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New Blood Test can Predict Who are at High Risk for Tuberculosis

New Blood Test can Predict Who are at High Risk for Tuberculosis

Written by Dr. Kaushik Bharati, MSc, PhD, FRSPH (London)
Medically Reviewed by 
The Medindia Medical Review Team on July 10, 2019 at 6:42 PM
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  • A new blood test, called Actiphage, has been developed for the diagnosis of tuberculosis (TB)
  • The Actiphage test detects the causative bacterium, Mycobacterium tuberculosis, in the blood of TB patients
  • Also, the test is capable of identifying people who are at most risk of developing TB

A new blood test for diagnosing human tuberculosis (TB) is also capable of identifying those individuals at most risk of acquiring the disease. The new test, called Actiphage, detects Mycobacterium tuberculosis (MTB), the causative bacterium for TB, in the blood of TB patients.

The test has been developed by the National Institute for Health Research (NIHR) Leicester Biomedical Research Center (BRC) and the University of Nottingham's School of Biosciences, in collaboration with the Royal Veterinary College, UK. This novel test, which has been commercialized by PBD Biotech, UK, was originally meant for testing TB and Johne's disease in the blood and milk of livestock. This is the first time that it has been tested in humans. The research findings have been published in the journal Clinical Infectious Diseases.

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The study was led by Dr. Pranabashis Haldar, who is a Clinical Senior Lecturer in the Department of Respiratory Sciences, University of Leicester, UK.

The co-author of the paper was Dr. Catherine Rees, who is an Associate Professor of Microbiology at the School of Biosciences, University of Nottingham and Chief Scientific Officer at PBD Biotech, UK.

Facts about Tuberculosis (TB)

  • TB is the leading cause of death from an infectious disease
  • TB is present in a quarter of the world's population, mostly in the latent form
  • Latent TB has a 10 percent risk of progressing to the active form
  • Pulmonary TB is the most common type, affecting the lungs, although it can affect any part of the body
  • Pulmonary TB is transmitted through coughing and sneezing
  • Sputum examination is the most common test for diagnosis of pulmonary TB
  • Alternative tests for TB are lacking
  • In patients unable to generate sputum, diagnosis is delayed and there is a higher chance that the disease has already spread
  • England has one of the highest rates of TB in Western Europe
  • Rate of TB in the most deprived areas of the UK is over 7-times higher than in the least deprived

Technical Challenges in Developing the Actiphage Test

Mycobacterium tuberculosis (MTB), which is the bacterium that causes TB, is very different from common pathogenic bacteria. It grows extremely slowly, which makes it very difficult to grow in cell culture. Other advanced molecular biology techniques are also ineffective as the cell wall of MTB is so tough that it is difficult to extract the DNA (deoxyribonucleic acid) in order to carry out genetic analysis for diagnostic purposes.

The new Actiphage test, on the other hand, is very unique and novel. It uses a bacteriophage (a virus that specifically attacks bacteria) that infects live MTB, and multiplies inside the bacterium and breaks open the cell wall from the 'inside', as opposed to being broken by force exerted from the 'outside', which is used in conventional methods of DNA extraction. The Actiphage test can be completed within a matter of 6 hours, which is quite fast, considering the complexities involved.

Study Design

The study included 66 participants, divided into the following four groups:
  • Patients with active pulmonary TB
  • Patients with latent pulmonary TB
  • Patients with suspected pulmonary TB (1st Control Group)
  • Healthy individuals (2nd Control Group)

Study Findings

  • Actiphage was used to test all the participants twice, 12 months apart
  • 73 percent of patients tested positive with Actiphage - much higher than expected
  • All participants in the control groups tested negative with Actiphage
  • None of the latent TB cases who tested negative with Actiphage developed active TB
  • Two out of three latent TB cases who tested positive with Actiphage, subsequently developed active TB 6 months later
With reference to the study findings, Haldar says: "Our observations provide new insights into how human TB develops and support recent evidence of the existence of a transitional state of TB infection called incipient TB that does not produce symptoms but carries a high risk of progressing to active TB. There is potential for Actiphage to be developed, both as a mainstream blood test to diagnose TB and as a test used in screening programs to help us identify and treat people with latent infection."

He adds: "As a blood test, it is particularly suitable for patients unable to produce sputum, including children, and may help support diagnosis in underserved groups that struggle to access freely available healthcare resources."

Implications of the Study

The study implies that the Actiphage test has some degree of predictive power for identifying MTB-infected people who may subsequently develop full-blown TB.

Concluding Remarks

The research team is quite optimistic, based on the encouraging results, that the Actiphage test could be used as an effective tool for studying the dynamics of MTB infection in humans.

Rees concludes: "The new Actiphage blood test offers the potential to target those at risk of TB and allow treatment to start early. This is a very exciting development that invites further study."

Funding Source

The study was funded by the National Institute for Health Research (NIHR), UK.

Reference :
  1. A novel high sensitivity bacteriophage-based assay identifies low level M. tuberculosis bacteraemia in immunocompetent patients with active and incipient TB - (https://doi.org/10.1093/cid/ciz548)

Source: Medindia

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