Brucellacapt®

Brucellacapt®


Brucellacapt® uses the Brucella abortus strain although, serologically, there is no difference between Brucella abortus, Brucella melitensis and Brucella suis. According to the Manual of Diagnostic Tests and Vaccines for Terrestrial Animals from the OIE (http://www.oie.int/eng/normes/mmanual/A_00052.htm): "It should be emphasised that antigen made with one of these B. abortus strains is also used to test for B. melitensis or B. suis infection. According to the Manual of Clinical Microbiology, 8th ed from the ASM: "The standard SAT method uses killed whole-cell B. abortus antigen and detects antibodies against B. abortus, B. suis and B. melitensis but not B. canis."

According to WHO, the only way to distinguish between B. abortus and B. melitens is through bacteriological culture (isolation of the bacteria from samples). Brucellacapt®, like the other current serological methods (ELISA, Rose Bengal, SAT), will not discriminate between Brucella abortus, Brucella melitensis or any of the strains that contain LPS, which is common to all species of Brucella.

Although treatment of the disease is not Vircell’s field of expertise, scientific literature supports that the treatment for both infections is the same (both are sensitive to the same antibiotics) with the exception of some rare strains such as B. melitensis strain REV-1.Therefore, differentiation is only relevant from the epidemiological point of view only. Using Brucellacapt® offers the additional advantage (compared ELISA, SAT, Rose Bengal etc…) that it allows for monitoring the evolution of the patient during their treatment, and it allows the early detection of reinfections and chronic phases of the illness. In any case please refer to the recommendations published by the WHO for diagnosis and treatment of brucellosis, for more specific information.

As with Rose Bengal, the acidic medium used in the reaction avoids the prozone phenomenon. Prozone in Brucellacapt® is extremely rare. Sometimes we have found it in very positive sera, but only in the first dilution at 1/40, and never at titers higher than that. With the dilution that we propose for screening there should never be prozone, if the technique is performed correctly. In the case of titration, the first dilution will show negative, and the rest of dilutions will be positive. But again, this is rare, and more commonly found in other techniques such as normal agglutination

Brucellacapt® can be used in two ways: in titration (24 tests), or in screening (96 tests). Both procedures are explained in the package insert. The kit includes enough diluent to perform titration. To use it in screening mode, additional serum diluent will be required (Ref. B0002). This can be acquired separately through your local distributor. In both cases, it is highly recommended to use of a humid chamber during incubation time, so as to avoid desiccation of the sample. Vircell can provide you with humid chambers, free of charge, on request.

Brucellacapt® can be used for detection of acute brucellosis. Its sensitivity and specificity in both acute and chronic cases has been reflected in scientific literature. However, in prevalent areas where many patients are tested every year, there are more economic methods for easy detection of acute cases (Rose Bengal, ELISA…) The application of Brucellacapt® in endemic areas becomes relevant for detection of chronic cases, as none of the above methods is sensitive enough for adequate diagnosis of focalised forms of brucellosis.
The three methods, Rose Bengal, ELISA and Brucellacapt®, would be equally accurate in detecting the acute cases. Rose Bengal would show false negative results in the chronic and past infection samples (approximately 75% of chronic cases would be missed). ELISA and Brucellacapt® would detect all chronic samples and past infections. ELISA however is unable to distinguish between them. Using Brucellacapt, titers above 1/320 are indicative of chronic infection, allowing for the application of an adequate treatment to chronic sick patients.
The test is not intended for identification of IgA, or IgG parameters. Brucellacapt® is a quantitative test that allows the detection of non agglutinating antibodies, and their quantification through adequate titration. It allows a better correlation with the diagnosis of chronic stages of brucellosis.
This will depend on the prevalence of the disease among the population in a particular country. In a low prevalence area, detection of acute brucellosis can be done by either IgG or IgM, since the presence of any of them is a significant marker of infection.

The SAT test refers to Wright’s Serum Agglutination Test. Rose Bengal is a rapid agglutination test. Also, the acidic medium in which Rose Bengal is performed makes it more sensitive and specific in comparison to SAT.

So far, there are no studies comparing these tests, because Rose Bengal is a qualitative test, while Brucellacapt® is quantitative. It should be kept in mind that the application of both tests is different. Rose Bengal is indicated for suspected acute cases of brucellosis, Brucellacapt® for chronic cases.
Although widely used in all countries nowadays, Brucellacapt® was designed in its origin for detection of chronic cases in areas of high prevalence. The cut-off dilution for Brucellacapt® is based on clinical evidence and seroprevalence data of the illness in endemic areas of the disease, and established during the course of several published studies, which are available on our website. Laboratories in endemic countries screen samples at 1/320 and 1/640, as in those areas lower titers are seldom considered significant.
The correct way to establish the limit titer is to compare samples from patients with samples from healthy population, and carry out a ROC analysis. In an area of low prevalence of the disease a 1/320 cut off for the screening assay seems too high, and in such circumstances, a complete titration would be advisable. The screening procedure detailed in the brochure was designed for specific circumstances, but there would be no technical inconvenience in carrying out the screening procedures at different titers, whenever the calculations to achieve the final titers used are carried out carefully. For instance, in a country like Germany, a screening dilution of 1/80 1/160 would be adequate.

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