Scientists say they are close to developing a blood test that could identify millions of people who spread tuberculosis unknowingly. Researchers from the University of Southampton have discovered a group of biological markers that are found in high levels among infectious patients. Tuberculosis, or TB, is the world’s deadliest infectious disease and kills more than one million people each year, according to World Health Organisation data. The study, carried out with experts from the University of Cape Town in South Africa and Cayetano Heredia University in Lima, Peru, used a new technique that…