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Causes and pathogenesis of tularemia
Last reviewed: 04.07.2025
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Causes of tularemia
The causative agent of tularemia, Francisella tularensis, is a small (0.2-0.5 µm) non-motile gram-negative rod that grows well under aerobic conditions in nutrient media with the addition of cysteine, glucose and blood products.
Pathogenesis of tularemia
The pathogen enters the body through the skin or mucous membranes of the eyes, respiratory tract, gastrointestinal tract. At the site of pathogen introduction, a primary affect often occurs in the form of an ulcerative-necrotic defect and regional lymphadenitis. When the lymphatic barrier is broken, the pathogen and its toxins enter the blood, which marks the occurrence of bacteremia and generalization of the process, as a result of which metastasis of the infection is possible with the formation of secondary tularemia buboes and damage to internal organs.
Epidemiology
Tularemia is a typical natural focal zoonotic infection. In natural foci, the main source of infection is rodents: water rats and mice. Infection of many domestic animals, as well as various parasitic ticks and insects, has been established. A sick person does not play a role as a source of infection in tularemia.
The transmission of infection among animals is carried out mainly by blood-sucking arthropods: ticks, mosquitoes, fleas, etc. Routes of infection for humans:
- contact - through contact with sick or dead animals, with environmental objects contaminated with rodent excrement;
- alimentary - when consuming food and water contaminated with excrements of infected rodents;
- airborne - when inhaling infected dust;
- transmission - from bites of ticks, mosquitoes, horseflies, midges, etc. Children are usually infected by transmission and alimentary routes. Disease
They are encountered almost exclusively in rural areas, with isolated cases recorded on the outskirts of cities, close to the swamp foci of tularemia. In urban conditions, children can become ill through contact with domestic animals, especially with the corpses of dead rodents, as well as when traveling with their parents outside the city. Sporadic cases are usually noted, but epidemic outbreaks are also possible among children in pioneer camps, close to natural foci of infection. Susceptibility to tularemia is apparently universal. Those who have recovered from the disease develop a strong immunity lasting at least 10-15 years.
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