Research and deliverables: The Indian scenario

Tuberculosis infection is a complex one. Pulmonary tuberculosis is categorized as latent, fresh, chronic, relapse and resistant and EPTB affecting other organs. Different hosts have shown variable immune response to the different antigens. Hospital-based evaluated studies by Harinath and others have shown TB ES-31 antigen in chronic PTB cases, ES-43 antigen in relapse cases, ES-41 antigen in bone and joint TB and elevated ES-20 antigen in weak immune response TB lymphadenitis patients. The antigen detection has been found to be a better marker than antibody in TB with HIV, further proving adjunct markers for increased sensitivity for TB detection.

A cocktail of antigens ES-31, ES-43 and ES-41 detecting antibody showed improved sensitivity (96 percent) in PTB cases. A cocktail of purified antibodies to ES-31, ES-43 andEST-6 (ES-41+ ES-38) showed a sensitivity of 91 percent for detection of antigen and 97 percent for immune complexed antigen with specificity of 95 percent and 99 percent respectively^3,4. In prospective study, the in-house developed SEVA TB ELISA analyzed for nine months in tuberculosis suspected patients showed 100 percent correlation (42 cases) with AFB positivity but were not ATT treated. This can make an important contribution in confirming TB and correlating with clinical decision in smear negative TB cases in PTB and EPTB as studied on hospital patients.

In one of the study explored by Kashyap and others reported ELISA for the detection of Ag 85 complex (30kDa protein) in CSF samples of TB meningitis with a sensitivity and specificity 89 percent and 92 percent . Mukherjee and others have explored the sero-diagnostic potential of a panel of RD1 antigens and culture filtrate proteins for diagnosis of PTB and EPTB. Among the antigens Rv 3872, Rv 3878, ESAT-6, CFP-10 and CFP-11, CFP-31, Ag85A and Ag 85B tested, Rv 3872 and its antigenic epitopes have emerged as promising antigens⁴.

Time to change thinking

However such tests are excluded from these systematic reviews in spite of decades of research performed to identify these target markers and assess their immunogenic and diagnostic potential. Although, the Government measures to ban certain serological tests is the well-come initiative due to lack of consistency in sensitivity and specificity but imposition of harsh policies through banning the serological immunodiagnostic kits are hampering promising molecules, which would otherwise aid in clinical decision making for diagnosis and proper management of TB patients.