Non-medical personnel can operate
the devices and diagnose in seconds
Researchers in the U.S. have come
up with a way to rapidly diagnose malaria simply by shining brief pulses of
light from a laser through the skin.
“This method is distinct from all
previous diagnostic approaches, which all rely upon using a needle to obtain
blood, require reagents to detect the infection, and are time- and
labour-consuming,” noted the scientists in a paper published this week in the
Proceedings of the National Academy of Sciences (PNAS).
Rugged and inexpensive
microlasers exist that could be modified to create portable devices capable of
operating in harsh conditions. Non-medical personnel would be able to operate
these devices and obtain a diagnosis in seconds, according to their paper.Such a device was under
development, said Rice University’s Dimtri O. Lapotko, the senior author of the
paper, in an email.When a malaria parasite invades
red blood cells, it gorges on the haemoglobin those cells contain. Haemoglobin
is the molecule that helps carry oxygen to all parts of the body. The parasite
turns the iron-containing haeme component, which can be toxic for the organism,
into an insoluble pigment, haemozoin.
The technique developed by Dr.
Lapotko and his colleagues relies on detecting the haemozoin in red blood
cells. They achieve this by using a narrow band of near-infrared light that is
strongly absorbed by haemozoin but not haemoglobin.A brief pulse of light in this
band from a low-power laser heated up the tiny particles of haemozoin, causing
a “vapour nanobubble” to form in the fluid around each particle. These bubbles
expand explosively and then collapse with a characteristic sound that could be
picked up with an ultrasound sensor.The scientists demonstrated the
technique in animal trials using malaria-infected mice.A probe that carried an optical
fibre as well as an ultrasound sensor was clamped to the ear of the mice so
that laser light could be shone at a surface blood vessel and the resulting
sounds recorded.The device was able to accurately
pick out infected animals, even when only about one in a million red blood
cells carried the parasite, their paper reported.The first trials of the
technology in humans was expected to begin in early 2014 at Houston where Rice
University is based, according to a University press release quoting Dr.
Lapotko.
“It is a fantastic technique” but
has an important limitation, observed Vinod Prakash Sharma, who was founder
director of the National Institute of Malaria Research in New Delhi.The method would be unable to
distinguish between two species of the parasite, Plasmodium falciparum and
Plasmodium vivax, that cause malaria in India. Treatment depended on which
parasite was infecting a patient.The technique described in the
PNAS paper would therefore have to be combined with ways of discriminating
between the two, Dr. Sharma told this correspondent.Moreover, haemozoin may persist
in the blood even after the parasite has been cleared, remarked V. Arun
Nagaraj, Ramanunjan Fellow at the Indian Institute of Science in Bangalore.
With this technique, a previously-infected individual who had another bout of
fever from some other cause might potentially be misdiagnosed as having
malaria.
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