Tularemia is an infection caused by the bacterium Francisella tularensis transmitted to humans from animals. Most often benign, it can cause complications in rare cases. Professor Christian Chuard, head of the infectiology department at the hospital in Fribourg, Switzerland, tells us more.
Definition: what is tularemia?
Tularemia is an infectious disease caused by the bacterium Francisella tularensis. It’s about a zoonosis – transmitted to humans by animals. Highly contagious, it has been on the list of notifiable diseases (MDO) since 2002 as part of the nuclear, radiological, biological and chemical risk prevention plan. Natural contaminations are therefore monitored by the health authorities, in order to detect malicious contaminations. “This bacterium is capable of infecting many animal species including, lagomorphs (hares, wild rabbits), suids (wild boars)domestic and wild carnivores, some species birds, wild rodents (field mice, voles, muskrats, coypu, etc.) as well as aquatic animals like crustaceans“, specifies thehandles. “Relatively common in the United States, Scandinavian countries, Russia and Japan, tularemia is on the rise in the rest of Europe“, notes theARS Auvergne-Rhône-Alpes. In 2018, according to the latest figures available from Public Health France, 133 cases of tularemia have been identified. And according to Pr. Christian Chuard, head of the infectiology department at the hospital in Fribourg, Switzerland, the number of cases of tularemia diagnosed in Switzerland has been “multiplied by ten in the last ten years“.”Some of the cases reported to public health authorities may be due to better detection of infections by doctors, who think about it more easily, rather than a true increase in incidence disease in the population“, notes the infectiologist.
How is tularemia transmitted?
“Currently the main reservoirs of bacteria are the rodents, rabbits and haresthe main vectors of the disease are ticksthe gateway being the tick bite“, explains Christian Chuard. “We have also been able to observe direct transmission from animals to humans, through blood, during the cutting of game, in particular“, he continues. Another mode of transmission: contamination by aerosolized particles. “You see this especially in the summer with farmers harvesting their fields. They are probably infected by the presence of dead animals or contaminated animal droppings“, adds the infectiologist. “The man becomes infected animal tank contact (skin inoculation, ingestion, aerosols), via arthropod vectors (bites/stings of ticks, more rarely mosquitoes or horseflies in certain regions) or from the environment (water, damp soil) where the bacteria can survive for several months“, summarizes the Francisella National Reference Centerin France.
What are the different forms of tularemia?
The Francisella National Reference Center distinguishes 6 forms of tularemia, which give different clinical signs depending on the entry point of the bacteria:
- ulcero-nodal and lymph node forms : this is the most common form, especially in Europe, via a tick bite.
- the oculo-nodal form
- the oropharyngeal form
- lung form
- the typhoid form
What are the symptoms of tularemia?
“Symptoms of tularemia may appear between 2 and 14 days after contamination, but most often 3 to 5 days after“, explains the ARS Auvergne-Rhône-Alpes. “For the nodal form, the most frequent, faced with a flu-like condition (fatigue, fever, headaches…), swelling of a ganglion (adenopathy) and a skin lesion at the site of the tick bite, the doctor should think about tularemia, especially if it is tick season, very active in summer, but more generally from March to October“, specifies Pr. Christian Chuard. The other specific symptoms according to the forms of tularemia are:
► For the oculo-nodal form: conjunctivitis with an enlarged gland in front of the ear after splashing into the eye
► For the oropharyngeal form: pharyngitis with a swollen gland in the neck area, sometimes digestive signs, after contamination by consumption of contaminated water or food
► For the pulmonary form: pleuropneumonia after contamination by inhalation or blood
► For the typhoid form: this is a generalized form of the disease accompanied by high fever and tuphos, a state of obsessive also found in typhus or typhoid fever, diseases to which it gave its name, regardless of the point of entry of the bacteria
The suspicion of tularemia is confirmed in two ways:
► The PCR test: “it is a local sample (tissue or secretion) which requires an open wound or a puncture of the lymph node. This is the most reliable test“, comments our expert.
► Serology : “Antibodies to the bacteria are then tested. However, the serology is generally positive only two to three weeks after contamination.
What are the complications of tularemia?
In the nodal form of tularemia, there are very few complications. “However, if left untreated, the lymph node, if located close to the skin, may spontaneously open outward and pour out its pus. Healing will then take quite a long time., explains Christian Chuard. For the pulmonary form, causing pneumonia, symptoms may be more severe in a frail person. For the typhoid form, the management is also much heavier. “In an immunocompromised person, it can cause very severe sepsis. But this form is really rare”says the doctor.
What is the mortality risk of tularemia?
According to the manual MSDmedical book known as the Merck Manual in the United States and Canada: “mortality is almost nil in treated cases and is nearly 6% in untreated cases ulcero-nodal tularemia. Mortality is higher in the form of type 1 infection (the disease encountered on the American continent) and in typhoid, septicaemic and pulmonary tularemia; it can go as far as 33% in untreated cases. Death is usually the result of massive infection, pneumonia, meningitis, or peritonitis. Relapses can occur in undertreated cases. Access confers immunityNote: this very severe form of tularemia is due to a subspecies of the bacterium Francisella tularensis which is not present in Europe. The subspecies, F. tularensis holarctica, active in Europe, is responsible for much less serious clinical forms.
What is the treatment for tularemia?
Specific treatments for tularemia are antibiotics of the class of quinolones and macrolides. Treatment usually lasts two to three weeks. “Note thatthe patient can be started on treatment without having been able to confirm the diagnosisbecause it is too early for serology or because the PCR test was considered too invasive“, concludes Prof. Chuard.
Thanks to Pr. Christian Chuard, head of the infectious diseases department at the hospital in Fribourg, Switzerland.