How is anthrax diagnosed?

Diagnosis of cutaneous anthrax is based on characteristic local changes: the presence of a black scab with a rim of hyperemia ("black coal on a red background"), gelatinous painless edema and regional lymphadenitis, the appearance of general symptoms after the formation of a carbuncle. Of particular importance for diagnosis are epidemiological data (profession, livestock care, slaughter, cutting up carcasses, working with leather, skins, etc., wearing leather and fur products of non-factory tanning, eating meat that has not undergone veterinary and sanitary control, especially in case of forced slaughter of sick animals). In the generalized form of the disease, it is difficult to establish a diagnosis without epidemiological and laboratory data.

Etiological laboratory diagnostics of anthrax consists of:

• bacteriological studies, which take place in three stages: microscopy of smears from pathological material, isolation of a pure culture of the pathogen on nutrient media and study of its properties, biological testing on laboratory animals:
• detection of the pathogen's genetic material using the PCR method;
• serological studies:
• immunohistochemical studies;
• skin allergy test with anthraxin.

If cutaneous anthrax is suspected, the contents of the vesicles or carbuncles, ulcer discharge, sloughed off scabs and blood are taken for bacteriological examination.

If a generalized form is suspected, blood from the cubital vein, urine, vomit, feces, cerebrospinal fluid (if symptoms of meningitis are present), and sputum are taken for laboratory testing. During bacteriological testing, the pathogen is detected by bacterioscopy and fluorescent microscopy. In the material, bacteria are located in pairs or in chains surrounded by a common capsule. Spores are usually located in the center. The same substrates are used for sowing on nutrient media to isolate a pure culture of the pathogen, as well as for setting up a bioassay on laboratory animals.

Serological diagnostics of anthrax is based on the use of the fluorescent antibody method, RIGA (RPGA), and ELISA.

If cutaneous anthrax is suspected, a puncture biopsy of the skin in the center of the primary affect can be performed, followed by immunohistochemical examination of the obtained material or silver staining. Test systems have been developed to determine the genetic material of the anthrax pathogen using the PCR method. A skin-allergic test with anthraxin is used, which becomes positive in 82% of cases from the 3rd day of the disease. When studying livestock raw materials (skins, wool), the Ascoli thermoprecipitation reaction and other methods are used.

In the case of a generalized variant, an X-ray examination of the lungs is necessary. If the intestinal variant is suspected, an ultrasound of the abdominal organs is indicated, and in the case of clinical signs of meningitis, an ultrasound of the pulmonary system is indicated. Moderately expressed inflammatory changes and thrombocytopenia are detected in the blood, and signs of toxic nephrosis are detected in urine tests.

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Example of diagnosis formulation

A22.0. Anthrax, cutaneous form, severe course of the disease (a culture of B. anthracis was isolated from the discharge of the carbuncle).

Patients with a confirmed diagnosis or suspected anthrax are subject to emergency hospitalization in compliance with all transportation rules and sanitary and epidemiological regulations and isolation in boxes or separate wards.

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Differential diagnosis of anthrax

In the cutaneous form, differential diagnostics of anthrax is carried out with a furuncle, carbuncle, phlegmon, erysipelas, insect bites, and sometimes with the cutaneous form of tularemia and plague. Furuncles and carbuncles are characterized by sharp pain, the presence of pus under the crust, and the absence of widespread edema. In erysipelas, fever and intoxication precede local changes, characterized by sharp erythema on the skin, moderate pain, and a clear boundary between the affected area and healthy skin. With increased sensitivity to the poisons of some insects (wasp, hornet, bee, ant, etc.), hyperemia, sharp dense swelling with pain and a trace of the bite in the form of a dot in the center may appear at the site of the bite. Fever and intoxication are possible. All these symptoms develop within a few hours after a painful bite.

In the cutaneous form of tularemia, the primary affect (ulcer) is slightly painful. There is no infiltration or swelling of soft tissues, a regional bubo is detected. In plague, skin lesions are extremely painful, there are hemorrhages on the skin, and severe intoxication.

Differential diagnostics of generalized anthrax is carried out with sepsis, meningococcemia, pulmonary plague, lobar pneumonia, purulent meningitis, acute intestinal infections, peritonitis, intestinal obstruction. Without appropriate epidemiological and laboratory data, differential diagnostics presents great difficulties; often the diagnosis is established after death.

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