To commemorate World TB Day on Thursday 24 March, each day this week we will feature a different aspect of the fight against TB
Internationally, TB is one of the leading infectious causes of death, killing around two million people per year, particularly those who are poor. To conquer it, more than 70% of incident infectious TB cases must be detected annually and 85% of these must be successfully treated. World Health Organisation (WHO) data shows that the world is coming far short of detecting sufficient numbers of cases; the poorer countries have a particularly high burden of disease and particularly low case detection, consequently TB control is compromised.
In all countries the poor face the greatest burden of TB and are most likely to harbour the undetected cases. Patients face long care seeking pathways, characterised by multiple visits to healthcare providers and high costs associated with these pathways. Studies conducted by LSTM in urban Malawi found that the cost of accessing a diagnosis among the poor was around 50% of their annual income, despite tests being free at point of delivery.
New developments in diagnosis may reduce these costs substantially. WHO has approved a new case definition for TB, which allows a lower bacillary threshold for diagnosis; the use of a two, instead of three smear strategy; and frontloaded sample collection (allowing patients to provide two sputum samples on the same day and so reducing the number of patient visits. Another new tool, GeneXpert® MTB/RIF provides fast results and is able to detect more patients who would not be diagnosed through smear microscopy. Other tests to more quickly detect drug resistant strains have also become recently available. LSTM is at the forefront of efforts to ensure that all new tests and strategies are evaluated in ‘live’ health systems so that poorer countries may have access to optimal information on which to base their decisions around which diagnostic strategies to implement.
The NIHR funded Biomedical Research Centre in Microbial Diseases at Liverpool is a partnership between LSTM, RLUH and the University of Liverpool. The BRC has Respiratory Infection as a central theme and is committed to improvements in diagnosis and treatment of TB. The TB work of the BRC is carried out in LSTM’s Centre for Tropical Infectious Diseases, a state of the art laboratory dedicated to the study of infectious diseases. One of the TB projects focus on biomarkers for new diagnostics.
Our approach to new diagnostics has been to compare the proteins found in body fluids (blood, urine) in patients with TB and healthy comparison subjects. Several potentially discriminating proteins are now in advanced testing to determine if they might prove useful in the earlier or more accurate diagnosis of TB in patients in the UK and world-wide.
Application of TB Biomarkers for diagnostic potential
Although tuberculosis is curable and the rate of successful treatments is regarded as high, there remain large numbers of undiagnosed cases in many developing countries. It is estimated that only half of the TB cases in Africa are detected and recorded. Clearly, delays in diagnosis compound the rise in the global TB epidemic as undetected individuals remain untreated and increase disease transmission. Detection rates using sputum smear microscopy, the most common diagnostic test, can range from 20-80%. The sensitivity of this test is judged poor. The HIV/AIDS crisis creates an additional burden for care and treatment as TB resurges in immuno-compromised individuals. To date there is no simple, rapid, sensitive and specific test that can differentiate active TB from latent infection, and slowly progressive TB.
Our hypothesis is that the various states of tuberculosis result in production of characteristic protein signatures (biomarkers) which would be identified by mass spectrometry, and that specific diagnostic tests would discriminate, for example, latent from active TB infections. Biomarkers for TB that can be adapted to robust, point-of-care and affordable user-friendly formats that can replace sputum smear diagnosis and rapidly identify the various disease severities are urgently required.
Our progress to date
By employing proteomic strategies to study proteins from initial biological fluids from clinical cases of TB and control groups, as well as sourcing samples from sub-sets where HIV status has been confirmed, and subjecting initial results to more detailed bioinformatic analysis, we have discovered panels of novel discriminating proteins and have shown that their presence is more prominent in one disease process compared with another. In addition, small-scale orthologous experiments have been carried out which have demonstrated the potential of immune-reactive detection for selected biomarkers, thus validating our approach.
In future work, we will:
- Confirm the validity of discriminatory biomarkers within differing biological samples using specific antibodies in robust immune-reactive techniques.
- Test the suitability and credibility of selected biomarkers for diagnostic development on a wider batch of archived clinical samples.
- Develop prototype immune-diagnostic tests in collaboration with commercial partner(s).