Method for surveillance of bovine brucellosis

Dear Sir,

Bovine brucellosis is an important infection that can be a public health threat. It is an important concern in tropical animal health and production. Prevention is a good concept and surveillance of this disease is a widely used technique for primary prevention.

Here, we would like to discuss the “method for surveillance of bovine brucellosis.” ^[1] At present, the molecular-based technique is a new alternative choice. There have been many discussions on this technique. Tiwari et al. recently noted that “RT-PCR targeting bcsp31 gene carried out on DNA extracted from serum or blood may not be a suitable method for surveillance of brucellosis in bovines.” ^[1] Surprisingly, Tiwari et al. reported that the molecular technique was inferior to classical tests [Rose Bengal plate test (RBPT) or standard tube agglutination test (STAT)]. ^[1] Indeed, the molecular diagnosis should have better diagnostic property. Many reports also showed good diagnostic property of the polymerase chain reaction (PCR) test. ^[2],[3] It is questionable whether there is any error or poor quality control in the PCR system by Tiwari et al. Indeed, there is no dispute that reverse transcription polymerase chain reaction (RT-PCR) is an excellent technique but that does not mean that this technology will prove to be equally good in all situations. PCR or RT-PCR detects DNA present in the samples. Brucella is an intracellular bacterium residing within the phagocytic cells like macrophages with the capability to multiply there. Bacteremia in cases of brucellosis is only transitory. Therefore, these bacteria are not found in blood all the time and thus, also in serum; they are present only intermittently. For this reason, the extraction of DNA from blood or serum is not always possible. Further, blood and serum contain many inhibitory substances affecting the sensitivity of RT-PCR. This could result in lower diagnostic sensitivity of PCR-based methods compared to serological tests when performed on clinical samples such as blood and serum. The samples reported by Tiwari et al. ^[1] were blood and serum on which RT-PCR was carried out. The results of RT-PCR were inferior to that of STAT and RBPT. This situation is very likely in the case of brucellosis because Brucella DNA may or may not be present in the serum of the infected bovine at the time of testing (i.e., collection of samples). On the other hand, the infected animal remains seropositive for long periods and detection of antibodies by RBPT or STAT is easy; hence, these tests could be better for the surveillance of brucellosis than RT-PCR as reported by Tiwari et al. ^[1] Nevertheless, the additional assessment of cost-effectiveness of the PCR test should be done, regardless of whether it has or does not have good diagnostic property. As far as cost-effectiveness of RT-PCR is concerned, RBPT for surveillance of brucellosis is highly cost-effective.

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1755-6783.162407