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

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


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.

Funding Source

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

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.”

References :

  1. TB: New Blood Test for TB can Identify High-risk Individuals  – (https://doi.org/10.1093/cid/ciz548)

Source: Medindia