Two billion people worldwide carry the pathogen that causes
tuberculosis (TB), and most of them do not even know they are infected. This is
because some 90 percent of people with TB have "latent" infections.
They have no symptoms, they can't spread the disease to others and the bug
remains dormant in their lungs—often for years.
Detecting latent TB infections is an important public health
problem because those 10 percent of people who go on to develop full-blown
"active" TB will, in turn, infect another 10-15 people per year on
average. Such smoldering spread is one of the reasons why TB remains the
seventh-leading cause of death worldwide, killing more than 1.5 million people
every year.
Now a group of researchers at Colorado State University
(CSU) has demonstrated a sensitive new way to use light to detect traces of TB
bacteria in fluids. Their work, described by CSU graduate student Barbara Smith
at the Optical Society's (OSA) Annual Meeting, Frontiers in Optics (FiO), next week in San Jose,
Calif., may one day help health care workers identify people who are latently
infected. Moreover, the technology may be amenable for widespread use in the
developing world, where most cases of TB occur.
What is missing from the public health tool chest, says CSU
professor Diego Krapf, who led the research, is a technique that can be used to
widely detect TB in those places where it is most prevalent.
Krapf, Smith and their colleagues have developed a technique
that can sensitively detect different molecular markers indicating a TB
infection that would be cheap to use and no harder to administer than a common
pregnancy test, making it ideal for use in the developing world. The Colorado
researchers envision a device that would simply require someone to smear a drop
of blood or urine on a glass slide, insert it into a machine and read a simple
display that would indicate whether that person is infected or not.
Such a device could easily be built with existing
off-the-shelf technology, says Krapf, adding that it would be no more
complicated than the internal workings of a standard DVD player. The device
relies on specialized surface chemistry that avoids protein adsorption, except
for those molecules that need to be detected. Then, the presence of these
molecules is recorded by fluorescence using a red diode laser.
Once detected, TB infections are generally treatable with a
long course of antibiotics, and one of the basic strategies behind the World
Health Organization's current efforts to curb the spread of the disease
worldwide is to simply find the people who are infected and get them the
antibiotics they need.
The CSU development could one day play a role in curbing the
spread of TB. Currently, finding people who are infected is not so simple.
Doctors can spot suspected cases by taking chest X-rays, which may reveal
evidence of infection in the lungs. Or they can turn to a century-old technique
called a sputum smear, where a sample of coughed fluid is stained and examined
under a microscope for indications of the infection. Better yet, if doctors can
grow cultures of TB bacteria from lung fluid, they definitively know that a
person is infected.
These tests may not detect latent TB infections, however,
because people who are latently infected may not have enough bacteria in their
lungs to detect. For people with latent infections, other tests exist, but they
have their problems as well. A simple skin test exists, but it is only
sensitive enough to detect about half of all cases, says Krapf. Other more
sophisticated methods that rely upon detecting specific markers in the blood
are more sensitive, but they require special facilities and training that would
be far too expensive for widespread use in the developing world.
Krapf and his colleagues have been able to demonstrate the
feasibility of detecting markers of TB infections at great sensitivity in
saline solutions -- they were even able to detect a single molecular marker of
a TB infection in solution. They have not yet built a functioning device that
can detect hidden TB infections in blood or urine samples, and they have not
yet tested the technology on samples collected in the field. Before any such
detector is available for use in the field, it would have to be rigorously
tested in clinical trials.
Moving in that direction, the team plans to do a survey of
blood and urine samples from people infected with TB bacteria. This will help
them conclude how sensitive they need to make any detector and which markers
are the best to test.
FiO 2009 is OSA’s 93rd Annual Meeting and is being held
together with Laser Science XXV, the annual meeting of the American Physical
Society (APS) Division of Laser Science (DLS). The two meetings unite the OSA
and APS communities for five days of quality, cutting-edge presentations,
fascinating invited speakers and a variety of special events spanning a broad
range of topics in physics, biology and chemistry. The FiO 2009 conference will
also offer a number of Short Courses designed to increase participants’
knowledge of a specific subject while offering the experience of insightful
teachers. An exhibit floor featuring leading optics companies will further
enhance the meeting.
Meeting home page
Conference
program
Searchable
abstracts
Optical
Society of America