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How is tularemia diagnosed?
Last reviewed: 03.07.2025
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Diagnosis of tularemia is based on clinical, epidemiological and laboratory data.
In the general blood test in the initial period, normocytosis or slight leukocytosis, an increase in ESR are detected. The period of the peak of the disease is characterized by leukopenia with lymphocytosis or monocytosis. Neutrophilic leukocytosis is noted only with suppuration of buboes.
Specific diagnostics of tularemia is based on the use of serological and allergic tests, bacteriological examination and biological tests. The main serological methods are RA and RPGA with a diagnostic titer of 1:100 and higher (diagnostic standard). The diagnostic value of RPGA is higher, since antibodies in a titer of 1:100 are detected early, by the end of the first week (in RA - from the 10th to 15th day). To diagnose an acute disease and determine post-vaccination titers, the study is carried out dynamically after a week. If antibodies are not detected during a repeated study or their titer does not change, then the patient's blood is examined for the third time a week after the second examination. An increase in the antibody titer by 2-4 times in RA and RPGA confirms the diagnosis of tularemia. The absence of growth indicates an anamnestic nature of the reaction. Other serological methods for diagnosing tularemia have also been developed: RPGA, ELISA. ELISA on a solid-phase carrier is positive from the 6th to 10th day of the disease (diagnostic titer 1:400); in terms of sensitivity, it is 10-20 times higher than other serodiagnostic methods.
Tularemia can be diagnosed using a skin allergy test, which is highly specific. It is considered an early diagnostic method, as it becomes positive as early as the 3rd to 5th day of the disease. Tularin is injected intradermally or superficially (in strict accordance with the instructions) into the middle third of the palmar surface of the forearm. The result is recorded after 24.48 and 72 hours. The test is considered positive with an infiltrate and hyperemia diameter of at least 0.5 cm. Hyperemia alone, which disappears after 24 hours, is considered a negative result. The tularin test does not distinguish fresh cases of the disease from anamnestic and vaccination reactions. When there are contraindications to the use of a skin test (increased sensitization), they resort to the in vitro allergy diagnostics method - the leukocytolysis reaction.
An auxiliary role is played by bacteriological methods and biological testing, which can only be carried out in specially equipped laboratories that have permission to work with the causative agent of tularemia.
PCR, which can detect specific DNA in various biological substrates, is positive in the initial febrile period of the disease, so it is considered a valuable method for the early diagnosis of tularemia.
[ Differential diagnosis of tularemia
Differential diagnostics of tularemia in the initial period of the disease is carried out with influenza, typhoid and typhus, pneumonia, and subsequently - plague, anthrax, ulcerative necrotic tonsillitis, diphtheria, nonspecific lymphadenitis, tuberculosis, sepsis, malaria, brucellosis, mumps, benign lymphoreticulosis, infectious mononucleosis.
Plague is characterized by more pronounced intoxication. Plague bubo is characterized by sharp pain, density, blurred contours, periadenitis, hyperemia of the skin, and an increase in local temperature. Plague bubo rarely resolves, and suppurates and opens earlier than with tularemia (respectively, after 1 and 3 weeks). The predominant localization of the bubo in plague is the area of the inguinal and femoral lymph nodes (with tularemia, they are affected less often). The ulcer in tularemia is less painful than in plague, or even painless. With plague, severe complications and an unfavorable outcome occur more often.
Tularemia pneumonia differs from plague pneumonia by the absence of bloody sputum (with rare exceptions). Patients with tularemia are not contagious. It should be taken into account that the areas of distribution of plague and tularemia do not coincide.
Non-specific lymphadenitis (staphylococcal and streptococcal) is often accompanied by lymphangitis and periadenitis. They are characterized by severe pain and hyperemia of the skin, early suppuration (compared to tularemia). Their occurrence is usually preceded by a primary purulent focus in the form of a panaritium, furuncle, carbuncle, infected wound, abrasion, etc. Fever and symptoms of intoxication are often absent or occur later than lymphadenitis. In the hemogram, unlike tularemia, neutrophilic leukocytosis and an increase in ESR are recorded.
Differential diagnostics of tularemia of the angina-bubonic form is carried out with common tonsillitis. Tularemia is characterized by unilateral tonsillitis; plaque on the tonsils resembles that of diphtheria: after their rejection, an ulcer is found. Regional (submandibular) lymph nodes are significantly enlarged, but they are practically painless upon palpation. Sore throat is less intense than with tonsillitis, and occurs later (after 2-3 days).
Unlike diphtheria, angina in tularemia is characterized by a more acute onset, usually unilateral localization and plaques that rarely spread beyond the tonsils. The results of laboratory tests are of decisive importance.
In tuberculous lymphadenitis, the disease begins gradually, with a subfebrile temperature. The lymph nodes are dense, painless, and smaller in size than in tularemia.
Skin ulcers caused by tularemia differ from anthrax ulcers in that they are more painful, smaller in size, and lack a black scab and swelling of the surrounding tissues.
Tularemia pneumonia differs from lobar pneumonia in its less violent onset, more moderate toxicosis and sluggish course.
For benign lymphoreticulosis (felinosis), as well as for tularemia, the presence of a primary affect in the area of the infection gate and bubo (usually in the area of the axillary and elbow lymph nodes) is characteristic. The most important indication is contact with a cat (90-95% of patients) in the form of a scratch or bite. The course of the disease is benign, intoxication is not expressed.