brucellosis examination, brucellosis diagnosis
- 2021-10-19 12:56:07
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Common tests for brucellosis
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1. Complete blood count
Mainly detect white blood cell count, lymphocyte count, red blood cell sedimentation rate. The white blood cell count is normal or low. Relative or absolute increase in lymphocytes. Sometimes there may be a small number of atypical lymphocytes. The erythrocyte sedimentation rate increases in the acute phase, but is normal or high in the chronic phase, and the continuous increase speed indicates activity.
2. Pathogen isolation
It can be separated from blood, bone marrow, cerebrospinal fluid, urine, pus, etc. The positive rate of early blood and bone marrow culture can reach 70% to 80%. The positive rate of bone marrow culture is higher than that of blood culture. Brucella bovis is not easy to grow when it is first isolated and requires a proper carbon dioxide environment. Innbruella grows slowly, so various cultures need to be incubated for 2 to 4 weeks and there is no bacterial growth before it can be judged as negative. However, it has been reported that if the BACTEC9240 blood culture system is used, 93% (90/97) can be detected within 5 days or 97.6% (41/42) can be detected within 2-6 days. Recent reports have also confirmed this: blood cultures can all be within 7 days, and bone marrow cultures can get positive results within 4 days. It is generally believed that the positive rate of blood culture is high in the acute phase and low in the chronic phase. If necessary, the specimen can be inoculated with guinea pigs to isolate Brucella. Someone suggested that the specimens, especially blood from chronic brucellosis, should be injected into the yolk of the egg, incubated at 37°C for 5 days, and then transferred to the agar slant, and observed at 37°C for 2 to 3 days. Positive rate. The bacteria obtained from cerebrospinal fluid, urine, pus, etc. can be cultured in guinea pigs or mice.
3. Immunological examination
(1) Serum agglutination test:
There are many methods. Common ones include test tube method and flat plate method. The former is more sensitive, simpler to operate, and has better specificity, so this method is commonly used in laboratories; the latter is simpler to operate and has high sensitivity, but may have false positives, so it is suitable for screening tests. The plate method is divided into many kinds, among which the Tiger Red Buffer Slide Agglutination Test (RBPT) is the most effective. The agglutination test should be measured month by week, and the high titer or the multiplication of the titer has diagnostic value. The agglutination test can appear in the first week of the disease course, and it is often strongly positive in the second to third weeks. Test tube method above 1:100 is meaningful. During the course of the disease, the titer increased by more than 4 times, which is of greater significance. However, inoculation of Brucella vaccine, cholera vaccine, typhoid vaccine, or brucellin intradermal test can increase the agglutination titer, so attention should be paid. In addition, the agglutination reaction may have a prozone phenomenon (negative at low dilution, and negative at high dilution), so the dilution should be at least 1:100. Some people believe that the presence of IgA antibodies causes the prozone phenomenon, while others believe that it is related to the ratio of IgA, IgG, and IgM. Prozone phenomenon can occur when IgA antibodies are the mainstay. The positive rate of agglutination in the acute phase is very high, up to 80% to 90%, while in the chronic phase it is low, only about 30%. An ELISA or anti-human globulin test should be performed when the agglutination test in chronic patients is negative. In order to distinguish between natural infection and artificial immunity, or to determine whether the disease is active, a 2-ME test can be used.
(2) Enzyme-linked immunosorbent test (ELISA):
1:320 is positive. The sensitivity is higher than that of the agglutination experiment, and the specificity is also very good. And can measure IgM, IgG, IgA antibodies separately. Among them, IgM antibodies appeared earlier, reaching a peak about 1 month after infection, and then began to decline. IgG antibodies are produced late, reaching a peak at 6 months, and then starting to decline after 10 months. The ebb and flow of IgA antibody is similar to that of IgG, and it is not easily destroyed by sulfhydryl compounds. The determination of different antibodies is helpful for the judgment of recurrence. IgG antibodies rise again when recurrence, but IgM and IgA antibodies often continue to decline. This method can also measure anti-cytoplasmic (CP) antibodies and anti-LSP antibodies respectively. The former has better specificity, but appears later, and early antibacterial treatment can affect its appearance. The latter appears earlier and is not affected by antibacterial drugs, but has a slightly lower specificity. Therefore, if both are tested at the same time, the effect is the best . This method can be used for the diagnosis of acute and chronic patients at the same time. Recently, avidin enzyme-linked immunosorbent assay has been used, which is more sensitive than ELISA.
(3) Complement fixation test:
1:16 is positive. Positive in the acute and chronic phases
The rate is higher than that of the agglutination test, and the specificity is also very strong, but the positive appears later, and the positive starts at the third week of the disease course, and the operation is more complicated, so it is only used for the difficult to diagnose, especially for chronic patients.
(4) Anti-human globulin test:
1:160 is positive. It is used to determine the incomplete antibody produced by the patient. Although the incomplete antibody can bind to the antigen, it is not visible to the naked eye. When the anti-human globulin immune serum is added to the antigen-incomplete antibody complex, a direct visible reaction occurs. Positives appear later and disappear slowly. It is more sensitive than the agglutination test and the complement fixation test, the positive rate is higher in the acute phase and the chronic phase, and the specificity is also stronger. However, the operation is more complicated, so it is only used for difficult cases, especially chronic patients.
(5) Other serological tests:
Passive hemagglutination test, agar diffusion test, indirect immunofluorescence test, immunoelectrophoresis and dot immunoassay (using silver-labeled cloth bacteria specific antigen) can be applied. However, the above method is not suitable for general use due to its complicated operation.
(6) 2-mercaptoethanol (2-ME) test
This method can detect IgG, which is used to distinguish natural infection and bacterial immunity. After 1 month of natural infection, the agglutination in the body is dominated by IgG type (initial IgM type), which is tolerant to 2-ME; and the lectins within 3 months after bacterial immunization are all IgM Master, can be destroyed by 2-ME.
(7) Intradermal test is delayed hypersensitivity
It starts to appear positive 2 to 3 weeks after the onset of the disease, and it can continue for several to 20 years after recovery. Therefore, when it is positive, it cannot be distinguished from the current patient or the previous infection. When it is negative, it does not support the diagnosis of the disease. Generally only used for epidemiological investigations.
4. Molecular biology examination
In recent years, some people have used primers that can amplify the 223bp gene fragment encoding Mr. 31*103 Brucella antigen for PCR to diagnose brucellosis. It is considered that the specificity and sensitivity are both good. Except for Ochrobactrum spp, other microorganisms related to Brucella in serology and phylogenesis were negative. Someone conducted this test on 31 patients with brucellosis and 45 healthy people. The result was 100% specific and the positive rate was 97%, and it was found that the positive rate of serum was higher than that of whole blood. Recently, some people have applied nest PCR, and it is believed that 30 bacteria can be detected without cross-reaction.
5. Other auxiliary examinations
X-ray examination can be used to check whether the bones and joints are diseased or not. It is also possible to check whether there are symptoms of heart and brain tissue infection through electrocardiogram and electroencephalogram.
Histopathology can produce epithelioid granulomas in the reticuloendothelial system such as lymph nodes, spleen, and liver. The histological changes of the skin lesions are often non-specific, there is a strong inflammatory reaction around the blood vessels, the vascular endothelium is obviously proliferated, and granulomas are formed.
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