In this presentation, I explain the diagnostic challenges in the diagnosis of Brucellosis.

1. Dr. Mohammad Hassan Jokar

2. Rose Bengal Plate Test (RBPT)
Wright test?
2ME test?
Prozone phenomenon?
Blocking Ab.?
Coombs Wright?

3. Why diagnosing brucellosis is challenging?
• People's reaction to brucella is highly variable
• The immunology of brucellosis is somewhat different.
• There are different subtypes of brucella
• Brucella is difficult to cultivate
• Abortus antigen is commonly used
• Serologic tests have false positive & negative

4. The trend of humoral response in
brucellosis

5. Diagnosis is based on :
•History of contact
•Clinical manifestations
•Laboratory changes

6. Common tests used for brucellosis diagnosis
•Rose Bengal Plate Test (RBPT)
•Standard tube agglutination (SAT) or wright test
•2ME wright
•Coombs Wright
•Brucella microagglutination test (BMAT)
•ELISA
•Bacterial culture
•Molecular methods; e.g. PCR

7. The role of serologic tests
•Serologic tests play a fundamental role in the diagnosis
•The interpretation of the results is usually difficult,
particularly in:
o Chronic brucellosis
o Reinfection, and relapse
o Endemic areas

8. Rose Bengal plate test
• Is an agglutination test in which the
brucella cells are bound to a dye
• Is quick and easy to read
• It is a useful screening test
• If + , standard tube agglutination test
should be used.

9. Standard tube agglutination test (wright)

10. SAT or Wright test
•Measures the total level of specific IgM and IgG.
•A fourfold or greater rise in titer to 1:160 (In IRAN ≥ 𝟏/𝟖𝟎) is
significant

11. SAT or Wright test
False positive results
•F. tularensis
•Y. enterocolitica
•V. cholera
•Salmonella
•Vaccine against F. Y. V & S.
•Stenotrophomonas maltophila

12. Wright test, False negative results
•First week of disease
•Disease due to Br. Canis
•Blocking Ab. (Chronic brucellosis)
•Prozone phenomenon

13. 2ME
• The addition of 2ME to the
SAT test results in the
destruction of disulfide bonds
of IgM
• 2ME test result is the detection
of only IgG

14. 2ME
• 2ME test will be negative if
SAT test is really negative
• 2ME test is less sensitive than
STA test
• The prognosis of acute
brucellosis may be predicted
from the fall of 2ME

17. SAT must be diluted to titers
1/2560 or more in order to
exclude false sero-negativity
in cases with clinical and
laboratory findings
suggesting brucellosis.

18. Blocking or incomplete Ab.
• Serum may contain brucella
antibodies which do not produce
agglutination
• Non agglutinating antibodies are
called incomplete antibodies
• Incomplete antibodies can be
detected by addition of rabbit
anti-human

20. Coombs Wright
• If SAT is negative and there are
symptoms and signs compatible with
chronic brucellosis, then coombs titer
of => 1:40 should be considered
positive
• Coombs test is not recommended
when STA test is positive