Quicker detection of TB and hepatitis

THE long anxious wait for a sputum or blood test report to confirm whether that persistent cough is tuberculosis, or the unexplained, but constant fatigue and failing appetite is hepatitis B could soon be shortened from days to just a few hours.

Results of recent clinical trials of techniques developed by scientists at the Delhi-based National Institute of Immunology (NII) reveal that the tests besides taking lesser time are also more accurate than the current ones. Says Pramod Khandekar, a member of the NII research team, "The clinical trials carried out in hospitals at Delhi and Lucknow were very successful. These kits can detect 19 out of a possible 20 cases, a success rate much higher than conventional tests." The success rate for conventional tests is about 80 per cent. A report of the clinical trials, he adds, has already been submitted to a joint committee of the department of biotechnology and the Indian Council for Medical Research, to decide whether this technology should be transferred to the diagnostics industry.

Both tuberculosis and hepatitis B are major health problems in India. About 10 million people suffer from tuberculosis and the disease claims as many as 500,000 lives each year. Hepatitis B is even more widespread with its carriers numbering over 40 million. "Diagnosis of these diseases by conventional methods," says Khandekar, "is not only time consuming, but often tests also fail to detect the presence of the causative agents."

Usually, a sensitive and accurate diagnosis of tuberculosis takes 6-8 weeks. But this test still cannot detect bone and skin tuberculosis. Hepatitis B tests currently used are based on the body's immune response to the hepatitis B virus and often fail to detect the disease.

The techniques developed at NII are based on an analysis of the molecular structure of the genetic material, or DNA, of the disease-causing bacteria or virus. The DNA molecule is a double-stranded structure which can be unzipped and rezipped much the same way as a garment zipper. Moreover, there is only one particular way the molecule can be rezipped. Using this property, the scientists have developed DNA probes -- radioactively-labelled single-stranded fragments of the bacterial or viral DNA -- that can recognise and join up with the DNA of the pathogen. The DNA probes carry genetic sequences peculiar to the disease-causing pathogens and so ensure their fool-proof detection.

If, as in the early stages of infection, the number of disease-causing organisms is small, Khandekar's team has refined a technique known as the polymerase chain reaction, which was developed in the US in the '80s. This amplifies the amount of pathogenic DNA, making it easier to use DNA probes. Khandekar says, "The PCR technique is capable of detecting as few as 9-10 bacilli in the case of tuberculosis, and can detect as few as 3 hepatitis B viral particles."