TB or Not TB?: Novel Detector Could Shorten Testing Times, Aid Treatment Efforts

Colorado State University researchers have developed a device for use in the field that can identify both active tuberculosis infection and dormant microbes, which could flare up into full-blown illness*

By Adam Marcus
Scientific American Online

University of Colorado researchers have developed a device for use in
the field that can identify both active tuberculosis infection and
dormant microbes that could flare up into full-blown illness

Tuberculosis is a serious public health challenge in the developing
world, where the infection claims roughly two million lives each year,
according to the World Health Organization (WHO). Yet the disease, which is a leading killer of patients with HIV/AIDS, is cumbersome to detect, resulting in delayed or inappropriate treatment, greater spread of the infection and preventable deaths.

So, researchers in Colorado are developing a portable, rapid TB sensor
that could help reduce the death toll and make treatment more efficient.

This "field friendly" device relies on readily available and relatively
low-cost components and can find the lethal pathogen in blood in just 20
minutes, says Diego Krapf, an applied physicist and assistant professor
of engineering at Colorado State University in Fort Collins, who
designed the new device. That is far faster than conventional methods
such as sputum tests, which examine secretions from the lungs and
bronchi and can take days-sometimes weeks-to return results. The new
detector can identify active infection as well as dormant, or latent,
microbes that might one day flare up into full-blown illness, the
developers say. It also can distinguish between patients who carry TB
and those who once were infected but have successfully fought off the
illness.

"Our detector senses proteins, not an immune response against them,"
Krapf says. "The benefit of doing this is that while proteins mark the
presence of disease, antibodies remain in the organism after the disease
is long gone." So the new approach greatly reduces the chances of false
positives.

Krapf and his colleagues built a shoe box-size prototype with
off-the-shelf parts including diode lasers from CD and DVD players,
photodiode detectors, and other low-cost electronics. A handheld version
could easily be made from somewhat more expensive components, he says.

The detector works by a capture-illuminate process: It first analyzes a
blood sample in search of two TB proteins-antigen 85b and
alpha-crystallin. If either is present, it will bind to a specific molecular brush linked to immune molecules, called antibodies, which
affix to antigen 85b and alpha-crystallin but reject all other proteins.
Then a bath of additional TB-sensitive antibodies, modified with a gene
that produces fluorescence, is added. The result is in effect a glowing
antibody-TB-antibody protein sandwich.

Kathy Orloski, a veterinary epidemiologist at the U.S. Department of
Agriculture's National Tuberculosis Eradication Program in Fort Collins,
Colo., says the country's cattle industry would welcome a rapid test for
bovine TB. Cows currently are screened for the disease with skin tests
like those used in people, a process that requires animals to be handled
twice in three days, driving up costs for ranchers. Dairy or beef cattle
infected with TB are euthanized, she says.

Government inspectors at slaughterhouses would likewise benefit from an immediate on-site detection method, helping them identify carcasses of
infected cows faster than current laboratory testing, which takes up to
48 hours to process tissue samples. "A test used in this capacity would
have to be very accurate," Orloski says, "because the United States
slaughters 33 million cattle each year."

The government also would like to see a speedier way of testing the
million-odd cows imported each year from Mexico, which has had a problem with bovine TB in its beef and dairy stock for several years, Orloski says. Whereas Mexico and Canada are the two leading exporters of cattle to the U.S., Canadian cattle have for the most part been TB-free for the past decade, with the exception of certain areas of Manitoba.

http://www.scientificamerican.com/article.cfm?id=tuberculosis-detector