A bacterial zoonosis

Tularemia is a zoonosis caused by infection with Francisella tularensis.
Two subspecies are predominant:

• Francisella tularensis tularensis, which is highly virulent in North America;

• Francisella tularensis holarctica, found only in Europe and less virulent.

The bacterium survives for several weeks in the external environment (water, soil, carcasses), especially at low temperatures. The reservoir for the bacterium consists of wild small mammals (voles, field mice, etc.) and ticks (Ixodidae). The hare, frequently implicated in transmission to humans, is a species affected by the disease and is not a reservoir.

In this context, Santé publique France’s missions are:

• To ensure the epidemiological surveillance of tularemia within the framework of the system for notifiable diseases;

• To detect and investigate any unusual events or clusters of cases, and to support authorities in implementing control and prevention measures;

• To inform public authorities, healthcare professionals, and the general public.

Different routes of transmission

The reservoir of Francisella tularensis consists of wild small mammals (voles, field mice, etc.) and ticks (Ixodidae).
Hares and ticks are the main vectors of human tularemia. Domestic animals, such as sheep, cats, and dogs, are accidental hosts and rarely serve as a source of human infection.

Humans become infected:

• through direct skin contact (penetration of the pathogen through healthy skin is possible but facilitated by scratches or cuts) with infected animals, plants, soil, or contaminated materials (nails, blades, etc.), or through splashes into the eye (conjunctival entry point) or onto skin wounds;

• through tick bites, or more rarely, insect bites (mosquitoes, flies);

• through ingestion of contaminated food or water;

• through inhalation of contaminated aerosols in laboratories, inhalation of dust (feed, bedding), or wool contaminated by infected animals.

There are no documented cases of human-to-human transmission.

Several clinical forms

Regardless of the route of entry, tularemia begins suddenly after an incubation period of 3 to 5 days (ranging from 1 to 25 days).
Symptoms include fever, chills, weakness, joint and muscle pain, sore throat, headache, and sometimes nausea and vomiting.

The clinical forms of tularemia depend primarily on the route of entry:

• ulcerative-lymph node form (following direct skin contact): a local lesion at the site of bacterial entry, progressing to necrotic ulceration associated with regional lymphadenopathy that may suppurate, necrotize, and sclerose;

• lymph node form: regional lymphadenopathy without ulcers;

• ocular-ganglionic form (following ocular contact or splashing): conjunctivitis with regional lymphadenopathy;

• oropharyngeal form (following ingestion of contaminated food or water, or following inhalation of aerosols): stomatitis, pharyngitis, tonsillitis, cervical and retropharyngeal lymphadenopathy;

• pleuro-pulmonary form (primary following inhalation of a contaminated aerosol or secondary following dissemination): dry cough, bronchiolitis, pleuropneumonia, hilar lymphadenopathy, respiratory distress;

• “typhoid-like” or “septicemic” form: fever, headache, malaise, vomiting, diarrhea, abdominal pain; in the most severe cases: septic shock.

Tularemia usually has a favorable outcome (case fatality rate below 1% with the holarctica subspecies, but up to 30% in the absence of treatment with the tularensis subspecies).

Diagnosis

The diagnosis of tularemia can be confirmed biologically by the following tests:

• Serology: agglutination, ELISA, immunofluorescence. Antibodies appear around the 8th to 10th day, but their appearance may be delayed (up to 4–5 weeks) and they may persist for several years.

• Isolation of Francisella tularensis from samples of skin lesions or lymph node aspirates is possible only early in the disease and requires culture on specialized media.

• Gene amplification.

Francisella tularensis is a bacterium that must be handled in a biosafety level 3 laboratory. It is subject to regulations on microorganisms and toxins.

Preventive measures to reduce the risk of infection

Although tularemia is rare in France, it can be serious in humans. Populations at particularly high risk include anyone exposed to the droppings of small wild mammals, tick bites, and game: hunters, people working in forests, hikers, and residents of rural areas.
Preventive measures against the disease include wearing long-sleeved and long-legged clothing for recreational or professional activities in the forest, and checking the skin for ticks upon returning from outdoor activities. Additionally, it is recommended to avoid handling any dead animals found.

Hunters are a population particularly at risk for tularemia due to the skinning and gutting of game. Specific prevention measures for hunting and the culinary preparation of game may apply:

• avoid hunting animals that appear weak or sick for consumption;

• always wear waterproof gloves when skinning and gutting game; thoroughly clean the knife—while keeping the gloves on—and carefully wash your hands and forearms after these operations;

• in the event of an accidental injury during skinning, evisceration, or food preparation, the wound must be immediately cleaned with soap and water;

• Cook game meat thoroughly before eating it.