Brucellosis: antibodies to the causative agent of brucellosis in the blood

Normally, antibodies to the causative agent of brucellosis in the blood are absent. The diagnostic titer during the agglutination reaction is 1: 160 and higher.

The causative agents of brucellosis are brucellae, small immobile gram-negative bacteria. When diagnosing brucellosis, the obtained clinical and epidemiological data should be confirmed laboratory. For this purpose, bacteriological and serological methods of investigation are used. In acute brucellosis, a positive result of the study of hemoculture is obtained in 10-30% of cases (in 62-90%, if the causative agent is Brucella melitensis, in 5-15%, if - Brucella abortus ). The culture of CSF is positive in 45% of patients with meningitis. When blood, bone marrow, urine cultures are sown, the culture of brucella can be obtained in 5-10 days, and in some cases - in 20-30 days. In connection with this, serological methods have become widely used for diagnosis of brucellosis.

The most reliable serological test for the determination of antibodies to the causative agent of brucellosis in serum is the standard test tube assay (Wright's reaction), with it determine the content of antibodies reacting mainly with lipopolysaccharide antigens of brucella. An increase in antibody titres 4 times or more in serum samples obtained at 1-4 weeks intervals allows identifying the etiologic factor of the disease. In most patients, titres of specific antibodies increase on the 3-5th day from the onset of the disease. It is believed that the antibody titer is not less than 1: 160, followed by its growth. Elevated antibody titer was detected in 97% of patients in the first 3 weeks of the disease. The highest antibody titer is usually observed 1-2 months after the onset of the disease, in the future it begins to decline rapidly. Standard test tube agglutination test detects antibodies to the Bed and. abortus, Bed and. suis, Bed and. melitensis, but not to the Bed and. canis. Elevated antibody titers may persist in 5-7% of patients within 2 years after the infection. Therefore, Wright's reaction can not be used for differential diagnosis of brucellosis with other infectious diseases in the presence of a history of brucellosis within the last 2 years. The cause of false positive results can be a skin test for brucellosis, vaccination against cholera, as well as infections caused by cholera vibrio, Yersinia, Francisella tularensis. In some cases, false-negative results of the agglutination reaction in patients with brucellosis are possible, which is explained by the effect of the prozone, or the so-called blocking of antibodies. In chronic localized forms of brucellosis, titres may be negative or lower than 1: 160. Against the background of the treatment, IgG antibody titers are rapidly decreasing and approaching zero within a year. At relapse, the level of IgG antibodies again increases. The presence of a single increase in the IgG antibody titer of more than 1: 160 is a reliable objective indication of the current or recently transferred infection. After treatment and patient discharge from the hospital, serology is recommended for the first year after 1, 2, 3, 6, 9 and 12 months, and during the second year - quarterly.

RPHA is more sensitive and specific for the detection of brucellosis antibodies in the blood serum. Often, haemagglutinins are detected in cases where the agglutination reaction gives a negative or doubtful result.

RSK allows detecting complement-binding antibodies to brucella, appearing in the blood after agglutinins. The maximum antibody titers in the DSC are recorded by the 4th month of the disease, later their titer decreases, but in a small amount they are detected within 1 year. There are no significant advantages of RSK in comparison with the agglutination reaction.

[1], [2], [3], [4], [5]