Beetle-powered TB test aids diagnosis in HIV patients

Researchers at Tulane University developed the device, known as ASTRA (antigen-specific T-cell response assay). It uses a chemical reaction inspired by the defence mechanism of bombardier beetles to operate without electricity.

Senior author Tony Hu is Weatherhead presidential chair in biotechnology innovation at Tulane University and director of the Tulane Centre for Cellular & Molecular Diagnostics.

Hu said: “The goal was to develop a TB test that could be taken anywhere and provide quicker, more accurate results for anybody,.

“Current tests such as the IGRA are cost-prohibitive or require access to facilities that resource-limited communities don’t have.

“If we are going to eliminate TB, we have to diagnose and treat as many infection cases as possible.”

ASTRA requires only a drop of blood and provides same-day results in around four hours. By contrast, interferon-gamma release assay (IGRA) blood tests take 24 hours and skin tests typically take two to three days.

When tested against IGRA, ASTRA detected TB in HIV-positive individuals with 87 per cent specificity, compared to 60 per cent for IGRA. It also showed improved detection in TB cases not involving HIV.

Tuberculosis affects an estimated 2 billion people globally, with more than 90 per cent carrying latent TB – a symptom-free, non-infectious form.

In people with HIV, a weakened immune system increases the likelihood of latent TB becoming active and potentially deadly.

TB remains the leading cause of death among people with HIV worldwide.

To overcome the limitations of immune-based diagnostics in HIV-positive patients, the team identified two new biomarkers – biological indicators of TB infection – that do not rely on immune cells compromised by the virus.

To conduct the test, a drop of blood is added to the device and incubated for four hours.

A preloaded reagent acts as a kind of molecular “wanted poster”, prompting immune cells to respond if they have previously encountered TB bacteria.

To power the test without electricity, the researchers used a mechanism inspired by bombardier beetles, which defend themselves by mixing two chemicals to create a spray.

ASTRA replicates this by combining two chemicals that propel the blood sample across a chip for analysis.

Bo Ning is lead author and assistant professor of biochemistry at Tulane University School of Medicine.

The researcher said: “If your community has an immunocompromised population, someone may have latent TB.

“This can help block the spread of TB and ensure that no one slips through the cracks.”

The device was validated using samples from Eswatini, a country with high TB rates and the highest recorded HIV prevalence globally, at 27.3 per cent.

Hu said: “The sooner you have a diagnosis, the sooner you can begin the process of determining proper treatment.

“TB is the No. 1 pathogen HIV patients worry about globally. If treatment is available, we should be working to kill these bacteria, latent or not.”