Method | Strengths | Limitations | Recommendations |
Indirect methods Serology | |||
Rose Bengal Plate Test (RBPT) | · Highly sensitive, inexpensive, simple, and rapid to perform. · Detects mainly IgM and requires essential laboratory equipment and expertise. | · Low specificity, false-negative and false-positive results and not recommended for diagnosing chronic brucellosis. | · Applicable as a rapid diagnostic test. · Confirmation of results is required, using either CFT or ELISA. |
Indirect Enzyme-linked immunosorbent assay (iELISA) | · High sensitivity, is affordable, has shorter run times and requires less interpretation training. · More sensitive than RBT. More sensitive and specific than SAT · Measures various antibody titers (IgG, IgM, and IgA). | · Low specificity, lower than RBT. | · Appropriate in diagnosing various stages of infection, chronic brucellosis cases, and detecting incomplete antibodies. · Ideal for screening purposes. |
Competitive Enzyme-linked immunosorbent assay (cELISA) | · High specificity. | · Lower sensitivity than iELISA and species unspecific. | · Applicable for various animal species. Can process poor quality samples such as hemolysed blood and use for the confirmation of brucellosis. |
Complement fixation test (CFT)
| · Very specific, detecting IgM and IgG1 antibodies. · Detects incomplete antibodies, as well as the slightest changes in antibody titres. | · False-negative results were recorded when IgG2 antibodies impede complement fixation. · Not appropriate in detecting recent infections in cattle. · Requires expertise for interpretation. · The quality of its results is affected by the sample quality and the standardisation of the antigen. | · It is fitting for control and surveillance programs. · It is used together with RBT as a confirmatory test. |
Slow Agglutination Test (SAT) | · Designed mainly to detect IgM. | · Low sensitivity and specificity, slow and not advisable for use in individual animals. · Not applicable for the detection of chronic brucellosis | · Suitable in detecting brucellosis on a herd basis. · Use in routine diagnosis, complemented with Brucella Coombs test. |
Slow agglutination of Wright with EDTA (SAW-EDTA) | · Sensitive, designed for the detection of IgM. | · Laborious and time-consuming. | · It has been replaced by slide, plate and card agglutination tests. |
Lateral flow assay (LFA)
| · Sensitive and specific, as sensitive as the RBT but having a much higher specificity. · Can distinguish between IgM and IgG antibodies. · More accurate and specific than the SAT in chronic and complex cases. | · Not suitable for large-scale screening. | · Appropriate for rapid field or bedside testing in endemic areas and where laboratories lack modern facilities. · Suitable in the confirmation of RBT results. · It can be used by smallholder herds to screen for and remove infected cattle or to reject milk from infected cattle. |
Direct detection | |||
Cellular test Delayed hypersensitivity test for brucellin (DHTB) | · High specificity in non-vaccinated cattle. It detects antigens before the circulating antibodies appear and are more specific than RBT and CFT. | · Lower specificity in vaccinated cattle. Low sensitivity and may sensitise cattle that have not been exposed to the infection. | · Results should be combined with serology for confirmation at herd levels before the slaughter of infected cattle. |
Culture | · The gold standard provides the definitive diagnosis of the disease with good specificity. | · It requires biosafety level 3 precautions, takes a minimum of 4 - 5 days to grow in culture and is costly. · Sensitivity is problematic in cases where the fever is intermittent. · In chronic disease, culture results may be negative due to bacterial eradication without complete clinical recovery. | · Application is not feasible in the routine diagnosis of the disease. · Useful in research for identifying the species in circulation. |
Polymerase chain reaction (PCR)
| · Provides rapid detection and confirmation of Brucella with high specificity and low cost. · It is more sensitive and safer than blood culture and more specific than serologic methods in diagnosing acute disease. · The PCR-ELISA molecular method is more sensitive than other methods, with a semi-quantitative ability. | · Sensitivity and accuracy are dependent on the DNA extraction method and the quality of extracted genomic DNA. · Challenges are faced in standardising extraction methods; infrastructure, equipment and expertise are still lacking. · It has a lower sensitivity than ELISA, and sensitivity can also be reduced in chronic brucellosis. · Its complexity contributes to the limited application in routine laboratory practice. | · It is applicable in assessing the treatment efficacy, species differentiation and biotyping of isolates and is convenient for diagnosing human brucellosis. · The combined use of PCR and ELISA diagnostic tests can improve and overcome limitations in diagnosing brucellosis. |
Sequencing | · It gives an insight into the genetic bases for host preference, pathogenesis, virulence, biotype differences and phylogenetic relationships. · Enables the identification of potential targets for the development of vaccines and diagnostics to prevent and control brucellosis. | · Equipment is expensive, not readily available, and requires trained staff to carry out the procedures. | · Applicable for research on genetic variability, geographical distribution and host preferences. |