Imperial College London (10.22.2013)
This article by Imperial College London discusses a study in which researchers were able to discern active TB from latent TB infection and other diseases by the genes that are switched on in individuals with suspected TB disease. The symptoms of active TB, which include coughing and weight loss, can be found in other diseases, while latent TB infection has no symptoms.
In the developed world, healthcare providers use immunological tests to investigate the immune system’s responses to TB bacteria, but these tests do not distinguish between active and latent TB infection. In Africa, where rates of TB are high, tests are not very reliable. Healthcare providers usually diagnose TB using the sputum test but patients with HIV/TB coinfection may have low levels of bacteria in their lungs, resulting in a negative test. The other test used is the culture test, which takes approximately six weeks and is not available at many hospitals. Doctors usually depend on clinical features and chest X-rays, but are unable to tell whether the patient has TB or a chest infection such as pneumonia.
In this study, international researchers, led by Professor Michael Levin of Imperial College London, used molecular techniques to determine which genes are switched on in TB patients and whether the genes could be a reliable indicator of the disease. The researchers used 584 patients with suspected TB from two clinics in South Africa and Malawi throughout four years and used various tests to make an accurate diagnosis. The researchers analyzed patients’ blood samples and found they could distinguish active TB from latent TB and other diseases by determining which genes are switched on in people with suspected disease. When the genes are switched on, the genetic code is copied onto molecules of RNA, which can be detected in the blood. The researchers hope to use this data to develop a simple, affordable test that can be used in Africa and other resource-poor areas.
An EU Action for Diseases of Poverty program grant funded this study.
The full report, “Detection of Tuberculosis in HIV-Infected and -Uninfected African Adults Using Whole Blood RNA Expression Signatures: A Case-Control Study,” was published online in the journal PLOS Medicine (2013; doi:10.1371/journal.pmed.1001538).