent subspecies predominate in continental Europe and Asia 1. Animal hosts include mammals, birds, amphibians, reptiles and arthropods 1. Infection can occur by direct contact with a living or dead animal carrier, contaminated water, mud, hay or straw, through an insect bite or from a laboratory plate. No human to human transmission has been documented. Bacteria are hardy and can survive for weeks even in frosty environments but are destroyed by adequate cooking. The term ‘lawnmower disease’ refers to the infection caused by the spattering of animal carcass fragments. Just 10 - 50 organisms are sufficient to cause infection.

Serological detection of antibodies by ELISA, PCR, or indirect fluorescent antibody testing of suppurative material. Warn laboratory staff as handling precautions are necessary.

Infection takes different forms depending on the route of infection:

  • skin lesion or ulcer with regional lymphadenopathy
  • oropharyngeal disease
  • eye disease
  • pneumonic disease through inhalation of an aerosol
  • intestinal disease through ingestion of inadequately cooked meat or contaminated water
  • systemic typhoidal disease
  • septic shock and multi-organ failure

Subjects can be asymptomatic or present with non-specific symptoms such as fever, chills, headache, arthralgia, myalgia, weakness, dry cough, hemoptysis or diarrhea.

If untreated tularemia can cause the following:

Francisella tularensis is an aerobic Gram-negative coccobacillus with surface pili that enable it to bind to host cells. Macrophages phagocytose the bacteria. The bacteria then inhibit normal phagosome function and lyse the phagosome membrane, erupting into the cytoplasm where they breed, killing the host cell which subsequently bursts, releasing the progeny. Infected foci become necrotic, producing caseating granulomata which may contain multi-nucleated giant cells. Abscesses can form.

Patchy multifocal consolidation is frequently accompanied by pleural effusion and marked hilar and mediastinal lymphadenopathy. Alternatively, pulmonary nodules or masslike consolidations form which can mimic lung cancer. Resolution is slow, taking up to three months.

Streptomycin is the drug of choice. Tetracyclines and fluoroquinolones can be effective.

The bacterium was discovered in California in 1911 and was named after Edward Francis (1872-1957), a physician and researcher who led the investigation into tularemia, discovering the link in 1921. All six investigators contracted the disease despite elaborate precautions.

  • mucosal and skin disease is uncommon and mostly associated with rural occupations and hobbies
  • ​pneumonitis and systemic disease are rare and often fatal
  • tularemia is resistant to the usual antibiotics, streptomycin being the drug of choice
  • strict precautions can prevent disease transmission in the laboratory
  • in the event of a bioterrorism attack, aerosol inhalation would affect many people causing serious illness and many deaths

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