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How is tularemia diagnosed?
Last reviewed: 23.04.2024
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Diagnosis of tularemia is based on clinical, epidemiological and laboratory data.
In the general analysis of blood in the initial period, there is normocytosis or a small leukocytosis, an increase in ESR. The period of the height of the disease is characterized by leukopenia with lympho- or monocytosis. Neutrophilic leukocytosis is noted only when buboes are suppurated.
Specific diagnosis of tularemia is based on the use of serological and allergic tests, bacteriological examination and biological samples. The main serological methods are RA and RPHA with a diagnostic titer of 1: 100 and higher (diagnostic standard). The diagnostic value of RPHA is higher, as antibodies in a titer of 1: 100 are detected early, by the end of the first week (in the RA - from 10-15 days). To diagnose acute disease and determine postvaccinal titers, the study is conducted in dynamics in a week. If the antibody is not re-examined or their titer is not changed, the patient's blood is examined a third time a week after the second examination. Increasing the antibody titer by 2-4 times in RA and RPHA confirms the diagnosis of tularemia. The absence of growth indicates the anamnestic character of the reaction. Other serological methods of diagnosing tularemia have been developed: RPGA, ELISA. ELISA on solid-phase carrier is positive from 6-10 days of the disease (diagnostic titer 1: 400); by sensitivity, it is 10-20 times higher than other methods of serodiagnostics.
Diagnosis of tularemia can be performed using a skin allergic test, which is characterized by strict specificity. It is referred to as early diagnostic methods, since it becomes positive already from the 3rd-5th day of the disease. Tularin is injected intradermally or dermally (in strict accordance with the instructions used) in the middle third of the palmar surface of the forearm. The result is taken into account at 24.48 and 72 hours. The sample is considered positive with a diameter of infiltration and hyperemia of at least 0.5 cm. One hyperemia that disappears after 24 hours is regarded as a negative result. The sample with tularin does not allow to distinguish between fresh cases of anamnesis and anamnestic and grafting reactions. When there are contraindications to the use of skin test (increased sensitization), resort to the method of allergodiagnostics in vitro - the reaction of leukocytolysis.
Auxiliary role is played by bacteriological methods and biological test, which can be carried out only in specially equipped laboratories that have permission to work with the pathogen of tularemia.
PCR, with which it is possible to detect specific DNA in various biological substrates, is positive in the initial febrile period of the disease, therefore it is considered a valuable method of early diagnosis of tularemia.
[Differential diagnosis of tularemia
Differential diagnosis 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.
The plague is characterized by a more pronounced intoxication. Plague bubon is characterized by sharp soreness, tightness, fuzziness of contours, periadenitis, skin hyperemia, increased local temperature. The plague bubo dissolves rarely, but is suppressed and opened earlier than with tularemia (respectively, after 1 and 3 weeks). The predominant localization of the bubo in the plague is the area of the inguinal and femoral lymph nodes (they are less often affected in tularemia). Ulcer with tularemia less painful than with plague, or generally painless. With a plague, there are often terrible complications and an unfavorable outcome.
Tularemia pneumonia from the plague differs from the absence of bloody sputum (with rare exceptions). Patients with tularemia are not contagious. It should be borne in mind that the areas of distribution of plague and tularemia do not coincide.
Nonspecific lymphadenitis (staphylococcal and streptococcal) is often accompanied by lymphangitis and periadenitis. They are characterized by severe soreness and hyperemia of the skin, early suppuration (compared with tularemia). Their appearance is usually preceded by a primary purulent focus in the form of panaritium, furuncle, carbuncle, infected wound, rubbing, etc. Fever and symptoms of intoxication are more often absent or occur later than lymphadenitis. In the hemogram, unlike tularemia, neutrophilic leukocytosis and an increase in ESR are recorded.
Differential diagnosis of tularemia of the anginous-bubonic form is carried out with usual angina. Tularemia is characterized by unilateral tonsillitis; raids on the tonsils resemble those in diphtheria: after their rejection, they detect an ulcer. The regional (submandibular) lymph nodes are enlarged significantly, but they are practically painless on palpation. Sore throat is less intense than with angina, and occurs later (after 2-3 days).
In contrast to diphtheria, angina with tularemia is characterized by a more acute onset, usually one-sided localization and rarely spreading outside the tonsils with plaque. The results of laboratory research are of decisive importance.
With tuberculous lymphadenitis, the disease begins gradually, with subfebrile temperature. Lymph nodes are dense, painless, smaller in size than with tularemia.
Ulcers on the skin with tularemia differ from the anthrax painfulness, smaller size, absence of black scab and swelling of the surrounding tissues.
Tularemia pneumonia differs from croupous less stormy start, more moderate toxemia and sluggish course.
For benign lymphoreticulosis (felinosis). As well as for tularemia, is characterized by the presence of primary affect in the area of the infection gate and bubo (most often in the axillary and ulnar lymph nodes). Most important is the indication of contact with the cat (90-95% of patients) in the form of a scratch or a bite. The course of the disease is benign, intoxication is not expressed.